Journal of Colloid And Interface Science (v.316, #2)
Rapid evaporation-induced synthesis of monodisperse budded silica spheres
by Hongmin Chen; Junhui He (pp. 211-215).
Budded silica spheres have been synthesized by a novel rapid evaporation-induced self-assembly combined with the well-known Stöber method. The morphology of budded silica spheres were examined by transmission electron microscopy, and their mean size and size distribution were also estimated. Both the temperature of the sol–gel reaction and following post-treatment were found to play crucial roles in determining the surface morphology of obtained silica spheres and the yield of budded silica spheres. The possible formation mechanism was also proposed on the basis of experimental observations. The budded silica spheres would have higher surface areas than smooth silica spheres, and significant potentials for catalyst supports, building blocks of photonic crystals, and for constructing superhydrophobic and superhydrophilic surfaces.Budded silica spheres were facilely synthesized by a novel rapid evaporation-induced approach. The temperature of the sol–gel process and post-treatment of reaction mixtures were found to play crucial roles in determining the morphologies of silica spheres.
Keywords: Self-assembly; Budded silica spheres; Evaporation-induced synthesis; Hierarchical structures; Stöber method
Calcined Mg–Fe–CO3 LDH as an adsorbent for the removal of selenite
by J. Das; B. Sairam Patra; N. Baliarsingh; K.M. Parida (pp. 216-223).
Mg–Fe–CO3 layered double hydroxide (LDH) with a Mg/Fe molar ratio of 2.0 was synthesized by co-precipitation method and its calcined product (CLDH) was obtained by heating Mg/Fe-LDH at 500 °C. Sorption of SeO2−3 on CLDHs was studied and the results indicate that the sorption capacity of CLDHs was higher than that of uncalcined LDHs. Isotherms for SeO2−3 sorption by CLDHs were well described using the Freundlich and Langmuir equations. The thermodynamic parameters, viz.ΔG∗,ΔH∗,ΔS∗ were calculated to predict the nature of adsorption. The negative and positive values ofΔG∗ andΔH∗ indicate that the adsorption process is spontaneous and endothermic in nature, respectively. The adsorption process followed first-order kinetics.The adsorption of selenite on calcined Mg/Fe LDH is appreciably higher (64.0%) than the same through anion exchange of uncalcined precursor (52%). The decrease in the exchange ability of uncalcined LDH may be caused due to the strong interaction of CO2−3 in the interlayer space with the metal hydroxide layer.
Keywords: Calcined Mg–Fe–CO; 3; Layered double hydroxide; Adsorption; Selenite; Thermodynamic parameters
Removal of lead from aqueous solutions using Cassia grandis seed gum-graft-poly(methylmethacrylate)
by Vandana Singh; Stuti Tiwari; Ajit Kumar Sharma; Rashmi Sanghi (pp. 224-232).
Using persulfate/ascorbic acid redox system, a series of Cassia grandis seed gum-graft-poly(methylmethacrylate) samples were synthesized. The copolymer samples were evaluated for lead(II) removal from the aqueous solutions where the sorption capacities were found proportional to the grafting extent. The conditions for the sorption were optimized using copolymer sample of highest percent grafting. The sorption was found pH and concentration dependent, pH 2.0 being the optimum value. Adsorption of lead by the grafted seed gum followed a pseudo-second-order kinetics with a rate constant of4.64×10−5g/mg/min. The equilibrium data followed the Langmuir isotherm model with maximum sorption capacity of 126.58 mg/g. The influence of electrolytes NaCl, Na2SO4 on lead uptake was also studied. Desorption with 2 N HCl could elute 76% of the lead ions from the lead-loaded copolymer. The regeneration experiments revealed that the copolymer could be successfully reused for at least four cycles though there was a successive loss in lead sorption capacity with every cycle. The adsorbent was also evaluated for Pb(II) removal from battery waste-water containing 2166 mg/L Pb(II). From 1000 times diluted waste water, 86.1% Pb(II) could be removed using 0.05 g/20 ml adsorbent dose, while 0.5 g/20 ml adsorbent dose was capable of removing 60.29% Pb from 10 times diluted waste water. Optimum Pb(II) binding under highly acidic conditions indicated that there was a significant contribution of nonelectrostatic interactions in the adsorption process. A possible mechanism for the adsorption has been discussed. Cassia grandis seed gum-graft-poly(methylmethacrylate) was synthesized and evaluated for lead(II) removal from the aqueous solutions. The adsorbent was found useful in treating waste water contaminated with low concentration of Pb(II).
Keywords: Cassia grandis; seed gum; Grafting; Methylmethacrylate; Lead adsorbent
Effects of nanorod structure and conformation of fatty acid self-assembled layers on superhydrophobicity of zinc oxide surface
by Chantal Badre; P. Dubot; Daniel Lincot; Thierry Pauporte; Mireille Turmine (pp. 233-237).
Superhydrophobic surfaces have been prepared from nanostructured zinc oxide layers by a treatment with fatty acid molecules. The layers are electrochemically deposited from an oxygenated aqueous zinc chloride solution. The effects of the layer's structure, from a dense film to that of a nanorod array, as well as that of the properties of the fatty acid molecules based on C18 chains are described. A contact angle (CA) as high as 167° is obtained with the nanorod structure and the linear saturated molecule (stearic acid). Lower values are found with molecules having an unsaturated bond on C9, in particular with a cis conformation (140°). These results, supplemented by infrared spectroscopy, indicate an enhancement of the sensitivity to the properties of the fatty acid molecules (conformation, flexibility, saturated or not) when moving from the flat surface to the nanostructured surface. This is attributed to a specific influence of the structure of the tops of the rods and lateral wall properties on the adsorption and organization of the molecules. CA measurements show a very good stability of the surface in time if stored in an environment protected from UV radiations.Effect of nanorod structure and conformation of fatty acids on ZnO superhydrophobicity.
Keywords: Biomimetic; Superhydrophobic zinc oxide; Electrodeposition; Surface derivatization; Fatty acids orientation; Well-packed monolayers
Interaction of N-nitrosodiethylamine/bovine serum albumin complexes with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine monolayers at the air–water interface
by D.E. Valencia-Rivera; A. Básaca-Loya; M.G. Burboa; L.E. Gutiérrez-Millán; R.D. Cadena-Nava; J. Ruiz-García; M.A. Valdez (pp. 238-249).
We report the effect of N-nitrosodiethylamine (NDA) on the interaction between bovine serum albumin (BSA) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine monolayers (DPPC) at the air–water interface. We prepared aqueous solutions of NDA/BSA complexes maintaining a constant concentration of BSA of1.49×10−9M and using NDA concentrations to obtain 2000, 4000, 6000, 12,500, and 25,000 NDA/BSA molar ratios. The hysteresis area and the compressional modulus of the compression–expansion cycles performed at different times were dependent on the NDA concentration. The cycles performed demonstrate the stability of the new phase of DPPC/BSA and DPPC/NDA/BSA monolayers. This was achieved probably because the BSA concentration used was lower than the one needed for BSA to inhibit the return of DPPC molecules to the interface. Results of the compressional modulus at the onset of the new phase, obtained around 17 mN/m, 15 min and 1, 3, 5, and 12 h after DPPC deposition, indicated that the3.0×10−6M NDA concentration produced a more rigid film, probably due to the higher α-helix content of BSA. AFM images were obtained for DPPC/BSA and two DPPC/NDA/BSA complexes. Our images show that 12,500 NDA/BSA molecules were mostly adsorbed in the liquid condensed phase. However, BSA molecules were distributed more homogeneously.Behavior of the interaction of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) with bovine serum albumin (BSA) and different N-nitrosodiethylamine/BSA complexes at the air–water interface are investigated. A stronger interaction of DPPC/BSA and DPPC/NDA/BSA was found.
Keywords: DPPC monolayers; BSA; N; -nitrosodiethylamine; AFM; Compressional modulus
Nanoparticles of octakis[3-(3-amino-1,2,4-triazole)propyl]octasilsesquioxane as ligands for Cu(II), Ni(II), Cd(II), Zn(II), and Fe(III) in aqueous solution
by Newton Luiz Dias Filho; Reginaldo Mendonça Costa; Fabiane Marangoni; Denise Souza Pereira (pp. 250-259).
Nanoparticles of octakis[3-(3-amino-1,2,4-triazole)propyl]octasilsesquioxane (ATZ-SSQ) were tested as ligands for transition-metal ions in aqueous solution with a special attention to sorption isotherms, ligand–metal interaction, and determination of metal ions in natural waters. The adsorption potential of the material ATZ-SSQ was compared with related [3(3-amino-1,2,4-triazole)propyl]silica gel (ATZ-SG). The adsorption was performed using a batchwise process and both organofunctionalized surfaces showed the ability to adsorb the metal ions from aqueous solution. The Langmuir model was used to simulate the sorption isotherms. The results suggest that the sorption of these metals on ATZ-SSQ and ATZ-SG occurs mainly by surface complexation. The equilibrium condition is reached at time lower than 3 min for ATZ-SSQ, while for ATZ-SG is only reached at time of 25 min. The maximum metal ion uptake values for ATZ-SSQ were higher than the corresponding values achieved with the ATZ-SG. In order to obtain more information on the ligand–metal interaction of the complexes on the surface of the ATZ-SSQ nanomaterial, ESR study with various degrees of copper loadings was carried out. The ATZ-SSQ was tested for the determination (in flow using a column technique) of the metal ions present in natural waters.Isotherms of adsorption of transition-metal ions by a nanoadsorbent based on silsesquioxanes.
Keywords: Silsesquioxane; Silica gel; Adsorption; Isotherms of adsorption; Transition-metal ions
Influence of anions on the adsorption kinetics of salicylate onto α-alumina in aqueous medium
by Jayanta M. Borah; Manash R. Das; Sekh Mahiuddin (pp. 260-267).
The adsorption kinetics of salicylate on α-alumina surfaces were studied at 25 °C and pH 6 in the presence of 0.05 mM concentration of different anions (Cl−, Br−, I−, SCN−, HCOO−, CH3COO−, S2O2−3, CO2−3, and SO2−4) as a function of time. The experimental data were significantly better fitted to a pseudo-second-order kinetics equation of nonlinear form in the entire time duration and are in excellent agreement with corresponding estimated values. Considering adsorption data for salicylate in the presence of Cl− as the face value, all the monovalent anions (Br−, I−, SCN−, HCOO−, CH3COO−) promote the adsorption of salicylate onto α-alumina surfaces while the divalent anions (S2O2−3, CO2−3, and SO2−4) have the reverse effect under similar conditions. DRIFT spectra of α-alumina treated with salicylate reveal that the symmetric peak νs(COO−) is shifted by ∼40 cm−1 to a lower wavelength region, which implies that salicylate forms an inner-sphere complex with α-alumina surface in the presence of both mono- and divalent anions.The nonlinear pseudo-second-order kinetics equation was better than the linear form. Monovalent anions promote the adsorption of salicylate onto α-alumina surfaces while the divalent anions have the reverse effect.
Keywords: Adsorption; Kinetics; Salicylate; Alumina; Anion effect; DRIFT
Chromium(III) removal from water and wastewater using a carboxylate-functionalized cation exchanger prepared from a lignocellulosic residue
by T.S. Anirudhan; P.G. Radhakrishnan (pp. 268-276).
This study concerns with the development of a new cation exchanger (SDGPMASPCOOH) carrying spacer (SP) group [CONH(CH2)2NHCO(CH2)2] and carboxylate functional group at the chain end. The preparation process was carried out through graft copolymerization of methacrylic acid onto sawdust, SD (a lignocellulosic residue) using ceric ammonium nitrate as an initiator. The poly(methacrylic acid) grafted SD (SDGPMA) was subsequently treated with thionyl chloride followed by ethylenediamine (transmidation) and succinic anhydride (carboxyfunctionalization) treatments. Infrared spectroscopy and potentiometric titrations were used to confirm graft copolymer formation and carboxylate functionalization. The effectiveness of the SDGPMASPCOOH in removing Cr(III) from water and wastewater was evaluated by the batch technique. The influence of different experimental parameters such as solution pH, contact time, absorbent dose, Cr(III) concentration and temperature on removal process was evaluated. The maximum Cr(III) removal was observed at the initial pH of 7.0. The Cr(III) was removed by SDGPMASPCOOH up to 99.3 and 92.6% from an initial concentration of 10 and 25 mg/L, respectively, at pH 7.0. Equilibrium time was reached within 4 h. Kinetic data were analyzed using the pseudo-first-order, pseudo-second-order and Elovich equations. The data fitted very well to the pseudo-second-order rate expression. The Langmuir, Freundlich and Temkin equations were applied to the experimental isotherm data and the Langmuir model was found to be in better correlation with the experimental data. The monolayer adsorption capacity for Cr(III) removal was found to be 36.63 mg/g. The adsorption efficiency towards Cr(III) removal was tested using simulated tannery wastewater. The adsorbed Cr(III) on SDGPMASPCOOH can be recovered by treating with 0.1 M HCl. Four adsorption/desorption cycles were performed without significant decrease in removal capacity. The results showed that SDGPMASPCOOH developed in this study exhibited considerable adsorption potential for application in removal of Cr(III) from water and wastewaters.A new cation exchanger (SDGPMASPCOOH) prepared from sawdust (SD) has been used for the removal and recovery of chromium(III) from water and wastewater.
Keywords: Cr(III) adsorption; Sawdust; Kinetics; Isotherm; Desorption
Mechanism study on adsorption of acidified multiwalled carbon nanotubes to Pb(II)
by Hongjuan Wang; Ailin Zhou; Feng Peng; Hao Yu; Jian Yang (pp. 277-283).
Adsorption of acidified multiwalled carbon nanotubes (MWCNTs) to heavy metal using Pb(II) as a model was investigated and characterized by many techniques. The main adsorption mechanism of acidified MWCNTs to Pb(II) is proposed on the basis of adequate analysis. The results show that the oxygenous functional groups can be formed on MWCNTs after MWCNTs were treated by concentrated nitric acid. The oxygenous functional groups play an important role in Pb(II) adsorption to form chemical complex adsorption, which accounts for 75.3% of all the Pb(II) adsorption capacity. The Pb(II) in the form of PbO, Pb(OH)2, and PbCO3 adsorbed on the surface of the acidified MWCNTs is only 3.4% of the total Pb(II) adsorption capacity. The Pb(II) species adsorbed on acidified MWCNTs mainly aggregate on the ends and at the defects sites on the acidified MWCNTs.The oxygenous functional groups on the surface of acidified multiwalled carbon nanotubes play important role for Pb(II) adsorption, which accounts for 75.3% of all the Pb(II) adsorption capacity.
Keywords: Adsorption; Acidified MWCNTs; Surface functional groups; Adsorption capacity; Adsorption mechanism
Treatment of methyl orange by calcined layered double hydroxides in aqueous solution: Adsorption property and kinetic studies
by Zhe-Ming Ni; Sheng-Jie Xia; Li-Geng Wang; Fang-Fang Xing; Guo-Xiang Pan (pp. 284-291).
Adsorption of a weak acid dye, methyl orange (MO) by calcined layered double hydroxides (LDO) with Zn/Al molar ratio of 3:1 was investigated. In the light of so called “memory effect,” LDO was found to recover their original layered structure in the presence of appropriate anions, after adsorption part of MO− and CO2−3 (come from air) intercalated into the interlayer of LDH which had been supported by XRD and ICP. The results of adsorption experiments indicate that the maximum capacity of MO at equilibrium (Qe) and percentage of adsorption ( η%) with a fixed adsorbent dose of 0.5 g L−1 were found to be 181.9 mg g−1 and 90.95%, respectively, when MO concentration, temperature, pH and equilibrium time were 100 mg L−1, 298 K, 6.0 and 120 min, respectively. The isotherms showed that the adsorption of MO by Zn/Al-LDO was both consistent with Langmuir and Freundlich equations. The adsorption process was spontaneous and endothermic in nature and followed pseudo-second-order kinetic model. The calculated value ofEa was found to be 77.1 kJ mol−1, which suggests that the process of adsorption of methyl orange is controlled by the rate of reaction rather than diffusion. The possible mechanism for MO adsorption has also been presumed. In addition, the competitive anions on adsorption and the regeneration of Zn/Al-LDO have also been investigated.(a) The calcined layered double hydroxides. (b) The layered structure of recovered products is restructured by adsorption. (c) MO− intercalated into LDH layered by chemisorption.
Keywords: Calcined layered double hydroxides; Adsorption; Methyl orange; Thermodynamic parameters; Kinetics; Regeneration
Study of the growth process of in situ polyaniline deposited films
by Silmar A. Travain; Nara C. de Souza; Débora T. Balogh; José A. Giacometti (pp. 292-297).
Polyaniline (PAni) thin films were deposited onto BK7 glass substrates using the in situ deposition technique. The control of the time and the aniline concentration in the PAni polymerization reaction on the film deposition allowed us to prepare films with different thickness, down to ∼25 nm. The film growth process was monitored by measuring the UV–vis spectra and the AFM height profiles of the film surface. The curves of adsorption kinetics were analyzed with the Avrami's model, yielding an exponentn=3, thus indicating nucleation of spheroids at the initial stages of polymerization that grow through a diffusion process. AFM images of the surface height profiles corroborate this hypothesis, with spheroids growing with no preferred orientation during the in situ deposition.AFM image of in situ PAni film adsorbed for 90 min with a scanning window of2×2μm. Beside, the height profile of film and the average diameter vs average height of the aggregates for the in situ PAni films (solutions with concentrations of 0.022 mol/L).
Keywords: Polyaniline; Adsorption kinetics; Surface morphology
Physicochemical study of novel organoclays as heavy metal ion adsorbents for environmental remediation
by Panagiota Stathi; Kiriaki Litina; Dimitrios Gournis; Thomas S. Giannopoulos; Yiannis Deligiannakis (pp. 298-309).
Four organic-modified clays based on a SWy-2 montmorillonite were prepared by embedding ammonium organic derivatives with different chelating functionalities (NH2,COOH,SH orCS2) in the interlayer space of montmorillonite. Organic molecules such as (a) hexamethylenediamine, (b) 2-(dimethylamino)ethenethiol, (c) 5-aminovaleric acid and (d) hexamethylenediamine-dithiocarbamate were used for the clay modification in order to study the effect of the chelating functionality on heavy metal ions binding from aqueous solutions. The organoclays were characterized by powder X-ray diffraction (XRD), infrared (FTIR) and NMR spectroscopies. The experimental data showed that the organic molecules are intercalated into the interlamelar space with the long dimension parallel to the clay sheets. Their sorbing properties were evaluated for the removal of heavy metals, Pb, Cd and Zn, from aqueous solutions as a function of the pH. When compared with the unmodified SWy-2 montmorillonite, the modified clays show significant improvement in terms of sorbing selectivity as well as of metal loading capacity. The fit to adsorption data by a Surface Complexation Model shows that the intercalated molecules act as specific binding sites in the clay. These contribute additional sorption capacity which is additive to the variable charge edge-sites of the clay in competition with the permanent charge sites.
Keywords: Organoclay; Montmorillonite; SWy; Heavy metal; Environmental remediation; SCM; Surface charge; Cd; Pb; Zn; FITEQL
pH dependence of adsorption of n-dodecyl- β-d-maltoside on solids
by Shaohua Lu; Yu Bian; Lei Zhang; Ponisseril Somasundaran (pp. 310-316).
Adsorption of surfactants on solids plays an important role in industrial operations such as separation, lubrication, flotation, dispersion, chemical mechanical polishing, and enhanced oil recovery. In this work, adsorption of a typical biodegradable nonionic surfactant, n-dodecyl- β-d-maltoside, on solids was studied to explore its potential applications. Even though it is a nonionic surfactant, significant pH-dependence was revealed for the adsorption on alumina in the range from pH 4 to 7. The adsorption density was found to be proportional to the concentration of surfaceAlOH group amongAl(OH2)+ andAlO− groups. The equilibriums among the surface species are governed by pH through surface ionization reactions. The surfaceAlOH group evidently determines the formation of hydrogen bonding between the surfactant molecules and the solid surface and thus the adsorption. Similar correlation was also found in the case of hematite. The results help to understand the mechanism of adsorption of sugar-based surfactant on solids.The adsorption of n-dodecyl- β-d-maltoside on alumina was found to be significantly pH-dependent, which is attributed to the effects of surface hydroxyl species on the hydrogen bonding formation.
Keywords: Sugar-based surfactant; n; -Dodecyl-; β; -; d; -maltoside; Adsorption; Alumina; Hematite; Surface ionization
Appropriate volumes for adsorption isotherm studies: The absolute void volume, accessible pore volume and enclosing particle volume
by D.D. Do; H.D. Do (pp. 317-330).
In adsorption studies the choice of an appropriate void volume in the calculation of the adsorption isotherm is very crucial. It is often taken to be the apparent volume as determined by the helium expansion experiments. Unfortunately this method has difficulties especially when dealing with microporous solids, in which adsorption of helium might become significant at ambient temperatures. The amount adsorbed is traditionally obtained as the excess amount and the term “excess” refers to the excess over the amount occupying the apparent volume that has the same density as the bulk gas density. This could give rise to the maximum in the plot of excess amount versus pressure under supercritical conditions, and in some cases giving negative excess. Such behavior is difficult to analyze because the excess amount is not amenable to any classical thermodynamic treatments. In this paper we will present a method to determine the absolute void volume, and in that sense this volume is independent of temperature and adsorbate. The volume that is accessible to the centers of gas molecules is also investigated, and it is called the accessible volume. This volume depends on the choice of adsorbate, and it is appropriate to use this volume to calculate the pore density because we can assess how dense the adsorbed phase is. In the quest to determine the “absolute” adsorption isotherm so that a thermodynamics analysis can be applied, it is necessary to introduce the concept of “enclosing” volume, which is essentially the volume that encloses all solid particles, including all void spaces in them. The amount adsorbed is defined by the number of molecules residing in this volume. Having these volumes, we can derive the geometrical accessible void volume inside the particle and the solid volume, from which the particle and solid densities can be calculated.
Keywords: Adsorption; Void volume; Isotherm; Excess
Alternating bioactivity of multilayer thin films assembled from charged derivatives of chitosan
by Somruethai Channasanon; Wilaiporn Graisuwan; Suda Kiatkamjornwong; Voravee P. Hoven (pp. 331-343).
Charged derivatives of chitosan, N-sulfofurfuryl chitosan (SFC) and N-[(2-hydroxyl-3-trimethylammonium)propyl]chitosan chloride (HTACC) were prepared by reductive alkylation of amino groups of chitosan (CHI) using 5-formyl-2-furansulfonic acid, sodium salt (FFSA) as a reagent and ring opening of glycidyltrimethylammonium chloride (GTMAC) by amino groups of chitosan, respectively. The chemical structures of the charged derivatives were verified by1H NMR and FTIR analyses. Multilayer assembly of SFC, HTACC, CHI and the selected oppositely charged polyelectrolytes was monitored by a quartz crystal microbalance (QCM). Stratification of the multilayer film fabricated on plasma-treated poly(ethylene terephthalate) (treated PET) substrate was demonstrated by water contact angle data. The coverage of the assembled films was characterized by AFM and ATR-FTIR analyses. The bioactivity of the deposited multilayer film on the treated PET substrate was tested against selected proteins having a distinctive size and charge. This research strongly suggests that both SFC and HTACC are potential candidates for altering the surface bioactivity of materials. N-sulfofurfuryl chitosan (SFC) and N-[(2-hydroxyl-3-trimethylammonium)propyl]chitosan chloride (HTACC) are capable of forming multilayer film similar to chitosan (CHI).
Keywords: Chitosan; Charged derivative; Layer-by-layer adsorption; Multilayer film; Polyelectrolyte; Protein adsorption
The reorientation of poly(2-dimethylamino ethyl methacrylate) after environment stimuli improves hydrophilicity and resistance of protein adsorption
by Yan-Lei Su; Chao Li (pp. 344-349).
There is a dense poly(2-dimethylamino ethyl methacrylate) (PDMAEMA) layer on the surface of poly(acrylonitrile and 2-dimethylamino ethyl methacrylate) (PAN-DMAEMA) membrane. The contact angle measurement indicated that the hydrophilicity of membrane increases at higher pH value and ionic strength. The reorientation of PDMAEMA after environment stimuli results in further enrichment of ester groups on the membrane surface according to XPS analysis. The amount of adsorbed bovine serum albumin (BSA) on PAN-DMAEMA membrane is dramatically decreased at higher pH value and ionic strength. A viewpoint based on the minimizing electrostatic interactions between PDMAEMA groups after environment stimuli leading to the conformation switch of PDMAEMA chains from stretched to shrunk states, which results in higher surface enrichment of ester groups enhancing hydrophilic property of the PAN-DMAEMA membrane, was put forward to explain the resistance of protein adsorption on the membrane.The reorientation of PDMAEMA and the existence of exchanged ions make the membrane more hydrophilic, so that BSA adsorption is remarkably decreased at higher pH value and ionic strength.
Keywords: Membrane; Protein adsorption; Hydrophilicity; Antifouling
Interaction between lysozyme and poly(acrylic acid) microgels
by Christian Johansson; Per Hansson; Martin Malmsten (pp. 350-359).
The interaction between lysozyme and oppositely charged poly(acrylic acid) microgels was investigated by micromanipulator-assisted light microscopy, confocal microscopy and circular dichroism. Lysozyme uptake and distribution within the microgel particles, and its effect on microgel deswelling, was studied regarding effects of pH, ionic strength and lysozyme concentration. For a range of conditions, lysozyme distributes nonuniformly within the microgels, forming a lysozyme/microgel shell in the outer parts of the microgel. This shell formation is associated both with increased lysozyme loading to the microgels and with increased lysozyme-induced microgel deswelling. At high microgel charge density, the shell formation displays nonmonotonic ionic strength dependence. The shells formed are characterized by a net positive charge, and by relatively fast exchange of lysozyme between shell and solution, although the exchange kinetics decreases strongly with decreasing ionic strength. At conditions of slower exchange kinetics, the shells are characterized by an effective pore size of less than about 4 nm.Studies on lysozyme uptake into lightly cross-linked poly(acrylic acid) microgels, have shown that pronounced lysozyme-induced deswelling is associated with the formation of a lysozyme-rich surface-phase.
Keywords: Confocal; Microscopy; Lysozyme; Microgel; Poly(acrylic acid); Surface phase; Shell formation; Phase separation
Characterization and evaluation of the hydrolytic stability of trifluoroacetylated cellulose fibers
by Ana G. Cunha; Carmen S.R. Freire; Armando J.D. Silvestre; Carlos Pascoal Neto; Alessandro Gandini; Elina Orblin; Pedro Fardim (pp. 360-366).
The controlled heterogeneous modification of cellulose fibers with trifluoroacetic anhydride was investigated. The characterization of the ensuing materials was performed by elemental analysis, FTIR spectroscopy, X-ray diffraction (XRD), thermogravimetry, and surface analysis (XPS, ToF-SIMS, and contact angles measurements). The trifluoroacetylation enhanced significantly the hydrophobic and lipophobic character of the fibers, whereas their thermal stability and cristallinity were only modestly affected by this treatment, except under the most severe conditions for the latter. Their hydrolytic stability to water vapour was also assessed as a function of the air humidity and shown to be lower than that of still liquid water in the case of a saturated atmosphere.It is possible to transform the surface of cellulose fibers from very hydrophilic to highly hydrophobic and lipophobic and to make them regain their pristine properties by a simple hydrolytic treatment.
Keywords: Cellulose; Trifluoroacetic anhydride; Trifluoroacetates; Hydrophobic; Lipophobic; Hydrolysis
Microgel particles containing methacrylic acid: pH-triggered swelling behaviour and potential for biomaterial application
by Sarah Lally; Paul Mackenzie; Christine L. LeMaitre; Tony J. Freemont; Brian R. Saunders (pp. 367-375).
pH-responsive microgels are crosslinked polymer particles that swell when the pH approaches thepKa of the ionic monomer incorporated within the particles. In recent work from our group it was demonstrated that the mechanical properties of degenerated intervertebral discs (IVDs) could be restored to normal values by injection of poly(EA/MAA/BDDA) (ethylacrylate, methacrylic acid and butanediol diacrylate) microgel dispersions [J.M. Saunders, T. Tong, C.L. Le Maitre, T.J. Freemont, B.R. Saunders, Soft Matter 3 (2007) 486]. In this work we report the pH dependent swelling and rheological properties of poly(MMA/MAA/EGDMA) (methylmethacrylate and ethyleneglycol dimethacrylate) microgel dispersions. This system was investigated because it contains monomers that are already used as biomaterials. The poly(MMA/MAA/EGDMA) particles exhibit pH-triggered volume swelling ratios of up to ca. 250. The swelling onset for these particles occurs at pH values greater than ca. 6.0. ApKa for these particles of ca. 6.7 is consistent with titration and swelling data. Fluid-to-gel phase diagrams for concentrated poly(MMA/MAA/EGDMA) dispersions were determined as a function of polymer volume fraction and pH using tube-inversion measurements. The rheological properties for the gelled microgel dispersions were investigated using dynamic rheology measurements. The elastic modulus data for the poly(MMA/MAA/EGDMA) gelled dispersions were compared to data for poly(EA/MAA/BDDA) microgels. A similar pH-dependence for the elastic modulus was apparent. The maximum elastic modulus was achieved at a pH of about 7.0. The elastic modulus is an exponentially increasing function of polymer volume fraction at pH 7.0. Preliminary cell challenge experimental data are reported that indicate that gelled poly(MMA/MAA/EGDMA) microgel dispersions are biocompatible with cells from human intervertebral discs. However, the duration over which these experiments could be performed was limited by gradual redispersion of the gelled microgel dispersions. Based on the results presented it is suggested that poly(MMA/MAA/EGDMA) microgel would be a good candidate as a biomaterial for structural support of soft connective tissues.This work investigates the pH-dependent swelling and rheological properties of microgel particles containing methacrylic acid. The results provide insight into the structure–property relationships for the particles and establishes a basis for their potential use as a load supporting biomaterial.
Keywords: Microgel; Responsive polymer; Gel; Biocolloid; Intervertebral disc
Nanoscale conformational ordering in polyanilines investigated by SAXS and AFM
by Fabio L. Leite; Mario de Oliveira Neto; Leonardo G. Paterno; Michel R.M. Ballestero; Igor Polikarpov; Yvonne P. Mascarenhas; Paulo S.P. Herrmann; Luiz H.C. Mattoso; Osvaldo N. Oliveira Jr. (pp. 376-387).
Understanding the adsorption mechanisms in nanostructured polymer films has become crucial for their use in technological applications, since film properties vary considerably with the experimental conditions utilized for film fabrication. In this paper, we employ small-angle X-ray scattering (SAXS) to investigate solutions of polyanilines and correlate the chain conformations with morphological features of the nanostructured films obtained with atomic force microscopy (AFM). It is shown that aggregates formed already in solution affect the film morphology; in particular, at early stages of adsorption film morphology appears entirely governed by the chain conformation in solution and adsorption of aggregates. We also use SAXS data for modeling poly( o-ethoxyaniline) (POEA) particle shape through an ab initio procedure based on simulated annealing using the dummy atom model (DAM), which is then compared to the morphological features of POEA films fabricated with distinct pHs and doping acids. Interestingly, when the derivative POEA is doped with p-toluene sulfonic acid (TSA), the resulting films exhibit a fibrillar morphology—seen with atomic force microscopy and transmission electron microscopy—that is consistent with the cylindrical shape inferred from the SAXS data. This is in contrast with the globular morphology observed for POEA films doped with other acids.The polyaniline molecules in solution present a coiled structure (less-packed) when in pH 3, which indicates a more extended structure, while at pH 10 blobs are formed. The figures show the low-resolution particles shape determined from the experimental data using the ab initio procedure.
Keywords: Self-assembly; SAXS; AFM; TEM; Nanostructures; Thin films; PANI; Adsorption and conformation
Langmuir–Blodgett films of cellulose nanocrystals: Preparation and characterization
by Youssef Habibi; Laurence Foulon; Véronique Aguié-Béghin; Michaël Molinari; Roger Douillard (pp. 388-397).
The goal of this work is the preparation of monolayers of cellulose I nanocrystals providing flat crystalline cellulose surfaces. Suspensions of cellulose nanocrystals were prepared by hydrolyzing ramie and tunicin fibers with sulfuric acid. Due to surface grafted sulfate groups, the negatively charged, rod-like cellulose nanocrystals were found to form stable layers at the air–water interface in the presence of a cationic amphiphilic molecule such as dioctadecyldimethylammonium (DODA) used in this work. These layers were formed at different cellulose–DODA weight ratios, compressed and analyzed by tensiometry, ellipsometry and Brewster angle microscopy. At low cellulose concentrations the layers are discontinuous, becoming dense and homogeneous upon reaching a critical weight ratio, which depends on the aspect ratio of the cellulose nanocrystals. After transfer onto silicon wafers, the surface composition and morphology as well as the thickness of the films were examined by X-ray photoelectron spectroscopy, ellipsometry and atomic force microscopy. The results indicate that they are monolayer films, well structured, relatively smooth and pure. These films offer a crystalline and easily reproducible model cellulose surface.
Keywords: Cellulose model; Cellulose nanocrystals; Langmuir–Blodgett film; Ellipsometry; Brewster angle microscopy
Synthesis, size control and fluorescence studies of gold nanoparticles in carboxymethylated chitosan aqueous solutions
by Ling Huang; Maolin Zhai; Jing Peng; Ling Xu; Jiuqiang Li; Genshuan Wei (pp. 398-404).
A facile ultraviolet (UV) light irradiation method to synthesize gold nanoparticles (AuNPs) in the alkalic carboxymethylated chitosan (CM-chitosan) solution was first proposed in this paper. CM-chitosan, a water soluble polysaccharide derivative, served as both reducing agent for gold cations and stabilizing agent for AuNPs. The pH, the concentration of HAuCl4 and irradiation time had obvious influence on the size, amount and morphology of AuNPs, which traced by UV–visible spectrometer and high resolution transmission electron microscopy. AuNPs synthesized in this method can be dispersed stably in alkalic CM-chitosan solution for more than 6 months. The possible stability mechanism of AuNPs was discussed based on the change of carboxyl group of CM-chitosan chain with pH and FTIR analyses. XRD pattern confirmed the cubic crystal structure of AuNPs. The fluorescence emission band of AuNPs with an excitation wavelength of 316 nm can be observed at 400 nm, which was affected remarkably by irradiation time and concentration of HAuCl4.A facile ultraviolet light irradiation method to synthesize gold nanoparticles in the alkalic carboxymethylated chitosan solution (pH 12.4) was first proposed.
Keywords: Gold nanoparticles; Carboxymethylated chitosan; UV light irradiation; Surface plasmon band; Fluorescence
Self-assembly of β-casein and lysozyme
by Xiaoyun Pan; Shaoyong Yu; Ping Yao; Zhengzhong Shao (pp. 405-412).
The self-assembly of β-casein and lysozyme, a linear and a globular protein with isoelectric point of pH 5.0 and 10.7, respectively, was studied. Polydisperse electrostatic complex micelles formed when mixing β-casein and lysozyme aqueous solutions. After the micelle solution was heated, lysozyme gelated and β-casein was trapped in the gel, producing narrowly dispersed nanoparticles. The nanoparticles were characterized with laser light scattering, ζ-potential, steady state fluorescence, atomic force microscopy, and transmission electron microscopy. The nanoparticles have spherical shape and their sizes depend on the pH of the heat treatment and the molar ratio of β-casein to lysozyme. The nanoparticles display amphoteric property and are relatively hydrophobic at pH around 5 and around 10. The net charges on the surface stabilize the nanoparticles in the solution.
Keywords: β; -Casein; Lysozyme; Electrostatic complex; Nanoparticle; Self-assembly
Circular dichroism analysis of penicillin G acylase covalently immobilized on silica nanoparticles
by Bertolt Kranz; Jochen Bürck; Matthias Franzreb; Rainer Köster; Anne S. Ulrich (pp. 413-419).
Circular dichroism (CD) was used to characterize the secondary structure of penicillin G acylase upon covalent immobilization on silica nanoparticles. Covalent immobilization was achieved by functionalizing the silica nanoparticles with glutardialdehyde and coupling to the free NH2 groups of the enzyme (lysine and arginine side chains). The loading of the covalently bound enzyme was increased up to saturation, which was reached at 54.6 mg immobilized enzyme per g silica nanobeads. For structural characterization of the commercially available enzyme its exact molecular mass was determined by mass spectrometry in order to enable precise evaluation of the CD data. The fraction of secondary structure elements of the free and immobilized enzyme were estimated from the respective CD spectra using standard algorithms (CONTINLL, CDSSTR, SELCON3). The fractions obtained by the different algorithms for the free enzyme agreed well with one another and also with data from X-ray diffraction described in the literature. Interestingly, the secondary structure fractions found for the immobilized enzyme were very similar to the free enzyme and nearly constant over all experiments. These results indicate that even a loading of up to 55.8 mg/g (enzyme per silica nanoparticles) causes only slight structural changes. However, the specific activity determined by a kinetic assay decreased by around 60%, when increasing the loading from 14.9 to 55.8 mg/g. Because of the fact that we found no major changes in the secondary structure, diffusion limitation seems to be the main reason for the decline of the specific activity.Bio-functionalization of silica nanoparticles was performed by covalent binding of penicillin G acylase. Structure–function analysis of free and bound enzyme using CD and activity tests revealed only minimal changes in secondary structure but an up to 80% decrease in specific activity upon immobilization. This may be caused rather by diffusion limitation than by a conformational change of the enzyme.
Keywords: Penicillin G acylase; Silica nanoparticles; Covalent immobilization; Circular dichroism; Secondary structure deconvolution; Specific enzyme activity
Encapsulation of emitting CdTe QDs within silica beads to retain initial photoluminescence efficiency
by Ping Yang; Masanori Ando; Norio Murase (pp. 420-427).
Highly luminescent silica beads (30 nm–2 μm ∅) incorporating CdTe quantum dots (QDs) were prepared via a two-step preparation procedure, namely a modified Stöber synthesis and a subsequent reverse micelle route. In the modified Stöber synthesis, the silica molecules are deposited on the surface of the QDs. After this first step, these coated QDs were incorporated into silica beads via a reverse micelle route. Inductively coupled plasma analysis revealed a red-emitting silica bead of 30 nm in diameter thus prepared encapsulated roughly 14 CdTe QDs. These glass beads (30–40 nm ∅) retained the initial photoluminescence (PL) efficiencies of the colloidal QDs (27 and 65% for the green- and red-emitting beads, respectively). The protection of QDs by a silica layer at the first step, together with the short total reaction time, is the main reason for the retention of the PL efficiency. The size of the glass beads can be easily controlled over the wide range by adjusting the injection speed and the ratio of chemicals used for the reverse micelle preparation. Since the original efficiency was maintained in the beads and is the highest ever reported for QD-containing silica beads, the method presented here is of significant importance for applications of silica beads to biological probes.SiO2 beads incorporating emitting CdTe QDS revealed high PL efficiency (65%) via a two-step synthesis. The high PL efficiency of the beads opens up new possibilities for various applications.
Keywords: CdTe; Nanocrystals; Silica bead; Luminescence
Analysis of the aggregation–fragmentation population balance equation with application to coagulation
by Matthäus U. Bäbler; Massimo Morbidelli (pp. 428-441).
Coagulation of small particles in agitated suspensions is governed by aggregation and breakage. These two processes control the time evolution of the cluster mass distribution (CMD) which is described through a population balance equation (PBE). In this work, a PBE model that includes an aggregation rate function, which is a superposition of Brownian and flow induced aggregation, and a power law breakage rate function is investigated. Both rate functions are formulated assuming the clusters are fractals. Further, two modes of breakage are considered: in the fragmentation mode a particles splits intow⩾2 fragments of equal size, and in the erosion mode a particle splits into two fragments of different size. The scaling theory of the aggregation–breakage PBE is revised which leads to the result that under the negligence of Brownian aggregation the steady state CMD is self-similar with respect to a non-dimensional breakage coefficient θ. The self-similarity is confirmed by solving the PBE numerically. The self-similar CMD is found to deviate significantly from a log–normal distribution, and in the case of erosion it exhibits traces of multimodality. The model is compared to experimental data for the coagulation of a polystyrene latex. It is revealed that the model is not flexible enough to describe coagulation over an extended range of operation conditions with a unique set of parameters. In particular, it cannot predict the correct behavior for both a variation in the solid volume fraction of the suspension and in the agitation rate (shear rate).A PBE model for aggregation and breakage is investigated. The model leads to a self-similar CMD with respect to a breakage coefficient. The model is compared to a set of exclusive experimental data.
Keywords: Colloidal clusters; Aggregation; Breakage; Turbulent coagulation; Population balance equation; Self-similarity; Scaling
Effect of microemulsion variables on copper oxide nanoparticle uptake by AOT microemulsions
by Nashaat N. Nassar; Maen M. Husein (pp. 442-450).
Ultradispersed metal oxide nanoparticles have applications as heterogeneous catalysts for organic reactions. Their catalytic activity depends primarily on their surface area, which in turn, is dictated by their size, colloidal concentration and stability. This work presents a microemulsion approach for in situ preparation of ultradispersed copper oxide nanoparticles and discusses the effect of different microemulsion variables on their stability and highest possible time-invariant colloidal concentration (nanoparticle uptake). In addition, a model which describes the effect of the relevant variables on the nanoparticle uptake is evaluated. The preparation technique involved solubilizing CuCl2 in single microemulsions followed by direct addition of NaOH. Upon addition of NaOH, copper hydroxide nanoparticles stabilized in the water pools formed in addition to a bulk copper hydroxide precipitate at the bottom. The copper hydroxide nanoparticles transformed with time into copper oxide. After reaching a time-independent concentration, mixing had limited effect on the nanoparticle uptake and particle size. Particle size increased with increasing the surfactant concentration, concentration of the precursor salt, and water to surfactant mol ratio; while the nanoparticle uptake increased linearly with the surfactant concentration, displayed an optimum with R and a power function with the concentration of the precursor salt. Surface areas per gram of nanoparticles were much higher than literature values. Even though lower area per gram of nanoparticles was obtained at higher uptake, higher surface area per unit volume of the reverse micellar system was attained. A model based on water uptake by Wisor type II microemulsions, and previously used to describe iron oxide nanoparticle uptake by the same microemulsions, agreed well with the experimental results.
Keywords: Nanoparticle; Copper oxide; Microemulsion; Surfactant; Catalyst; Surface area; Uptake; Model
The Hamaker constant of anatase aqueous suspensions
by A.I. Gómez-Merino; F.J. Rubio-Hernández; J.F. Velázquez-Navarro; F.J. Galindo-Rosales; P. Fortes-Quesada (pp. 451-456).
The linear relationship of the yield stress with the square zeta potential may be used to determine the Hamaker constants in suspensions. In this work we have obtained the Hamaker constant for the attractive forces between anatase particles in aqueous suspensions using this method and compared them with those obtained by contact angle measurement. The results show excellent agreement.The linear relationship of the yield stress with the squared ζ potential may be used to determine the Hamaker constant in suspensions. In this work we have obtained the Hamaker constant for the attractive force between anatase particles in aqueous suspensions using this method, and compared it with those obtained by contact angle measurement. The results show an excellent agreement.
Keywords: Hamaker constant; Anatase; Yield stress; Zeta potential; Contact angle
Surface analysis of cryofixation-vacuum-freeze-dried polyaluminum chloride–humic acid (PACl–HA) flocs
by Yili Wang; Baiyu Du; Jie Liu; Jia Lu; Baoyou Shi; Hongxiao Tang (pp. 457-466).
The powder of polyaluminum chloride–humic acid (PACl–HA) flocs was prepared by cryofixation-vacuum-freeze-drying method. The FTIR spectra show that some characteristic functional groups in polyaluminum chloride (PACl), humic acid (HA), and kaolin still existed in the dried flocs. X-ray diffractometry (XRD) patterns indicate that these flocs are amorphous. Nitrogen adsorption–desorption isotherms were obtained for different samples of the dried PACl–HA flocs. The BET specific surface area, BJH cumulative absorbed volume and BJH desorption average pore diameter of them were determined. The peak values of 8.4–11.2 nm (pore diameter) for pore size distribution (PSD) curves indicate that the pores of the dried flocs are mostly mesopores. The surface fractal dimensionsDs and the corresponding fractal scales determined from both SEM images and nitrogen adsorption–desorption data sets reveal the multi-scale surface fractal properties of the dried PACl–HA flocs, which exhibited two distinct fractal regimes: a regime of low fractal dimensions (2.07–2.26) at higher scales (23–387 nm), mainly belonging to exterior surface scales, and a higher fractal dimensions (2.24–2.37) at lower scales (0.80–7.81 nm), falling in pore surface scales. Both HA addition and kaolin reduction in dried floc can decrease the irregularity and roughness of external surface. However, for the irregularity and roughness of pore surface, the addition of HA or kaolin in dried floc can increase them. Furthermore, some difference was found between the pore surface fractal dimensionsDs calculated from nitrogen adsorption and desorption data. The pore surfaceDs values calculated through thermodynamic model were much greater than three.Two distinct fractal regimes in the surface of the dried PACl–HA flocs: a regime of low fractal dimensions at higher scales and a higher fractal dimensions at lower scales.
Keywords: Abbreviations; PACl–HA; polyaluminum chloride–humic acid; PACl; polyaluminum chloride; HA; humic acid; XRD; X-ray diffractometry; PSD; pore size distribution; SEM; scanning electron microscope; D; s; surface fractal dimensions; NOM; natural organic matter; DBPs; disinfection by-products; THMs; trihalomathanes; HAAs; haloacetic acids; BAT; best available technology; IPFs; inorganic polymer flocculants; FHH; Frenkel–Halsey–Hill; DAF; dissolved air flotation; JMS; jet mixed separator; HRT; hydraulic retention timeCryofixation-vacuum-freeze-drying; Polyaluminum chloride (PACl); Humic acid; Floc structure; Surface fractal analysis
Interaction of colloidal particles ofNH4+-montmorillonite with activated carbon
by Eladio A. Ferreiro; Silvia G. de Bussetti (pp. 467-475).
The interaction between negative colloidal particles ofNH4+-montmorillonite and particles of activated carbon was studied as a function of particle concentration, pH, and time of contact. The results show that carbon particles act as a support/bridge for clay particles, the type of resulting clay/carbon/clay associations depending on the pH and the clay/carbon ratio in the system. The relation between clay and carbon particles can be described by equations of the Langmuir type. For the same carbon particle concentration in the system, the relation varies from 6820 to 36,100 and is dependent on pH. The interaction coefficients at pH 6.5 correspond to reaction of pseudo-first (k1=4.14×10−3 to1.93×10−3 s−1) and pseudo-second order (k2=9.36×10−14 to2.47×10−14 cm3s−1) for different clay/carbon ratios. By using the Dubinin–Radushkevich equation, the interaction energy (±22.42, ±685.0, and ±14.63 J mol−1) was obtained for three different pH values (5, 6.7, and 7.6), demonstrating that the reaction is mainly physical.The interaction was studied between the negative colloidal particles ofNH4+-montmorillonite and the particles of activated carbon as a function of particle concentration, pH, and time of contact. The results show that carbon particles act as a support/bridge to clay particles, the type of resulting clay/carbon/clay associations depending on the pH and the clay/carbon ratio in the system. The relation between clay and carbon particles can be described by equations of the Langmuir type.
Keywords: Activated carbon; Adsorption; Kinetics of interaction; Montmorillonite; Particle interaction
One-step synthesis of gold nanoparticles using azacryptand and their applications in SERS and catalysis
by Kang Yeol Lee; Jaeyoung Hwang; Young Wook Lee; Jineun Kim; Sang Woo Han (pp. 476-481).
A new aqueous-phase method for the preparation of stable gold nanoparticles by using 1,4,7,10,13,16,21,24-octaazabicyclo[8.8.8]hexacosane (azacryptand) as both reductant and stabilizer is reported. Reduction of HAuCl4 with azacryptand at room temperature yields nano-sized particles within a short time. The obtained gold nanoparticles have been characterized by UV–vis spectroscopy, transmission electron microscopy, and X-ray diffraction. Comparison of FT-IR spectra of azacryptand before and after reaction revealed that azacryptand molecules reduce gold ions as the amino moieties in the molecules are oxidized to imino groups. The prepared gold nanoparticles show efficient surface-enhanced Raman scattering properties and can effectively catalyze reduction of 4-nitrophenol by sodium borohydride in aqueous solution.
Keywords: Gold nanoparticles; Azacryptand; Interface; SERS; Catalysis
Relative importance of hydrolyzed Al(III) species (Ala, Alb, and Alc) during coagulation with polyaluminum chloride: A case study with the typical micro-polluted source waters
by Mingquan Yan; Dongsheng Wang; Jiuhui Qu; Wenjie He; Christopher W.K. Chow (pp. 482-489).
The relative importance of three different Al species, Ala (monomeric species, instantaneous reacted species), Alb (medium polymer species, reacted less than 120 min), and Alc (colloidal or solid species, no reaction), defined by timed complexation reaction rate measured by using ferron reagent in polyaluminum chloride (PACl) was investigated in terms of DOC (dissolved organic carbon), UV254, and turbidity removal efficiencies. Micro-polluted, typical North China, source waters were used to conduct the experiments. The results show that DOC removal is correlated well to the content of Alb. Removal of UV254 is determined by the content of Alb and Alc, particularly Alc. Turbidity removal is primarily related to the content of Alc; however, Alb could destabilize particles efficiently, and the flocs formed by Alb are not as large as those formed by Alc, which affected the settling efficiency. Unlike the preformed Alb, the in situ formed Alb could remove turbidity more efficiently since Alc is the dominant final species formed during coagulation. Ala shows a strong ability to react with some unsatisfied coordinate bonds of organic matter to facilitate particle and DOC removal. The distinct coagulation feature of Ala, Alb, and Alc can be applied to develop tailor-made PACl (with the correct distribution of Al species) to match the characteristics of raw water for optimized coagulation.
Keywords: Optimized coagulation; PACl; Speciation; Organic matter; pH control
Counterion volume effects in mixed electrical double layers
by P.M. Biesheuvel; M. van Soestbergen (pp. 490-499).
When a monolayer of negatively charged surfactant molecules is brought in contact with an aqueous solution containing mixtures of counterions of different size and valency, very large deviations from Poisson–Boltzmann theory (PBT) develop at a high surface charge, with the smaller counterion outcompeting the larger one (even if divalent) near the interface, leading to counterion segregation [V.L. Shapovalov, G. Brezesinski, J. Phys. Chem. B 110 (2006) 10032]. We use a modified PBT that empirically includes an extended Carnahan–Starling equation-of-state to describe hard-sphere interactions in electrical double layers containing ions of different size and charge. Model calculations are made for ion concentration profiles, free energies, surface pressures, and differential capacities. At high surface charge, volume interactions become important, leading to significant deviations from PBT. In contrast to PBT, at high surface charge, contributions to energy and pressure are no longer mainly entropic, but instead volume and electrostatic field effects now dominate. When the hydrated size of the divalent ion is used as an adjustable parameter, the theory is in good agreement with the experimental data.In a mixture of ions of different hydrated size, at high enough surface charge, larger divalent ions are expelled from the interface by smaller counterions.
Keywords: Poisson–Boltzmann theory; Electrostatic double layer; Surfactant monolayer; Volume effects
Cryo-SEM studies of latex/ceramic nanoparticle coating microstructure development
by Hui Luo; L.E. Scriven; Lorraine F. Francis (pp. 500-509).
Cryogenic scanning electron microscopy (cryo-SEM) was used to investigate microstructure development of composite coatings prepared from dispersions of antimony-doped tin oxide (ATO) nanoparticles (∼30 nm) or indium tin oxide (ITO) nanoparticles (∼40 nm) and latex particles (polydisperse,Dv: ∼300 nm). Cryo-SEM images of ATO/latex dispersions as-frozen show small clusters of ATO and individual latex particles homogeneously distribute in a frozen water matrix. In contrast, cryo-SEM images of ITO/latex dispersions as-frozen show ITO particles adsorb onto latex particle surfaces. Electrostatic repulsion between negatively charged ATO and negatively charged latex particles stabilizes the ATO/latex dispersion, whereas in ITO/latex dispersion, positively charged ITO particles are attracted onto surfaces of negatively charged latex particles. These results are consistent with calculations of interaction potentials from past research. Cryo-SEM images of frozen and fractured coatings reveal that both ceramic nanoparticles and latex become more concentrated as drying proceeds; larger latex particles consolidate with ceramic nanoparticles in the interstitial spaces. With more drying, compaction flattens the latex–latex particle contacts and shrinks the voids between them. Thus, ceramic nanoparticles are forced to pack closely in the interstitial spaces, forming an interconnected network. Finally, latex particles partially coalesce at their flattened contacts, thereby yielding a coherent coating. The research reveals how nanoparticles segregate and interconnect among latex particles during drying.Steps in preparation and cryo-SEM characterization of a partially dried coating.
Keywords: Cryo-SEM; Microstructure development; Dispersion; Coating; Ceramic nanoparticle; Latex; Drying
Morphology, structure, and magnetism of FeCo thin films electrodeposited on hydrogen-terminated Si(111) surfaces
by J. Zarpellon; H.F. Jurca; N. Mattoso; J.J. Klein; W.H. Schreiner; J.D. Ardisson; W.A.A. Macedo; D.H. Mosca (pp. 510-516).
In this work we describe the fabrication of FeCo alloy (less than 10 at% Co) thin films from aqueous ammonium sulfate solutions onto n-type Si(111) substrates using potentiostatic electrodeposition at room temperature. The incorporation of Co into the deposits tends to inhibit Fe silicide formation and to protect deposits against oxidation under air exposure. As the incorporation of Co was progressively increased, the sizes of nuclei consisting of FeCo alloy increased, leading to films with a highly oriented body-centered cubic structure with crystalline texture, where (110) planes remain preferentially oriented parallel to the film surface.Surface morphology of FeCo thin films (less than 10 at% Co) electrodeposited on Si(111) consists of juxtaposed aggregates with a body-centered cubic structure.
Keywords: FeCo thin films; Electrodeposition on Si; Magnetic properties and microstructure; X-ray photoelectron spectroscopy; Mössbauer spectroscopy
Accelerated direct electrochemistry of hemoglobin based on hemoglobin–carbon nanotube (Hb–CNT) assembly
by Renyun Zhang; Xuemei Wang; Kwok-Keung Shiu (pp. 517-522).
In this study, we have demonstrated that hemoglobin can be coupled to acid-treated multiwall carbon nanotubes in the presence of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and assembled as hemoglobin–carbon nanotube (Hb–CNT) composites. Our observations of the electrochemical studies demonstrate that the electrochemical response of Hb–CNT assembled in the presence of EDC is much higher than that in the absence of EDC. It is evident that the direct electron transfer of hemoglobin could be effectively accelerated in the Hb–CNT assembly by using EDC on a glassy carbon electrode (GCE), and the relative electron transfer rate constantKs is found to be1.02±0.05s−1. The results of our studies illustrate that the assembly of hemoglobin–multiwall carbon nanotubes using EDC could provide a novel strategy to effectively facilitate the direct electrochemistry of heme-containing proteins, which could be further utilized as a promising biosensor for some specific biological substrate and related biological process.A new strategy to effectively facilitate facilitating the direct electrochemistry of hemoglobin is based on the covalently associated Hb–CNT assembly by using EDC.
Keywords: Carbon nanotubes; Hemoglobin; Chemically modified electrode; Nanotechnology; Electrochemistry
Effect of granular activated carbon on degradation of methyl orange when applied in combination with high-voltage pulse discharge
by Yanzong Zhang; Jingtang Zheng; Xianfeng Qu; Honggang Chen (pp. 523-530).
The application of a gas–liquid series electrical discharge reactor for the degradation of methyl orange (MO) in the presence of granular activated carbon (GAC1V, GAC2V, and GAC3V) was investigated and the effect of these GACs in a combined treatment was evaluated, respectively. Under the experimental conditions used in this work, MO cannot be removed completely by GAC adsorption; the MO degradation is faster by pulse discharge, but satisfactory removal of chemical oxygen demand (COD) is never achieved. The MO degradation can be increased and COD can be removed effectively in the combined treatment through both the adsorption and the catalysis of GAC. The synergy intensity value indicates that a high correlation exists between the catalytic effect of GACs and the number of basic groups on their surface. Boehm titration and FTIR studies indicate that both acidic and basic groups on the GAC surface can be increased except that basic groups of GAC2V are slightly decreased by this process. This process can also slightly decrease their surface area and micropore and macropore volume. Furthermore, the virgin and saturated GAC samples can both be regenerated in situ after repeated use.The degradation of methyl orange could be increased significantly in the combined treatment through both the adsorption and the catalysis of GAC1V/GAC2V/GAC3V.
Keywords: Pulse discharge; COD removal; Granular activated carbon; Adsorption; Catalytic effect; Regeneration
Investigation of pyrite oxidation by hexavalent chromium: Solution species and surface chemistry
by Frédéric Demoisson; Martine Mullet; Bernard Humbert (pp. 531-540).
Pyrite oxidation processes by aqueous Cr(VI) were investigated at 25 °C under an argon atmosphere. Synthetic pyrite suspensions (6 g L−1) were reacted for 20 h with a range of Cr(VI) solutions from 0 to 700 μM and at pH 2–12. The main objective of this work was to investigate the reaction mechanisms by emphasizing the role of sulfur species. Aqueous chemical processes were well illustrated in acidic media where significant amounts of sulfate and iron species were determined. Sulfate anions are the final stable sulfur species involved in the reaction pathway. Experiments showing complete Cr(VI) removal from solution displayed ratios [S(VI)]/[Fe]tot<2, probably due to a deficit in aqueous sulfur species. Experiments showing incomplete Cr(VI) removal displayed ratios [Cr(VI)]removed/[S(VI)] close to 1.5. This ratio was found to be consistent with the formation of thiosulfate (S2O2−3). Thiosulfate ions disproportionated into elemental sulfur S(0) and tetrathionate ions (S4O2−6) that were finally oxidized to sulfate anions under acidic conditions. The distribution of the oxidation state of sulfur atoms at the pyrite surface determined by XPS was additional evidence for the multistep sulfur oxidation process. The presence of elemental sulfur in the S(2p) spectra correlated well with the disproportion of thiosulfate under acidic conditions.Pyrite oxidation by aqueous Cr(VI) is investigated by using XPS and solution analyses. Distribution of the oxidation state of sulfur atoms at the reacted surface is illustrated in the S(2p) spectrum.
Keywords: Pyrite; Oxidation; X-ray photoelectron spectroscopy (XPS); Chromium; Sulfate
Surface characterization and catalytic evaluation of manganese nodule leached residue toward oxidation of benzene to phenol
by K.M. Parida; Saswati Soumya Dash (pp. 541-546).
Water washed manganese nodule leached residue (WMNLR) calcined at different temperatures was characterized by XRD, FTIR, TG-DTA, surface area, surface oxygen, and surface acid sites. Surface area, surface oxygen, surface hydroxyl group, and surface acid sites increase up to 400 °C and then decrease with further rise in calcination temperature up to 700 °C. The catalytic activity of the calcined samples was tested for single-step oxidation of benzene to phenol using hydrogen peroxide as the oxidant and acetic acid as the solvent at room temperature. The influence of various reaction parameters such as solvent, concentration of solvent, oxidant amount, time, temperature, and catalyst amount was studied to optimize the reaction conditions. WMNLR calcined at 400 °C showed the highest catalytic activity towards oxidation of benzene with 12.7% conversion and 98% selectivity.Manganese nodule leached residue is an efficient catalyst for single-step benzene oxidation to phenol. H2O2 reacts with WMNLR to give hydroxyl radical through a redox mechanism, which attacks the benzene ring to give phenol. Among calcined samples WMNLR-400 shows the highest catalytic activity toward oxidation of benzene with 12.7% conversion and 98% selectivity.
Keywords: Manganese nodule leached residue; Surface characterization; Benzene; Oxidation; Phenol; Hydrogen peroxide
Metal patterning on silicon surface by site-selective electroless deposition through colloidal crystal templating
by Hidetaka Asoh; Seiji Sakamoto; Sachiko Ono (pp. 547-552).
Site-selective Cu deposition on a Si substrate was achieved by a combination of colloidal crystal templating, hydrophobic treatment, and electroless plating. Uniformly sized nano/microstructures were produced on the substrate using a monolayer coating of colloidal spheres instead of a conventional resist. The Cu patterns obtained were of two different types: networklike honeycomb and isolated-island patterns with a minimum period of 200 nm. Each ordered pattern with the desired intervals was composed of clusters of Cu nanoparticles with a size range of 50–100 nm. By the present method, it is possible to control the periodicity of metal arrays by changing the diameter of the colloidal spheres used as an initial mask and to adjust the shape of the metal patterns by changing the mask structure for electroless plating.
Keywords: Metal pattern; Electroless plating; Colloidal crystal templating; Hydrophobic treatment
The interaction of EDTA with barium sulfate
by Franca Jones; Phillip Jones; Mark I. Ogden; William R. Richmond; Andrew L. Rohl; Martin Saunders (pp. 553-561).
Ethylenediaminetetraacetic acid (EDTA) is a known complexing agent that interacts with a host of cations. In this paper, various techniques are used to elucidate the mechanism of interaction between EDTA and barium sulfate surfaces. It is shown that complexation with metal ions is not sufficient to explain the inhibition of barite crystallization but that other processes such as chemisorption must also occur. EDTA is shown to always adsorb as the mono-protonated species—suggesting that the molecule is able to lose a proton when it adsorbs at lower pH. Molecular modelling shows that the interaction of the surface barium ions with the carboxylate group is an important one. Finally, in situ turbidity measurements provide information about the mechanism of nucleation/growth modification. It is found that the EDTA molecule inhibits barium sulfate nucleation and that this could be its primary means of inhibiting precipitation of barium sulfate.Although the aminocarboxylate, ethylenediaminetetraacetic acid, is a known complexing agent, the mechanism by which it inhibits barium sulfate precipitation is better explained by adsorption onto critical nuclei.
Keywords: Barium sulfate; Molecular modelling; Precipitation; Infrared spectroscopy; Speciation; Adsorption; Inhibitors; Amino-carboxylates; Scale
Effects of sodium content and calcination temperature on the morphology, structure and photocatalytic activity of nanotubular titanates
by Chung-Kung Lee; Cheng-Cai Wang; Meng-Du Lyu; Lain-Chuen Juang; Shin-Shou Liu; Shui-Hung Hung (pp. 562-569).
Titanate nanotubes (TNT) were prepared via a hydrothermal treatment of TiO2 powders (P25) in a 10 M NaOH solution at 150 °C for 24 h and subsequently washed with HCl aqueous solution of different concentrations (0.1, 0.01, and 0.001 N). Samples with different contents of remnant sodium in nanotubes were characterized, as synthesized and after heat-treatment, by transmission electron microscopy, X-ray diffraction, and nitrogen adsorption–desorption isotherms. The photocatalytic activity of TNT was evaluated by photocatalytic oxidation of basic dye (basic violet 10 (BV10)) in water solution. It was found that if the sodium was not completely exchanged with proton, the removal of sodium increased the specific surface area (and pore volume), while the thermal stability was reduced. When the sodium content of TNT was approximately 0 wt% (nearly complete proton exchange), the nanotubular structure of titanates might be destroyed. The effects of the alterations of microstructures induced by the exchange of sodium and heat-treatment on the photocatalytic activity of TNT were discussed with the variations of specific surface area, pore volume, and the amounts of anatase phase in TNT.The photocatalytic activity of the TNT samples for BV10 is closely related to the sodium content and calcination temperature.
Keywords: Titanate nanotubes; Sodium; Calcination; Photocatalytic activity; Dye
Copper acetylacetonate anchored onto amine-functionalised clays
by Clara Pereira; Sónia Patrício; Ana Rosa Silva; Alexandre L. Magalhães; Ana Paula Carvalho; João Pires; Cristina Freire (pp. 570-579).
Copper (II) acetylacetonate was immobilised directly onto two clays, laponite (Lap) and K10-montmorillonite (K10), and after their amine functionalisation with (3-aminopropyl)triethoxysilane (APTES). All the materials were characterised by nitrogen adsorption isotherms at −196 °C, elemental analysis, TG-DSC, XRD, and IR spectroscopy. The K10-based materials were also characterised by XPS. The APTES-functionalised K10 showed higher copper loading than K10, indicating that the clay functionalisation enhanced the complex immobilisation; on the contrary, in Lap-based materials higher metal content was obtained by direct complex anchoring, probably due to the delaminated nature of Lap which induced the particles aggregation on functionalisation with APTES. All the results pointed out that the Cu complex was anchored onto the amine-functionalised clays by Schiff condensation between the amine groups of anchored APTES and the carbonyl groups of the acetylacetonate ligand, whereas direct immobilisation proceeded mostly through interaction between the metal centre and the clay surface hydroxyl groups.
Keywords: Copper (II) acetylacetonate; Laponite; Montmorillonite; Clay organofunctionalisation
Composite hybrid membrane of chitosan–silica in pervaporation separation of MeOH/DMC mixtures
by Jian Hua Chen; Qing Lin Liu; Jun Fang; Ai Mei Zhu; Qiu Gen Zhang (pp. 580-588).
Chitosan–silica hybrid membranes (CSHMs) were prepared by cross-linking chitosan (CS) with 3-aminopropyl-triethoxysilane (APTEOS). The dynamic behaviors of the CS membrane and the CSHM were investigated in pervaporation (PV) of methanol/dimethyl carbonate (MeOH/DMC) mixtures. The membranes were characterized by X-ray diffraction (XRD), contact angle meter, scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The transition state of PV processes were studied. During the PV processes, the amorphous region of the membranes increases and the contact angle between MeOH and the membrane decreases within a range of operating time and then remains almost constant implying a reconstruction occurred on the membrane surface. The silica is well distributed in the CSHM matrix and the thermal stability of the CSHM is enhanced. The time for a PV process to reach a steady state decreases with increasing MeOH concentration or feed temperature, and it is longer for the CSHM than the CS membrane under the same operating condition. Swelling experiments show that the degree of swelling (DS) is greatly depressed by cross-linking CS with APTEOS. Sorption data indicate that the selectivity of solubility and diffusion of the CSHM are greatly improved over the CS membrane. The CSHM presents superior separation behaviors over other membranes with a flux of1265g/(hm2) and separation factor of 30.1 in PV separation of 70 wt% MeOH in feed at 50 °C.Contact angle between MeOH and the CSHMs as a function of time immersed in MeOH/DMC mixtures with 30 wt% MeOH mass fraction at the temperature range of 30–50 °C.
Keywords: Chitosan; Hybrid membranes; Surface reconstruction; MeOH; Dimethyl carbonate
Dry grinding of Ca and octadecyltrimethylammonium montmorillonite
by Jana Hrachová; Jana Madejová; Peter Billik; Peter Komadel; Vladimír Štefan Fajnor (pp. 589-595).
Structural changes in Ca and octadecyltrimethylammonium (ODTMA) montmorillonite induced by dry grinding in a high-energy planetary ball mill were investigated by X-ray powder diffraction (XRD) analysis, infrared (IR) spectroscopy, and scanning electron microscopy (SEM). The organomontmorillonite is more resistant toward mechanical destruction than the Ca form. Both XRD and IR analyses indicate a complete breakdown of the mineral layers after 5 min of grinding of Ca-JP. The XRD pattern of the ODTMA clay shows disappearance of the layer ordering along the c axis after 40 min of grinding, while persistence of the layered structure for all tested samples is proven by the IR spectroscopy. The grinding process affects chemical bonds in the OH, SiOAl, and SiOSi groups of montmorillonite; however, no changes are observed for CH bonds of the organocations. In contrast to the Ca form, all absorption bands typical for montmorillonite appear in the IR spectrum of the ODTMA montmorillonite even after 40 min of grinding. The majority of the bands are undetectable in the spectrum of Ca montmorillonite ground for 5 min. Amorphization of the montmorillonite caused by an intense grinding process is markedly slower after replacing the inorganic cations with the long-chain alkylammonium cations.Amorphization of the montmorillonite caused by intense grinding process is markedly slower after replacing the inorganic cations with the long-chain octadecyltrimethylammonium cations.
Keywords: Mechanochemical treatment; Grinding; Amorphization; Montmorillonite; Organoclay; IR spectroscopy; XRD; SEM; EDX
Porous TiO2/SiO2 composite prepared using PEG as template direction reagent with assistance of supercritical CO2
by Jianxia Jiao; Qun Xu; Limin Li (pp. 596-603).
Titania–silica mesoporous composites have been prepared using polyethylene glycol (PEG) 20,000 as a template direction reagent with the assistance of supercritical carbon dioxide (SC CO2). For this preparation method, the composite precursors of tetrabutyl titanate (TBTT) and tetraethyl orthosilicate (TEOS) were dissolved in supercritical CO2 and impregnated into PEG 20,000 using SC CO2 as swelling agent and carrier. After removal of the PEG template by calcination in air at suitable temperatures, porous titania–silica composites were obtained. Effects of CO2 pressure and temperature have been studied on the impregnation ratio during the supercritical fluid condition. The composite products were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), FTIR spectroscopy, nitrogen sorption–desorption experiments, scanning electronic microscope (SEM), and transmission electron microscope (TEM). XRD and nitrogen sorption–desorption experimental results indicate that the titania–silica composite crystallized in anatase phase and has a preferable BET surface area up to 301.98 m2/g. It was also demonstrated that the microstructure and macroproperty of TiO2/SiO2 composites depend strongly on the experimental pressure during the impregnation process in SC CO2. At suitable CO2 pressure, silica even can be found in a single crystalline structure in nature by observation of TEM. At the same time, SEM indicates that the composite product existed in a spheric form or a cubic form inserted with many holes. So this work provides a new route to control and obtain the special micrography of TiO2/SiO2 composites with the aid of suitable polymer templates in supercritical CO2.
Keywords: TiO; 2; /SiO; 2; composite; PEG; Template; Supercritical CO; 2
Catalytic water dissociation using hyperbranched aliphatic polyester (Boltorn® series) as the interface of a bipolar membrane
by Yanhong Xue; Tongwen Xu; Rongqiang Fu; Yiyun Cheng; Weihua Yang (pp. 604-611).
The effect of hyperbranched aliphatic polyester (Boltorn® series) on the water dissociation in bipolar membranes was firstly investigated in this paper. The bipolar membranes were prepared by immersing the anion exchange layer in a hyperbranched aliphatic polyester solution and then coating on the layer a polyphenylene oxide (SPPO) solution. The SEM observations proved the existence of hyperbranched aliphatic polyester at the membrane intermediate layer. The adsorption amount was evaluated by the oxygen content via XPS. The junction thickness of the prepared bipolar membrane was determined by electrochemical impedance spectroscopy (EIS), and the membrane performances were evaluated by current–voltage curves. The results showed that the amount and generation of Boltorn® series, and temperature all affected I–V behaviors of the fabricated bipolar membranes, and the former two played the critical role. These effects were explained on the basis of the water dissociation theory and the characteristics of hyperbranched aliphatic polyester.Catalytic water dissociation using hyperbranched aliphatic polyester (Boltorn® series) as the interface of a bipolar membrane.
Keywords: Bipolar membrane; Catalytic water dissociation; Intermediate layer; Hyperbranched aliphatic polyester
SPEEK–zirconium hydrogen phosphate composite membranes with low methanol permeability prepared by electro-migration and in situ precipitation
by Bijay P. Tripathi; Vinod K. Shahi (pp. 612-621).
Sulfonated poly(ether ether ketone) (SPK)–zirconium hydrogen phosphate (ZrP) composite membranes were prepared by electro-driven migration of Zr4+ and simultaneous in situ precipitation of ZrP using phosphoric acid under different electrical gradient, in order to avoid loss in its mechanical stability. Degree of sulfonation was estimated from1H NMR and ion-exchange capacity study that was found to be 61% and 57%, respectively. In this method Zr4+ andHPO42− were allowed to diffuse within the pores/channels of the preformed SPK membrane under given electrical gradient and ZrP was precipitated within the membrane matrix. ZrP loading density was measured as a function of applied electrical gradient for a definite reaction time (4 h) and electrolytic environment. Membranes with varied ZrP loading densities were characterized for their thermal and mechanical stabilities, physicochemical and electrochemical properties using thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), scanning electron microscopy (SEM), water content, proton conductivity and methanol permeability. No loss in thermal and mechanical stability of membranes was observed due to incorporation of inorganic component (ZrP) in the membrane matrix. Although the composite membranes exhibited low proton conductivity in comparison to SPK membrane at room temperature, but the presence of the inorganic particles led to an improvement in high temperature conductivity. Selectivity parameter of these composite membranes was estimated at two temperatures namely 30 and 70 °C, in latter case it was found significantly higher than that for Nafion membrane (0.79×105 Sscm−3) under similar experimental conditions.Schematic diagram of a electrochemical method for preparing SPEEK–ZrP nanocomposite membrane.
Keywords: Proton-exchange membrane; Zirconium hydrogen phosphate; Composite membrane; Sulfonated poly(ether ether ketone); Membrane conductivity
Multi-color encoding of polystyrene microbeads with CdSe/ZnS quantum dots and its application in immunoassay
by Hai-Qiao Wang; Jian-Hao Wang; Yong-Qiang Li; Xiu-Qing Li; Tian-Cai Liu; Zhen-Li Huang; Yuan-Di Zhao (pp. 622-627).
Different diameter CdSe/ZnS semiconductor nanocrystals (average diameter: from ∼3.5 to ∼20 nm), quantum dots (QDs) were synthesized by changing the nucleation time, using organometallic reagents. These quantum dots possess narrow and symmetrical fluorescent emissions. The emission wavelengths of these composite dots span most of the visible spectrum from 500 through 700 nm. Furthermore, it is found that the quantum dots with an emission at ∼590 nm, tend to have a good quantum yield (such asΦ590=43.5%). While the emission wavelength of prepared CdSe/ZnS QDs shifts toward blue or red from 590 nm, the quantum yield tends to decrease. After that, optical encoding of microbeads with these quantum dots was carried out, and the spectra of encoded beads were identified. The result indicates that, to identify the encoded beads with different emission wavelengths and emission intensities, it is needed to acquire and differentiate the spectra of beads. After immobilized with human IgG, the encoded beads were used to detect the corresponding antibody in solution. The result indicates that the encoded beads can detect the antibody signal effectively. And the effective detection range of the antibody is about 2–15 μM.Multi-color encoding of microbeads with different quantum dots was carried out; the results indicate that, by using these encoded beads, the signal of the target molecule can be effectively identified.
Keywords: Quantum dots; Encoding of microbeads; Bead-based array technology; Immunoreaction
Preparation and characterization of highly mesoporous spherical activated carbons from divinylbenzene-derived polymer by ZnCl2 activation
by Zhaolian Zhu; Aimin Li; Lei Yan; Fuqiang Liu; Quanxing Zhang (pp. 628-634).
Highly mesoporous spherical activated carbons (SACs) were prepared from divinylbenzene-derived polymers by ZnCl2 activation; the effects of activation temperature and retention time on the yield and textural properties of the resulting SACs were studied. SACs thus prepared were characterized by N2 adsorption, X-ray diffraction (XRD), scanning electron microscopy (SEM), and aqueous adsorption assays. All the SACs were generated with high yield (>54%) and high mesopore fraction (around 80%). SEM and XRD analyses of SAC28 verified the presence of the disordered micrographite stacking with developed mesoporosity. Compared with conventional activated carbons, SAC28 prepared in our study exhibited a comparable adsorption capacity of 190 mg g−1 for bisphenol A and even more excellent capacity of 330 mg g−1 for phenol. Bisphenol A preloading significantly reduced the adsorption capacity of SAC28 for phenol due to both reduction of adsorption sites and pore blockage.
Keywords: Spherical activated carbon; Chemical activation; Characterization; Pore structure; Pore size distribution
Electric-field-enhanced transport in polyacrylamide hydrogel nanocomposites
by Reghan J. Hill (pp. 635-644).
Electroosmotic pumping through uncharged hydrogels can be achieved by embedding the polymer network with charged colloidal inclusions. Matos et al. [M.A. Matos, L.R. White, R.D. Tilton, J. Colloid Interface Sci. 300 (2006) 429–436], recently used the concept to enhance the diffusion-limited flux of uncharged molecules across polyacrylamide hydrogel membranes for the purpose of improving the performance of biosensors. This paper seeks to link their reported macroscale diagnostics to physicochemical characteristics of the composite microstructure. The experiments are characterized by a Debye screening length that is much larger than the radius of the silica nanoinclusions and the Brinkman screening length of the polymer skeleton. Accordingly, closed-form expressions for the incremental pore mobility are derived, and these are evaluated by comparison with numerically exact solutions of the full electrokinetic model. A mathematical model for the bulk electroosmotically enhanced tracer flux is proposed, which is combined with the electrokinetic model to ascertain the electroosmotic pumping velocity from measured flux enhancements. Because the experiments are performed with a known current density, but unknown bulk conductivity and electric field strength, theoretical estimates of the bulk electrical conductivity are adopted. These account for nanoparticle polarization, added counterions, and non-specific adsorption. Theoretical predictions of the flux enhancement, achieved without any fitting parameters, are within a factor of two of the experiments. Alternatively, if the Brinkman screening length of the polymer skeleton is treated as a fitting parameter, then the best-fit values are bounded by the range 0.9–1.6 nm, depending on the inclusion size and volume fraction. Independent pressure-driven flow experiments reported in the literature for polyacrylamide gels without inclusions suggest 0.4 or 0.8 nm. The comparison can be improved by allowing for hindered ion migration, while uncertainties regarding the inclusion surface charge are demonstrated to have a negligible influence on the electroosmotic flow. Finally, and perhaps most importantly, anomalous variations in the flux enhancement with particle size and volume fraction can be rationalized at present only by acknowledging that particle–particle and particle–polymer interactions increase the effective permeability of the hydrogel skeleton. This bears similarities to the increase in polymer free volume that accompanies the addition of silica nanoparticles to certain polymeric membranes.
Keywords: Hydrogel-composite membranes; Electrokinetic transport; Electroosmotic flow; Polyacrylamide gels; Incremental pore mobility; Brinkman screening length; Hydrodynamic permeability
Preparation of mesostructured barium sulfate with high surface area by dispersion method and its characterization
by Bhari Mallanna Nagaraja; Haznan Abimanyu; Kwang Deog Jung; Kye Sang Yoo (pp. 645-651).
The spherical and cubic mesoporous BaSO4 particles with high surface area were successfully produced via one-step process through precipitation reaction in aqueous solution of Ba(OH)2 and H2SO4 with ethylene glycol ( n-HOCH2CH2OH) as a modifying agent. The BaSO4 nanomaterial revealed that the high surface area and the mesoporous was stable up to 400 °C. Agglomerate mesoporous barium sulfate nanomaterials were obtained by the reaction of Ba2+ and SO2−4 with ethylene glycol aqueous solution. The ethylene glycol was used to control the BaSO4 particle size and to modify the surface property of the particles produced from the precipitation. The dried and calcined mesoporous BaSO4 nanomaterials were characterized by X-ray diffraction (XRD), BET surface area and N2 adsorption–desorption isotherm, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared resonance (FTIR) and thermogravimetric analysis (TGA). The as-prepared mesoporous dried BaSO4 possesses a high BET surface area of 91.56 m2 g−1, pore volume of 0.188 cm3 g−1 (P/P0=0.9849) and pore size of 8.22 nm. The SEM indicates that the morphology of BaSO4 nanomaterial shows shell like particles up to 400 °C, after that there is drastically change in the material due to agglomeration. Synthesis of mesoporous BaSO4 nanomaterial is of significant importance for both sulphuric acid decomposition and oxidation of methane to methanol.The mesoporous BaSO4 nanoparticles dispersed in ethylene glycol (EG) can be prepared by reacting H2SO4 with Ba(OH)2 in ethylene glycol and the resultant barium nano material have a regular ellipsoidal structure, with a shell wall thickness of 5–10 nm and an inner diameter of about 2–4 nm. The mesoporous BaSO4 nanomaterials prepared by using ethylene glycol have high surface area and their mesoporosity is stable up to 400 °C. The formation of the mesoporous structure is related both to nucleation and to the growth mechanism of the BaSO4 particles.
Keywords: Barium hydroxide; Sulphuric acid; Ethylene glycol; Mesoporous material
Density functional theory of adsorption in pillared slit-like pores
by Z. Sokołowska; S. Sokołowski (pp. 652-659).
We propose a density functional theory to describe adsorption of Lennard–Jones fluid in pillared slit like pores. Specifically, the pillars are built of chains that are bonded by their ends to the opposite pore walls. The approach we propose combines theory of quenched–annealed systems and theory of nonuniform fluids involving chain molecules. We compare the results of theoretical predictions with grand canonical ensemble Monte Carlo simulations and compute theoretical capillary condensation phase diagrams for several model systems.Pore filled with an adsorbate (violet spheres). Blue spheres are the segments of pillars.
Keywords: Adsorption; Pillared pore; Density functional theory; Monte Carlo simulation
Instability of confined thin liquid film trilayers
by Richard D. Lenz; Satish Kumar (pp. 660-670).
The instability of a system in which three stratified thin liquid films are confined in a channel with parallel walls and the interior film is subject to van der Waals-driven breakup is examined in this work. We derive a model based on lubrication theory and consisting of a pair of nonlinear partial differential equations describing the position of the two liquid interfaces. A linear stability analysis is carried out to show that the effects of varying the boundary film thicknesses can be understood in terms of several known limits, including a supported monolayer, confined bilayer, and supported bilayer. Variation of the boundary film viscosities is shown in many cases to eliminate the supported-bilayer limit. The parameter regimes in which squeezing and bending modes dominate the initial growth are determined, and nonlinear simulations are used to show that the mode always switches to squeezing near rupture. It is also found that a multi-modal dispersion relation may be created by asymmetries in thickness ratio, but not viscosity ratio, even in the absence of asymmetric interfacial tensions. The results of this study are expected to be relevant to multiphase microfluidic systems and the lithographic printing process.Instability of a system in which three stratified thin liquid films are confined in a channel and the interior film is subject to van der Waals-driven breakup is examined.
Keywords: Thin liquid films; Instability; Trilayers
Dewetting and surface properties of ultrathin films of cellulose esters
by P.M. Kosaka; Y. Kawano; D.F.S. Petri (pp. 671-677).
Surface properties of ultrathin films of cellulose esters deposited onto silicon wafers have been investigated by means of contact angle measurements and atomic force microscopy (AFM). Cellulose acetate (CA), cellulose acetate propionate (CAP), and cellulose acetate butyrate (CAB) films adsorbed or spin-coated onto Si wafers were annealed up to one week. Film stability was monitored by AFM. Dewetting has been observed for CA and CAP. Only CAB films with lower degree of esterification presented dewetting, CAB films with high degree of butyrate were stable even after one week annealing. Surface energy of CA, CAP, and CAB was indirectly determined by contact angle measurements using drops of water, formamide and diiodomethane. The surface energy decreased as the size of alkyl ester group or the degree of esterification increased because van der Waals interactions became weaker. Effective Hamaker constantAeff was calculated for CA, CAP, and CAB onto Si wafers in air. Negative values ofAeff were found for CA, CAP, and lower butyrate content CAB, which are related to instability and agree with dewetting phenomena observed by AFM. In contrast, a positiveAeff was determined for higher butyrate content CAB, corroborating with experimental observations.Surface energy of cellulose ester films deposited onto Si wafers decreased with the size of alkyl ester group. Dewetting of cellulose ester films was observed by AFM and explained with basis on the Hamaker constant values.
Keywords: Cellulose esters films; Hamaker constant; Surface energy
Adhesion between coating layers based on epoxy and silicone
by Jacob R. Svendsen; Georgios M. Kontogeorgis; Søren Kiil; Claus E. Weinell; Martin Grønlund (pp. 678-686).
The adhesion between a silicon tie-coat and epoxy primers, used in marine coating systems, has been studied in this work. Six epoxy coatings (with varying chain lengths of the epoxy resins), some of which have shown problems with adhesion to the tie-coat during service life, have been considered. The experimental investigation includes measurements of the surface tension of the tie-coat and the critical surface tensions of the epoxies, topographic investigation of the surfaces of cured epoxy coatings via atomic force microscopy (AFM), and pull-off tests for investigating the strength of adhesion to the silicon/epoxy systems. Calculations for determining the roughness factor of the six epoxy coatings (based on the AFM topographies) and the theoretical work of adhesion have been carried out. The coating surfaces are also characterized based on the van Oss–Good theory. Previous studies on the modulus of elasticity of the polymers involved have also been considered. It was found that adhesion problems might be due to inadequate wetting, the significantly different topographies, and differences in the mechanical strengths of the epoxies. Acid–base interactions calculated from the van Oss–Good theory were found useful in explaining the enhanced adhesion for some epoxy/silicon surfaces.Investigation of intercoat adhesion properties of a marine antifouling coating system. Figure shows transient development of surface tension of six different epoxy coatings.
Keywords: Paint; Surface tension; Antifouling; Surface topography; Adhesion strength
Static deflection measurements of cantilever arrays reveal polymer film expansion and contraction
by David Snow; Brandon L. Weeks; Dae Jung Kim; Albert Loui; Bradley R. Hart; Louisa J. Hope-Weeks (pp. 687-693).
An optical static method of detection is used to interpret surface stress induced bending related to cantilevers coated on one side with poly(vinyl alcohol), poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate), and poly(vinyl chloride-co-vinyl acetate-co-2-hydroxypropyl acrylate), or respectively, PVA, PVB, and PVC, and exposed to various solvent vapors. Results indicate that the adsorption and surface interactions of the different solvent vapors that cause polymer swelling and shrinking lead to rearrangements, which have been shown to change the elastic properties of the polymer film, and subsequently, the spring constant of the polymer coated cantilever. Static deflection measurements allow the direction of cantilever bending to be determined, which adds a new dimension of usefulness for surface functionalized cantilevers as transducers in the development of novel microelectromechanical systems (MEMS).An optical static method of detection is used to interpret surface stress induced bending related to cantilevers coated on one side with a polymer film, and exposed to various solvent vapors.
Keywords: MEMS; Cantilever; Spring constant; Surface stress; Polymer elasticity; Frenkel–Flory–Rehner
Condensation of a non-wetting fluid on a solid surface
by P. Neogi (pp. 694-698).
Theoretical studies of a drop moving under condensation from the surrounding vapor, have been provided. Two cases are considered. In the first, the rate of condensation is large that the drop “moves” because condensation has changed its dimensions. The model provided here shows that the rate of spreading is a constant, proportional to the heat flux and inversely proportional to the macroscopic contact angle. This compares well with available experimental data. The other model where the rate of condensation is small, is taken from existing results and comes close to explaining one set of experimental data. It is based on the use of viscous forces as the primary rate mechanism. Its shortcomings have been discussed.Movements due to condensation, large and small.
Keywords: Condensation; Thin liquid films; Spreading rate
Surfactant effects on thermocapillary interactions of deformable drops
by Michael A. Rother (pp. 699-711).
A three-dimensional boundary-integral algorithm is used to study thermocapillary interactions of two deformable drops in the presence of bulk-insoluble, non-ionic surfactant. The primary effect of deformation is to slow down the rate of film drainage between drops in close approach and prevent coalescence in the absence of van der Waals forces. Both linear and non-linear models are used to describe the relationship between interfacial tension and surfactant surface concentration. In the linear model, non-monotonic behavior of the minimum separation between the drops as a function of the surface Peclet numberPes is observed for equal drop and external medium viscosities and thermal conductivities. For bubbles with zero drop-to-medium viscosity and thermal conductivity ratios, however, the minimum separation increases withPes. There is a nearly linear relationship between the minimum drop separation and elasticity E. In the simplest non-linear equation of state, the product of the temperature and the surfactant concentration is retained by allowing non-zero values of the dimensionless gas constant Λ. ForΛ=O(0.05), it is possible for the smaller drop to move faster than the larger drop. In the Langmuir adsorption framework, the tendency of the smaller drop to catch up to the larger one decreases as the ratio of the equilibrium to maximum surfactant surface concentration increases. Finally, in the Frumkin model, a minimum in the drop separation occurs as a function of the interaction parameterλF for trajectories with all other parameters held constant.
Keywords: Surfactant; Thermocapillary; Drops; Bubbles
Interfacial properties of cetyltrimethylammonium-coated SiO2 nanoparticles in aqueous media as studied by using different indicator dyes
by E.Yu. Bryleva; N.A. Vodolazkaya; N.O. Mchedlov-Petrossyan; L.V. Samokhina; N.A. Matveevskaya; A.V. Tolmachev (pp. 712-722).
In this paper, we compare the properties of SiO2/water interface modified by cetyltrimethylammonium bromide (CTAB) with those of CTAB spherical micelles. The suspension of uniform silica nanoparticles coated with CTAB adlayer was investigated by using a set of acid–base indicators. The study of the colloidal system has been provided using electron microscopy and dynamic light scattering methods; the diameter of the initial SiO2 particles in dried state was ca. 40 nm. The increase in the ζ-potential value of nanoparticles from −34 to +(37–54) mV on going from pure silica suspension to the CTAB-containing system points on the silica surface recharging and formation of surfactant bilayer (or multilayer) on the silica/water interface. To obtain further information about the interfacial surfactant adlayer, the behavior of different indicator dyes has been studied in CTAB-modified SiO2 suspension. Comparison of the indices of apparent ionization constants, i.e.,pKaa values of phenol red, bromothymol blue, and fluorescein with those determined in CTAB micellar solutions have confirmed the supposition about certain similarity between CTAB-covered silica nanoparticles and common spherical surfactant micelles. However, the experiments on kinetics of bromophenol blue fading, as well as the spectral properties of methyl orange and solvatochromic Reichardt's indicator and some other data revealed the specificity of surfactant-coated silica nanoparticles, presumably, originating from their surface morphology.
Keywords: Cationic surfactants; Nanoparticles; Silica; Adlayer; Indicator dyes; Vis spectra; Protolytic equilibria
Glycerol-induced swollen lamellar phases with siloxane copolymers
by Aihua Zou; Heinz Hoffmann; Julian Eastoe; Otto Glatter (pp. 723-729).
Phase behavior is established for a block copolymer polyethyleneoxide– b–dimethylsiloxane–polyethylenoxide (EO)15–(PDMS)15–(EO)15 (IM-22) a in glycerol/water mixed solvent. In water alone, the block copolymer forms biphasic micellar/lamellar (L1/L α) systems over the range 10–70 wt%, with single L α-phases between 70–90 wt%. Strong solvent effects on the phase behavior were noted. For example, using a mixed 60:40 vol% glycerol/water solvent, the single L α-phase region appears at much lower concentrations, only 20 wt% IM-22, as compared to the biphasic L1/L α system observed in water alone. This interesting observation of L α-phase swelling on addition of glycerol may be explained by a decrease in attraction between the bilayers, as it is also found that in this mixed glycerol/water solvent there is a close refractive index matching with IM-22. Rheological measurements show the L α-phases with added glycerol have low shear moduli. The influence of added ionic surfactant sodium dodecylsulfate (SDS) on these swollen IM-22 L α-phases was studied. Small-angle X-ray scattering (SAXS) indicated the interlamellar distance d remains essentially constant up to 3 mM SDS, and then decreases with increasing SDS content. This weak effect is consistent with the fact that the L α-phases are most swollen when the mixed solvent contains 60 vol% glycerol. The results suggest that glycerol/water solvent mixtures can be used to tune the refractive index of the background solvent, modifying DLVO-type interactions, and causing significant effects on the phase stability of simple block-copolymer systems.Birefringence from 20 wt% siloxane copolymer in glycerol/water mixtures as a function of vol% glycerol in the solvent blend.
Keywords: L; α; -phases; Mixed solvents; SDS; Block copolymer; SAXS
Interaction of meso-tetrakis (4-sulfonatophenyl) porphyrin with cationic CTAC micelles investigated by small angle X-ray scattering (SAXS) and electron paramagnetic resonance (EPR)
by Patrícia S. Santiago; Diógenes de Sousa Neto; Leandro R.S. Barbosa; Rosangela Itri; Marcel Tabak (pp. 730-740).
Small angle X-ray scattering (SAXS) and electron paramagnetic resonance (EPR) have been used to investigate the interaction of the water-soluble meso-tetrakis (4-sulfonatophenyl) porphyrin (TPPS4) with cationic cethyltrimethylammonium chloride (CTAC) micelles. To evaluate if the porphyrin protonation state affects its interaction with the micelle, both SAXS and EPR measurements were performed at pH 4.0 and 9.0. The best-fit SAXS curves were obtained assuming for CTAC micelle a prolate ellipsoidal shape in the absence and upon incorporation of 2–10 mM TPPS4. SAXS results show that the presence of porphyrin impacts on micellar hydrophobic core, leading to a micellar reassembling into smaller micelles. Lineshapes of EPR spectra of 5- and 16-doxyl stearic acids (5- and 16-DSA, respectively) bound to 100 mM CTAC micelles exhibited slight changes as a function of porphyrin concentration. Spectral simulations revealed an increase of mobility restriction for both spin probes, especially at higher porphyrin concentration, where a small reduction of environment polarity was also observed for 16-DSA. The spin labels monitored only slight differences between pH 4.0 and 9.0, in agreement with the SAXS results.-size reduction (Rpar);-polar shell (σpol) is unchanged;-prolate ellipsoid shape remains;-TPPS4 location on the surface;-at highest TPPS4 concentration some intercalation in surface layer possible.
Keywords: Meso-tetrakis (4-sulfonatophenyl) porphyrin; Cationic cethyltrimethylammonium chloride; SAXS; EPR
Memory effects of monolayers and vesicles formed by the non-ionic surfactant, 2C18E12
by D.J. Barlow; C.M. Hollinshead; R.D. Harvey; L. Kudsiova; M.J. Lawrence (pp. 741-750).
The behaviour of monolayers and bilayers formed by the dialkyl chain non-ionic surfactant, 1,2-di- O-octadecyl- rac-glycerol-3- ω-methoxydodecaethylene glycol (2C18E12) in water at 297 K has been investigated. Using a surface film balance (or Langmuir trough) the compression–expansion cycle of the 2C18E12 monolayer was found to be reversible when compressed to surface pressures ( π) less than 42 mN m−1. Compression of 2C18E12 monolayer to π greater than 42 mN m−1 above this resulted in a considerable hysteresis upon expansion with the π remaining high relative to that obtained upon compression, suggesting a time/pressure dependent re-arrangement of 2C18E12 molecules in the film. Morphology of the 2C18E12 monolayer, investigated using Brewster angle microscopy, was also found to depend upon monolayer history. Bright, randomly dispersed domains of 2C18E12 of approximately 5 μm in size were observed during compression of the monolayer to π less than 42 mN m−1. At π of 42 mN m−1 and above, the surfactant film appeared to be almost completely ‘solid-like.’ Regardless of the extent of compression of the monolayer film, expansion of the film caused formation of chains or ‘necklaces’ of individual surfactant domains, with the extent of chain formation dependent upon pressure of compression of the monolayer and the length of time held at that pressure. Irreversible effects on 2C18E12 vesicle size were also seen upon temperature cycling the vesicles through their liquid–crystalline phase transition temperature with vesicles shrinking in size and not returning to their original size upon standing at 298 K for periods of more than 24 h. No comparable hysteresis, time, pressure or temperature effects were observed with the monolayer or vesicles formed by the corresponding phospholipid, disteaorylphosphatidylcholine, under identical conditions. The effects observed with 2C18E12 are attributed to the ability of the polyoxyethylene head group to dehydrate and intrude into the hydrophobic chain region of the mono- and bilayers. These studies have important implications for the use of the vesicles formed by 2C18E12 as drug delivery vehicles.The anomalous behaviour of monolayers and vesicles produced by a non-ionic dichain surfactant has been investigated using a combination of Langmuir trough, Brewster angle and variable temperature turbidity measurements.
Keywords: Non-ionic surfactant; Monolayers; Vesicles; Langmuir isotherm; Brewster angle microscopy; Variable temperature turbidity measurements
Dilution method study on the interfacial composition, thermodynamic properties and structural parameters of W/O microemulsions stabilized by 1-pentanol and surfactants in absence and presence of sodium chloride
by Bidyut K. Paul; Debdurlav Nandy (pp. 751-761).
The phase behaviors, interfacial composition, thermodynamic properties and structural characteristics of water-in-oil microemulsions under varied molar ratio of water to surfactant ( ω) at 303 K and also by varying temperatures at a fixedω(=40) by mixing with 1-pentanol and decane or dodecane in absence and presence of sodium chloride have been studied by the method of dilution. The surfactants used were cetyl pyridinium chloride (CPC), sodium dodecyl sulfate (SDS) and polyoxyethylene (23) lauryl ether (Brij-35). The compositions of 1-pentanol and the surfactant at the interfacial region, the distribution of 1-pentanol between the interfacial region and the continuous oil phase, and the effective packing parameter (Peff) at the threshold level of stability have been estimated. The thermodynamics of transfer of 1-pentanol from the continuous oil phase to the interface have been evaluated. The structural parameters viz. radii of the droplet (Re) and the waterpool (Rw), effective thickness of the interfacial layer (dI), average aggregation numbers of surfactants (N¯s) and the cosurfactant (1-pentanol) (N¯a) and the number of droplets (Nd) have also been estimated. The prospect of using these w/o microemulsions for the synthesis of nanoparticles with small size, have been discussed in the light of the radii of the droplet, and waterpool, the extent of variation of effective thickness of the droplet under varied molar ratio of water to surfactant and temperature. An attempt has been made to rationalize the results in a comprehensive manner.
Keywords: Dilution method; Water-in-oil microemulsions; Interfacial composition; Thermodynamic properties; Structural parameters
Structure and size of spontaneously formed aggregates in Aerosol OT/PEG mixtures: Effects of polymer size and composition
by M. Mercedes Velázquez; Margarita Valero; Francisco Ortega; J. Benito Rodríguez González (pp. 762-770).
Dynamic light scattering and Cryo-TEM measurements have allowed us to obtain the size and structure of spontaneous aggregates formed by mixtures of Aerosol OT, AOT, and ethylene glycol polymers of different molecular mass. The results presented in this work show that small unilamellar vesicles predominate in pure Aerosol OT solutions and in dilute polymer solutions mixed with AOT. In the latter case, elongated micelles coexist with unilamellar vesicles. When polymer concentration increases above a certain concentration, the small vesicles disappear and the size of the elongated micelles decreases to a radius compatible with spherical micelles. For PEG concentrations above the overlapping ones, spherical micelles coexist with very large aggregates probably formed by large rod like micelles or by superstructures of elongated micelles embedded in a polymer network. This behavior is consistent with theoretical models based in molecular mean-field theory [M. Rovira-Bru, D.H. Thompson, I. Szleifer, Biophys. J. 83 (2002) 2419]. The properties of the different types of aggregates are obtained by fluorescence spectroscopy and electrophoretic mobility measurements.Cryo-TEM micrographs from an aqueous solution of Aerosol OT 0.01 M.
Keywords: Aerosol OT; Spontaneous vesicles; Poly(ethylene glycol); Nabumetone; Fluorescence probing; Electrophoretic mobility; Light scattering measurements; Cryo-TEM
Synthesis and characterization of CdSe nanorods using a novel microemulsion method at moderate temperature
by L.F. Xi; Y.M. Lam (pp. 771-778).
CdSe nanoparticles have been successfully synthesized using a novel microemulsion method at moderate temperature. It is found that with a combination of the surfactant AOT and hydrazine hydrate, it is possible to control the morphology of the nanoparticles. The hydrazine hydrate acts as both a reducing agent and a templating agent that favors the formation of a rodlike structure. The composition, morphology and optical properties of the CdSe nanoparticles were investigated using powder X-ray diffraction (XRD), transmission electron microscopy (TEM), ultraviolet–visible (UV–vis) absorption spectroscopy, photoluminescence (PL) spectroscopy, energy dispersive X-ray spectroscopy (EDX) and Fourier transform infrared (FT-IR) spectroscopy. The nucleation and growth mechanism for this system is also proposed based on a time-dependent study. This synthesis route provides a moderate temperature (100 °C) method for synthesizing rodlike CdSe, hence reducing the possibility of oxidation of this chalcogenide compound.
Keywords: Colloidal method; Chalcogenide compound; Nanoparticles; Surfactant; Hydrazine hydrate
Factors affecting the stability of O/W emulsion in BSA solution: Stabilization by electrically neutral protein at high ionic strength
by Jongjit Rangsansarid; Kazuhiro Fukada (pp. 779-786).
Bovine serum albumin (BSA) was used as an emulsifier to disperse corn oil in aqueous media with various protein concentration, pH, and ionic strength. Quantitative estimation was made on the homogenizing activity of BSA and dispersion stability of oil particles by measuring particle size, turbidity, and creaming rate. Dispersion stability strongly depended on pH and became a minimum around pH 5.0 which was the isoelectric point of BSA. The interfacial tension between BSA solution and corn oil was minimized at pH 5.0. Interesting results were obtained concerning the ionic-strength dependence of stability. When the ionic strength was set below 30 mM, the emulsions became more stable with the increase of BSA concentration at pH 6.7 but the opposite behavior (enhanced destabilization) was confirmed at pH 5.0 with the BSA content. In high ionic strength conditions (ca. ⩾80 mM NaCl), however, BSA-stabilized emulsions became fairly stable even at pH 5.0. These results suggested that BSA molecules having no net charge induced some attractive interactions (e.g., bridging or depletion) in low ionic strength but steric stabilization in high ionic strength, respectively.
Keywords: Bovine serum albumin; Emulsifier; Interfacial tension; Particle size; Creaming rate; Isoelectric point; Ionic strength; Steric stabilization
Role of the solvophobic effect on micellization
by María Luisa Moyá; Amalia Rodríguez; María del Mar Graciani; Gaspar Fernández (pp. 787-795).
Experimental data of amphiphiles aggregation phenomena in water–organic solvent mixtures were considered with the idea of investigating the role of the solvophobic effect on micellization. Changes in the critical micelle concentration, in the micellar ionization degree (for ionic surfactants) and in the aggregation number accompanying variations in the composition of the bulk phase of the micellar solutions were examined with the scope of understanding which properties of the water–organic solvent mixtures are important in the micellization process. Results point out that the cohesive energy density, measured either through the Hildebrand–Hansen solubility parameter or the Gordon parameter, seems to play an important role in determining the contribution of the solvophobic effect on the Gibbs energy of micellization in water–organic solvents mixtures.
Keywords: Micellization; Solvophobic effect; Water–organic solvent mixtures; Polarity; Cohesive energy density; Solubility parameter
Stopped-flow kinetic studies of sphere-to-rod transitions of sodium alkyl sulfate micelles induced by hydrotropic salt
by Jingyan Zhang; Zhishen Ge; Xiaoze Jiang; P.A. Hassan; Shiyong Liu (pp. 796-802).
The kinetics and mechanism of sphere-to-rod transitions of sodium alkyl sulfate micelles induced by hydrotropic salt, p-toluidine hydrochloride (PTHC), were investigated by stopped-flow with light scattering detection. Spherical sodium dodecyl sulfate (SDS) micelles transform into short ellipsoidal shapes at low salt concentrations ([PTHC]/[SDS],χPTHC=0.3 and 0.4). Upon stopped-flow mixing aqueous solutions of spherical SDS micelles with PTHC, the scattered light intensity gradually increases with time. Single exponential fitting of the dynamic traces leads to characteristic relaxation time,τg, for the growth process from spherical to ellipsoidal micelles, and it increases with increasing SDS concentrations. This suggests that ellipsoidal micelles might be produced by successive insertion of unimers into spherical micelles, similar to the case of formation of spherical micelles as suggested by Aniansson–Wall (A–W) theory. AtχPTHC⩾0.5, rod-like micelles with much higher axial ratio form. The scattered light intensity exhibits an initially abrupt increase and then levels off. The dynamic curves can be well fitted with single exponential functions, and the obtainedτg decreases with increasing SDS concentration. Thus, the growth from spherical to rod-like micelles might proceed via fusion of spherical micelles, in agreement with mechanism proposed by Ikeda et al. AtχPTHC=0.3 and 0.6, the apparent activation energies obtained from temperature dependent kinetic studies for the micellar growth are 40.4 and 3.6 kJ/mol, respectively. The large differences between activation energies for the growth from spherical to ellipsoidal micelles at lowχPTHC and the sphere-to-rod transition at highχPTHC further indicate that they should follow different mechanisms. Moreover, the sphere-to-rod transition kinetics of sodium alkyl sulfate with varying hydrophobic chain lengths (n=10, 12, 14, and 16) are also studied. The longer the carbon chain lengths, the slower the sphere-to-rod transition.
Keywords: Sphere-to-rod transition; Rod-like micelles; Stopped-flow; Kinetics; Hydrotropic salt
Modulating properties of aqueous sodium dodecyl sulfate by adding hydrophobic ionic liquid
by Kamalakanta Behera; Siddharth Pandey (pp. 803-814).
Altering and modifying important physicochemical properties of aqueous surfactant solutions is highly desirable as far as potential applications of such systems are concerned. Changes in the properties of aqueous solutions of a common anionic surfactant sodium dodecyl sulfate (SDS) are assessed in the presence of a common and popular ‘hydrophobic’ ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (bmimPF6). Upon addition of up to∼0.10wt% bmimPF6, a dramatic decrease in critical micelle concentration (cmc) is accompanied by an increase in the degree of counterion dissociation ( α) and micellar aggregation number (Nagg) indicating micellar growth. However, in the range 0.10 wt% ⩽ bmimPF6 ⩽ 2.00 wt%, relatively gradual decrease in α andNagg is observed along with no change in cmc. Significantly decreased microfluidity of the aqueous SDS solutions on addition of bmimPF6 is indicated by a fluorescence microviscosity probe 1,3- bis-(1-pyrenyl)propane which suggests partitioning of bmimPF6 into the SDS micellar phase. Behavior of solvatochromic fluorescence probes, pyrene, pyrene-1-carboxaldehyde, and 2-( p-toluidino)naphthalene-6-sulfonate, confirms interaction, and possible complexation, between IL bmimPF6 and anionic micellar surface. Increased solubility of bmimPF6 with increasing SDS concentration further confirms SDS-bmimPF6 interactions. Presence of strong electrostatic attraction between bmim+ and anionic micellar surface is proposed to be the most dominant reason for these observations. All-in-all, unique role of a hydrophobic ionic liquid bmimPF6 in modifying the properties of aqueous anionic sodium dodecyl sulfate is demonstrated.Unique role of a hydrophobic ionic liquid toward modifying physicochemical properties of aqueous anionic sodium dodecyl sulfate is demonstrated.
Keywords: Anionic surfactants; Ionic liquids; Micelles; Fluorescence; Pyrene; cmc; Aggregation number
Small-angle X-ray scattering (SAXS) study on nonionic fluorinated micelles in aqueous system
by Lok Kumar Shrestha; Suraj Chandra Sharma; Takaaki Sato; Otto Glatter; Kenji Aramaki (pp. 815-824).
We have investigated the self-organization structures of perfluoroalkyl sulfonamide ethoxylate, C8F17SO2N(C3H7)(CH2CH2O)10H, a nonionic fluorinated surfactant in aqueous system by small-angle X-ray scattering (SAXS) technique. Structural modulation of the nonionic fluorinated micelle induced by temperature change, surfactant concentration, and the added fluorinated oils have been systematically studied. The SAXS data were analyzed by the indirect Fourier transformation (IFT), and the generalized indirect Fourier transformation (GIFT) depending on the volume fraction of the surfactant. Various plausible classical model calculations have been performed to confirm the consistency of the GIFT analysis of the SAXS data. Upon successive increase in temperature, the cylindrical micelles formed at lower temperatures undergo a continuous one-dimensional growth and ultimately near the cloud point an indication of flat planar like structural pattern is observed. The evolution in structure of particle near the demixing temperature may be due to onset of attractive interactions. The shape and size of the micelle is apparently unaffected by changing the surfactant concentration from 1 to 5 wt% at 25 °C. Nevertheless, addition of small amount of perfluoropolyether (PFPE) oil, of structure F(CF2CF2CF2O) nCF2CF2COOH (n∼21) modulate the micellar shape and size. Long cylindrical micelles eventually transform into globular like particles. The onset cylinder-to-sphere transition in the structure of micelles in the surfactant/water/oil system is probably due to amphiphilic nature of the oil, which tends to increase the spontaneous curvature. The lipophilic part of the oil tends to reside in the micellar core, whereas, the hydrophilic part goes close to the polar head group of the surfactant so that effective cross-sectional area per surfactant molecules increases and as a result spherical micelles tend to form. Perfluorodecalin (PFD) also decreases size of the micelles but its effect is poor compared to the PFPE oil.
Keywords: Fluorinated surfactant; Fluorinated oils; Small-angle X-ray scattering; Cylindrical micelles; Rheology; Oil solubilization
Effect of the structure of gelators on electro-optical properties of liquid crystal physical gels
by Jie He; Bin Yan; Binyu Yu; Ruiying Bao; Xiaoan Wang; Yinghan Wang (pp. 825-830).
Low molecular mass organic gelator (LMOG) as an important component of liquid crystal physical gel has a great influence on the electro-optical properties. In this paper, three analogues of amide gelator were synthesized and employed as LMOGs in nematic liquid crystal 5CB. Both hydrogen-bonding andπ–π-stacking interactions in the gel phase were found to stabilize the self-assembled structure. It was observed that the morphology was highly dependent on the crystallinity of gelators, which was affected by the intensity of hydrogen bonding. The thicker fibril was obtained with higher crystallinity of LMOG, while the thinner fibril was obtained with lower crystallinity. Moreover, the electro-optical properties of liquid crystal physical gels were proposed to be related to the interaction between the fibrils and the liquid crystal molecules.The influence of chemical structure of low molecular mass organic gelator (LMOG) on the electro-optical performance of liquid crystal physical gel was investigated. It is found that the morphology and electro-optical properties of liquid crystal physical gel were related to the crystallinity of LMOGs.
Keywords: Low molecular mass organic gelator; Liquid crystal physical gel; Electro-optical properties; Self-assembly
Electrophoretic separation of large DNAs using steric confinement
by Jérôme Mathé; Jean-Marc Di Meglio; Bernard Tinland (pp. 831-835).
We report an alternative method for electrophoretic separation of large DNAs using steric confinement between solid walls, without gel or obstacles. The change of electrophoretic mobility vs confinement thickness is investigated using fluorescence video microscopy. We observe separation at small confinement thicknesses followed by a transition to the bulk behavior (no separation) at a thickness of about 4 μm (a few radii of gyration for the studied DNA chains). We present tentative explanations of our original observations.
Keywords: Electrophoresis; Electroosmosis; DNA
Surface conductivity of colloidal particles: Experimental assessment of its contributions
by M.L. Jiménez; F.J. Arroyo; F. Carrique; A.V. Delgado (pp. 836-843).
In this work we investigate how combined data on dielectric dispersion and electrophoretic mobility of colloidal suspensions at different temperatures can be used to evaluate the two main quantities characterizing the solid/liquid interface, namely, the zeta potential and the stagnant layer conductivity (SLC). This is possible because the electric permittivity depends on the total surface conductivity, while the electrophoretic mobility is governed by both the zeta potential and that conductivity. Based on a simple analytical theory, we can also estimate the diffusion coefficient of counterions in the stagnant layer,DSL, for each temperature. The results lead to a good agreement between theory and experiment, although with somewhat high values ofDSL. With the aim of improving this description, we use a full theory of the electric permittivity of suspensions that accounts for the existence both of SLC and of a finite volume fraction of solids. An excellent description of the whole dielectric spectrum and of the electrophoretic mobility is possible in this case, although with still overestimated diffusion coefficients. This fact is discussed, and the importance of considering particle concentration effects even for suspensions that are often considered dilute is also stressed.Using a theory accounting for both finite volume fraction of solids and stagnant layer conductivity, it is possible to reproduce the whole experimental dielectric spectrum and the electrophoretic mobility of latex suspensions.
Keywords: Cell model; Dielectric dispersion; Polystyrene; Stagnant-layer conductivity; Surface conductivity; Zeta potential
Hydrodynamic forces acting on a microscopic emulsion drop growing at a capillary tip in relation to the process of membrane emulsification
by Krassimir D. Danov; Darina K. Danova; Peter A. Kralchevsky (pp. 844-857).
Here, we calculate the hydrodynamic ejection force acting on a microscopic emulsion drop, which is continuously growing at a capillary tip. This force could cause drop detachment in the processes of membrane and microchannel emulsification, and affect the size of the released drops. The micrometer-sized drops are not deformed by gravity and their formation happens at small Reynolds numbers despite the fact that the typical period of drop generation is of the order of 0.1 s. Under such conditions, the flow of the disperse phase through the capillary, as it inflates the droplet, engenders a hydrodynamic force, which has a predominantly viscous (rather than inertial) origin. The hydrodynamic boundary problem is solved numerically, by using appropriate curvilinear coordinates. The spatial distributions of the stream function and the velocity components are computed. The hydrodynamic force acting on the drop is expressed in terms of three universal functions of the ratio of the pore and drop radii. These functions are computed numerically. Interpolation formulas are obtained for their easier calculation. It turns out that the increase in the viscosity of each of the two liquid phases increases the total ejection force. The results could find applications for the interpretation and prediction of the effect of hydrodynamic factors on the drop size in membrane emulsification.The hydrodynamic force due to the liquid flux outgoing from a capillary favors the drop detachment in the process of membrane emulsification, and affects the size of the released drops.
Keywords: Membrane emulsification; Microchannel emulsification; Hydrodynamic forces; Drop formation at capillary tip
Nonlinear rheology of aqueous solutions of hydrophobically modified hydroxyethyl cellulose with nonionic surfactant
by G.Q. Guangqiang Zhao; Shing Bor Chen (pp. 858-866).
Shear thickening and strain hardening behavior of hydrophobically modified hydroxyethyl cellulose (HMHEC) aqueous solutions was experimentally examined. We focused on the effects of polymer concentration, temperature, and addition of nonionic surfactant. It is found that HMHEC shows stronger shear thickening at intermediate shear rates in a certain concentration range. In this range, the zero-shear viscosity scales with polymer concentration asη0∼c5.7, showing a stronger concentration dependence than for more concentrated solutions. The critical shear stress for complete disruption of the transient network followsτc∼c1.62 in the concentrated regime. Dynamic tests of the transient network on addition of surfactants show that the enhanced zero-shear viscosity is due to an increase in network junction strength, rather than their number, which in fact decreases. The reduction in the junction number could partly explain the weak variation of strain hardening extent for low surfactant concentrations, because of longer and looser bridging chain segments, and hence lesser nonlinear chain stretching.Normalized storage modulus versus strain in oscillatory shear for 0.4 wt% HMHEC with different concentrations of added C12E5 at 5 °C. The frequency is 1 Hz.
Keywords: Shear thickening; Strain hardening; Associative polymer; Nonionic surfactant; Rheology
Effect of friction between particles in the dynamic response of model magnetic structures
by Juan de Vicente; Javier Ramírez (pp. 867-876).
A simple particle-level simulation model that takes into account interparticle friction forces is developed to describe the dynamic response of magneto-rheological fluids. The results obtained for single-width particle chains are found to be in good agreement with slender body theory predictions [J. de Vicente, M.T. López-López, J.D.G. Durán, G. Bossis, J. Colloid Interface Sci. 282 (2005) 193]. The addition of side chains to a single-width one results in one order of magnitude increase of storage modulus and relaxation. The double logarithmic plot of storage and loss moduli vs frequency gives a limiting slope of one when including friction forces between particles. Simulation results are found to be in agreement with experimental measurements on an iron/kerosene model MR-fluid.Master curves corresponding to the dimensionless storage and loss moduli vs angular frequency for iron/kerosene MR-fluids in the viscoelastic linear region.
Keywords: Magnetorheology; Rheology; Viscoelasticity; Magnetic colloids; Spectral analysis; Simulation; Slender body
Exchange and reduction of Cu2+ ions in clinoptilolite
by I. Rodríguez Iznaga; V. Petranovskii; G. Rodríguez Fuentes; C. Mendoza; A. Benítez Aguilar (pp. 877-886).
The ion-exchange and reduction processes for Cu2+ ions in clinoptilolite from the Caimanes deposit (Moa, Cuba) were studied at different temperatures. The ion-exchange studies were done to determine the kinetic parameters of Cu2+ removal from solution by this clinoptilolite modified previously to NH+4 form, and thermodynamic parameters of Cu2+ elution from zeolite using NH4Cl solution. The results show that temperature increase favors the exchange and that it is a reversible process. The external diffusion rate appreciably increases with temperature, while, the internal diffusion coefficient rises relatively little. This means that besides ion exchange other processes (such as precipitation of the low-solubility phase and/or salt adsorption) occur, which cause copper removal from solution and affect the intracrystalline diffusion of the ions. For steric reasons the exchange of [Cu(H2O)6]2+ ions from a solution must occur with a number of water molecules n smaller than 6(6>n⩾0). Cu2+ reduction by hydrogen and the formation of Cu-particles in the clinoptilolite were verified. The Cu2+ reduction mechanism is complex, indirect, and sensitive to reduction temperature; consequently, Cu+ n states intermediate between Cu2+ and Cu0 should be present in the reduced samples.This article deals with Cu2+ ion exchange by natural clinoptilolite and consequent reduction of copper, leading to the formation of copper nanoparticles supported on a zeolite host.
Keywords: Natural zeolite; Clinoptilolite; Ion exchange; Thermodynamic and kinetic parameters; Copper; Reduction; Nanoparticles; UV–vis
Morphology-selective synthesis of polyhedral gold nanoparticles: What factors control the size and morphology of gold nanoparticles in a wet-chemical process
by Jong-Hee Lee; Kai Kamada; Naoya Enomoto; Junichi Hojo (pp. 887-892).
Polyhedral gold nanoparticles below 100 nm in size were fabricated by continuously delivered HAuCl4 and PVP starting solutions intol-ascorbic acid aqueous solution in the presence of gold seeds, and under addition of sodium hydroxide (NaOH). By continuously delivered PVP and HAuCl4 starting solutions in the presence of gold seed, the size and shape of polyhedral gold were achieved in relatively good uniformity (particle size distribution=65–95 nm). Morphological evolution was also attempted using different growth rates of crystal facets with increasing reaction temperature, and selective adsorption of PVP.The present study found that polyhedral gold nanoparticles with nanosizes below 100 nm can be synthesized by a wet-chemical route, carried out by the continuous addition of the HAuCl4 and PVP solutions intol-ascorbic acid aqueous solution at a relatively low temperature of 60 °C.
Keywords: Morphological control; Gold; Polyhedron; Polyvinylpyrrolidone; Nanostructure
Facile and controllable synthesis of polyoxometalate nanorods within polyelectrolyte matrix
by Yang Lan; Enbo Wang; Zhenhui Kang; Chunlei Wang; Baodong Mao; Chungui Tian; Lin Xu; Meiye Li (pp. 893-896).
Well dispersed polyoxometalate nanorods have been selectively and controllably synthesized within the polyelectrolyte (PE) films via a layer-by-layer (LbL) adsorption–precipitation method. The PE matrix was fabricated by LbL self-assembly technology and then the multilayer films containing polyoxometalate nanorods were constructed by repetitive adsorption of polyanions and subsequent precipitation with counter ions-tetraethylammonium bromide (TEAB). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) was used to observe the variation of size and morphology of the nanorods. The growth process and composition of the multilayer films containing nanorods were also studied.Well dispersed polyoxometalate nanorods have been synthesized controllably in the polyelectrolyte films via a layer-by-layer adsorption-precipitated method.
Keywords: Polyoxometalate; Nanorod; Layer-by-layer; Polyelectrolyte
Chemical analysis and aqueous solution properties of charged amphiphilic block copolymers PBA- b-PAA synthesized by MADIX®
by M. Jacquin; P. Muller; R. Talingting-Pabalan; H. Cottet; J.F. Berret; T. Futterer; O. Théodoly (pp. 897-911).
We have linked the structural and dynamic properties in aqueous solution of amphiphilic charged diblock copolymers poly(butyl acrylate)- b-poly(acrylic acid), PBA- b-PAA, synthesized by controlled radical polymerization, with the physico-chemical characteristics of the samples. Despite product imperfections, the samples self-assemble in melt and aqueous solutions as predicted by monodisperse microphase separation theory. However, the PBA core are abnormally large; the swelling of PBA cores is not due to AA (the Flory parameterχPBA/PAA, determined at 0.25, means strong segregation), but to h-PBA homopolymers (content determined by liquid chromatography at the point of exclusion and adsorption transition, LC-PEAT). Beside the dominant population of micelles detected by scattering experiments, capillary electrophoresis CE analysis permitted detection of two other populations, one of h-PAA, and the other of free PBA- b-PAA chains, that have very short PBA blocks and never self-assemble. Despite the presence of these free unimers, the self-assembly in solution was found out of equilibrium: the aggregation state is history dependant and no unimer exchange between micelles occurs over months (time-evolution SANS). The high PBA/water interfacial tension, measured at 20 mN/m, prohibits unimer exchange between micelles. PBA- b-PAA solution systems are neither at thermal equilibrium nor completely frozen systems: internal fractionation of individual aggregates can occur.The self-assembly of amphiphilic diblocks in water (large core size of micelles, low CMC but presence of free unimers, hysteretic fractionation) are explained via a precise physico/chemical analysis of samples.
Keywords: Diblock copolymer; Micelle; Interfacial tension; Exchange kinetics; Self-assembly; Polyelectrolyte; Fractionation
Monolayer behavior of a pyridyl head-group-containing amphiphile and its miscibility with poly(d,l-lactide-co-glycolide) on different pH subphase
by Miao Xu; Lu Sun; Shengyan Yin; Chunli Liu; Lixin Wu (pp. 912-920).
In this paper, we investigated the Langmuir film and Langmuir–Blodgett (LB) monolayer film of a nonionic amphiphilic molecule, 4-(6- p-pyridyloxyl)hexyloxyl-4′-dodecyloxylazobenzene (C12AzoC6Py) and its mixture with poly(d,l-lactide-co-glycolide) (PLG) at different subphase pH values (2.0, 2.6, 3.3, 4.4, and 6.5, respectively) by surface pressure–area (π–A) isotherms, in situ interface Brewster angle microscopy (BAM), and ex situ atomic force microscopy (AFM). For pure C12AzoC6Py, itsπ–A isotherms display a plateau when the subphase pH value is lower than 3.0. The pressure of the plateau increases with the decrease of pH until 2.0. Over the plateau, theπ–A isotherms become almost identical to the one under neutral conditions. The appearance of such a plateau can be explained as the coexistence of protonation and unprotonation of pyridyl head groups of the employed amphiphile. In contrast to the homogeneous surface morphology of pure C12AzoC6Py near the plateau by BAM observation, the surface in the case of its mixing with PLG exhibits a dendritic crystalline state under low surface pressure at subphase pH lower than 3.0. The crystalline state becomes soft and gradually melts into homogeneous aggregates with surface pressure increasing to a higher value than that of the plateau. Meanwhile, the hydrolysis of PLG in the mixture system at the interface has been affirmed to be restrained to a very large extent. And the PLG was believed to be compelled to the up layer of the LB film due to the phase separation, which is examined by AFM. Based on the experimental results, the corresponding discussion was also performed.Phase behavior of a pyridyl head-group-containing amphiphile and its mixture with poly(d,l-lactide-co-glycolide) at air/water interface is studied by adjusting subphase pH, and interesting dendritic crystalline state and phase separation are examined.
Keywords: Pyridyl-head group-amphiphile; PLG; Interface aggregation; Miscibility
3D flower-like Y2O3:Eu3+ nanostructures: Template-free synthesis and its luminescence properties
by Suyuan Zeng; Kaibin Tang; Tanwei Li; Zhenhua Liang (pp. 921-929).
In this work, a facile route using simple hydrothermal reaction and sequential calcinations to synthesize 3-dimensional flower-like Y2O3:Eu3+ nanoarchitectures without employing templates or matrix for self-assembly is presented. The flower-like nanostructures are composed of nanosheets with thickness of about 30 nm, which is verified by the field-emission electron microscopy (FESEM). Influencing factors such as the dosage of reactants, the solvent, and pH are systematically investigated. The time-dependent experiments indicate a self-assembly mechanism. This method is also applicable in the preparation of other lanthanide oxides. The PL spectra of the as-synthesized Y2O3:Eu3+ are systematically studied. Both the Eu3+ concentration and the calcinations temperature have great effect on the luminescence intensity of5D0–7F2 transition. The decay curve of the5D0 transition shows that the lifetime of the as-obtained Y2O3:Eu3+ is about 2.4 ms.The sample is composed of a large number of uniform flower-like nanostructures. The average size of the as-obtained nanostructure is about 6 μm. A closer inspection further reveals that the flower is made up of many thin petals, the thickness of which is ca. 30 nm.
Keywords: Y; 2; O; 3; :Eu; 3+; Hydrothermal; Flower-like; 3-Dimensional nanostructure; Luminescence
Use of the ternary phase diagram of a mixed cationic/glucopyranoside surfactant system to predict mesostructured silica synthesis
by Rong Xing; Stephen E. Rankin (pp. 930-938).
Mixed surfactant systems have the potential to impart controlled combinations of functionality and pore structure to mesoporous metal oxides. Here, we combine a functional glucopyranoside surfactant with a cationic surfactant that readily forms liquid crystalline mesophases. The phase diagram for the ternary system CTAB/H2O/ n-octyl- β-d-glucopyranoside (C8G1) at 50 °C is measured using polarized optical microscopy. At this temperature, the binary C8G1/H2O system forms disordered micellar solutions up to 72 wt% C8G1, and there is no hexagonal phase. With the addition of CTAB, we identify a large area of hexagonal phase, as well as cubic, lamellar and solid surfactant phases. The ternary phase diagram is used to predict the synthesis of thick mesoporous silica films via a direct liquid crystal templating technique. By changing the relative concentration of mixed surfactants as well as inorganic precursor species, surfactant/silica mesostructured thick films can be synthesized with variable glucopyranoside content, and with 2D hexagonal, cubic and lamellar structures. The domains over which different mesophases are prepared correspond well with those of the ternary phase diagram if the hydrophilic inorganic species is assumed to act as an equivalent volume of water.
Keywords: Lyotropic; Liquid crystal; Templating; Mixed surfactants; Nanocasting; Polycondensation
Synthesis of ligand-selective ZnS nanocrystals exhibiting ligand-tunable fluorescence
by M. Habib Ullah; Bonghwan Chon; Taiha Joo; Minsoo Son; Il Kim; Chang-Sik Ha (pp. 939-946).
High-quality ZnS nanocrystals (NCs) of nearly identical size are synthesized using isomeric ligands, o-, m-, p-phenylenediamines (PDAs) that bind to the NC cores. The fluorescence emission from the NC is tunable according to the structure of the isomer. The measured fluorescence quantum yields (QYs) are 2–3 times higher for NCs that are passivated with isomeric PDA ligands than the fluorescence QY of NCs prepared at the absence of PDAs. The NC morphologies were studied by low-angle and wide-angle X-ray diffraction (XRD), and by transmission electron microscopy (TEM). The average correlating sizes were found to be3.0±0.3,3.7±0.30, and3.0±0.5nm for the NCs that were passivated with o-PDA, m-PDA, and p-PDA, respectively. The Fourier-transform infra-red (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) studies were carried out to investigate the shell structure and the interaction between the core and the shell. The adsorbed ligands were quantitatively analyzed by TGA. The structure, morphology, and optical properties of these PDA passivated NCs were compared with the NCs prepared in the absence of PDA.High-quality ZnS nanocrystals (NCs) of nearly identical size are readily synthesized using isomeric ligands allowing defectless fluorescence emissions that are tunable according to the nature of the ligand.
Keywords: Isomeric ligands; Phenylenediamine; ZnS nanocrystals; Fluorescence tuning
Thermal annealing of Au nanorod self-assembled nanostructured materials: Morphology and optical properties
by Xiaoge Hu; Tie Wang; Shaojun Dong (pp. 947-953).
Three-dimensional Au nanorod and Au nanoparticle nanostructured materials were prepared by layer-by-layer self-assembly. The plasmonic properties of the Au nanorod and Au nanoparticle self-assembled nanostructured materials (abbreviated as AuNR and AuNP SANMs) are tunable by the controlled self-assembly process. The effect of thermal annealing at 180 and 500 °C to the morphologies, plasmonic properties and surface-enhanced Raman scattering (SERS) responses of these SANMs were investigated. According to the experimental results, these properties correlate with the structure of the SANMs.
Keywords: Nanorod; Nanoparticle; Thermal anneal; Self-assembly
Structural and morphological transformations of mesostructured titanium phosphate through hydrothermal treatment
by Lianzhou Wang; Zhimin Yan; Shizhang Qiao; G.Q. Max Lu; Yining Huang (pp. 954-961).
The phase transformation of mesostructured titanium phosphate (TiPO) from hexagonal to lamellar structure was observed in a simply hydrothermal treatment, accompanied by drastically morphological changes in the micrometer-sized particles. XRD pattern revealed that different mesostructures were obtained by simply varying hydrothermal temperature or treatment duration. SEM and TEM observations showed the morphological evolution from individual particles to interconnected nanoplatelets. A significant blue shift in UV–vis spectra was observed for lamellar mesostructured material, which may be associated with the different coordinated Ti-sites in the hexagonal and lamellar mesostructures. FT-IR spectra and detailed31P MAS NMR studies indicated that additional POH groups were presented in the lamellar structure, which might play a key role in the structural and morphological transformations of mesostructures.The hexagonal to lamellar phase transformation and drastically morphological change of mesostructured titanium phosphate were achieved by a simply hydrothermal treatment.
Keywords: Mesostructure; Titanium phosphate; Phase transformation; Hydrothermal treatment
A water-soluble polythiophene–Au nanoparticle composite for pH sensing
by Biswa Ranjan Panda; Arun Chattopadhyay (pp. 962-967).
In this paper, we report the development of a reversible pH sensor in aqueous medium based on the fluorescence properties of a polythiophene–gold nanoparticle (Au NP) composite. The composite was synthesized in water by simultaneous reduction of HAuCl4 to Au NPs and polymerization of thiophene in the presence of no additional reagents. It was stable for weeks and had characteristic emissions, which changed in the pH range of 3.0 to 6.0, thus providing a mean for probing the pH of an aqueous solution. Measurement of the pH could be performed over several cycles of titrations, pointing to the robustness of the materials for such sensing applications. The mass spectra of the composite at two extreme pH values were identical, indicating that the primary structure of the polymer was not affected due to changes in pH of the medium. Transmission electron microscopic (TEM) measurements indicated the presence of small sized Au NPs with the polymer in the milieu. The composite could be titrated by acid (or base) and considering the acid–base equilibria at different pHs, we have been able to calculate the pKeq of the composite, which was further used in calculating the pH of an aqueous solution from the emission spectrum of the composite. Our approach took advantage of redox chemistry in synthesizing the water-soluble composite and the optical behavior of a conjugated polymer in developing an important pH sensor, which may form the basis of further development of versatile pH or other sensors by suitably modifying the backbone of the monomer.A new water-soluble fluorescent composite of polythiophene and Au nanoparticles exhibits pH-dependent fluorescence, which has been used to quantitatively detect the pH of a medium in the range of 3.00 to 6.00.
Keywords: Polymer; Nanoparticles; pH; Sensor; Fluorescence; Composite
Investigation of inorganic cluster–surfactant flocculants for virion sequestration and removal from aqueous media
by May Nyman; Jill M. Bieker; Steven G. Thoma; Daniel E. Trudell (pp. 968-976).
Anionic polyoxometalates or cationic aluminum clusters when combined with a surfactant of an opposite charge form hydrophobic precipitates that are approximately lamellar with alternating layers of interdigitated surfactant tails and inorganic clusters. The charged surfactant heads are associated with the inorganic cluster layers. When these phases self-assemble and precipitate from aqueous media spiked with a virus titer, either bovine enterovirus (BEV) or influenza A, the precipitates effectively sequester the virions via an enmeshment process. These studies were done via precipitation and filtration of the cluster–surfactant floc in the presence of the virus, followed by reverse transcriptase polymerase chain reaction ( rRT-PCR) analysis of the filtrate. Efficacy of these cluster–surfactant phases for virion sequestration is variable as a function of their solubility, the size of colloid formed in solution, and their degree of long-range order. Generally less soluble, poorly ordered precipitates that form the largest colloids are the most effective virion sequestering media. Cluster–surfactant phases were characterized in solution by nuclear magnetic resonance (NMR) and dynamic light scattering (DLS); and in the solid-state by powder X-ray diffraction and solid-state magic angle spinning (MAS) NMR.Hydrophobic inorganic cluster–surfactant phases are highly effective for removing virions from aqueous media.
Keywords: Polyoxometalate; Surfactant-enclosed clusters (SECs); Aluminum tridecamer; Virion sequestration; Reverse transcriptase polymerase chain reaction (; r; RT-PCR); Water treatment; Flocculants; Dynamic light scattering (DLS)
Reversible aggregation of gold nanoparticles induced by pH dependent conformational transitions of a self-assembled polypeptide
by Jeung-Yeop Shim; Vinay K. Gupta (pp. 977-983).
Controlling the stable structures of metallic nanoparticles on mesoscopic and macroscopic length scales is of great interest in nanotechnology. Here, this task is accomplished using a synthetic biopolymer that is responsive to external stimuli and undergoes changes in secondary structure. Reversible aggregation of gold nanoparticles (GNP) is induced by pH dependent changes in a self-assembled monolayer of disulfide modified poly(l-glutamic acid) (SSPLGA) withMw∼27000. The disulfide anchoring group drives chemisorption onto the gold nanoparticles and leads to the formation of a self-assembled monolayer. Characterization of the modified GNP and its aggregation behavior is performed using dynamic light scattering (DLS), UV–vis and IR spectroscopy, and transmission electron microscopy (TEM). Experimental results show that decrease in pH near 5.5 leads to aggregation of the modified GNP. The change in aggregation behavior with pH occurs within minutes, is reversible, and happens within a narrow range of pH from about 4.5 to 5.5. Comparison with literature data on molar enthalpy of hydrogen bonding, specific optical rotation, and ionization for the helix–coil transition of PLGA indicates that the aggregation of the SSPLGA modified GNP corresponds to the transition in the secondary structure of the polyacid.Reversible change in aggregation of gold nanoparticles with a self-assembled layer of PLGA polypeptide that undergoes helix–coil transition with pH.
Keywords: Gold nanoparticles; Reversible aggregation; Self-assembly; Self-assembled polypeptide
A new approach to the phenomena at the interfaces of finely dispersed systems
by Aleksandar M. Spasic; Mihailo P. Lazarevic (pp. 984-995).
A new idea has been applied for the elucidation of the electron and momentum transfer phenomena, at both rigid and deformable interfaces, in finely (micro-, nano-, atto-) dispersed systems. The electroviscoelastic behavior of, e.g., liquid/liquid interfaces (emulsions and double emulsions), is based on three forms of “instabilities”; these are rigid, elastic, and plastic. The events are understood as interactions between the internal (immanent) and external (incident) periodical physical fields. Since the events at the interfaces of finely dispersed systems must be considered at the molecular, atomic, and/or entities level it is inevitable to introduce the electron transfer phenomenon beside the classical heat, mass, and momentum transfer phenomena commonly used in chemical engineering. Therefore, an entity can be defined as the smallest indivisible element of matter that is related to the particular transfer phenomena. Hence, the entity can be either differential element of mass/demon, ion, phonon as quanta of acoustic energy, infon as quanta of information, photon, and electron. Three possible mathematical formalisms have been derived and discussed related to this physical formalism, i.e., to the developed theory of electroviscoelasticity. The first is the stretching tensor model, where the normal and tangential forces are considered, only in mathematical formalism, regardless of their origin (mechanical and/or electrical). The second is the classical integer-order van der Pol derivative model. Finally, the third model comprises an effort to generalize the previous van der Pol differential equations, both linear and nonlinear, where the ordinary time derivatives and integrals are replaced by corresponding fractional-order time derivatives and integrals of orderp<2 (p=n−δ,n=1,2,δ≪1). In order to justify and corroborate a more general approach the obtained calculated results were compared to those experimentally measured using the representative liquid/liquid system.
Keywords: Electroviscoelasticity; Electron transfer phenomena; Electrified liquid/liquid interfaces; Fractional-order model; Finely dispersed systems; Numerical evaluation; Predictor–corrector method; Asymptotic expansion; Emulsions; Double emulsions
Effects of a static magnetic field on water and electrolyte solutions
by Lucyna Holysz; Aleksandra Szczes; Emil Chibowski (pp. 996-1002).
Water and electrolyte solutions were exposed for 5 min to a weak static magnetic field (B=15mT). Their conductivity and the amount of evaporated water were then measured as a function of time. Simultaneously, these quantities were determined for magnetically untreated samples, as reference systems. It was found that a magnetic field influences these two parameters and their changes depend on the thermodynamic functions of hydration of these ions. A roughly linear change in conductivity versus ‘scaled’ functions was obtained. On this basis it was concluded that the magnetic field causes changes in the hydration shells of the ions.
Keywords: Magnetic field; Water; Electrolyte solutions; Conductivity; Evaporation
Thermodynamic assessment of the variation of the surface areas of two synthetic swelling clays during adsorption of water
by S. Lantenois; Y. Nedellec; B. Prélot; J. Zajac; F. Muller; J.-M. Douillard (pp. 1003-1011).
Two synthetic smectites (montmorillonite and beidellite) are studied by a water adsorption technique in order to assess their specific surface areas under atmospheric conditions. A route recently proposed for extracting the thermodynamic data from experimental adsorption isotherms is used. The variation of the specific surface area during water adsorption is obtained, which can be linked to the enlargement of the interlayer space determined using X-ray diffraction. This variation is compared to an idealized specific surface area obtained from TEM and X-ray measurements in agreement with crystallographic models. All these results are also compared with those obtained previously for a natural montmorillonite. A simple view of swelling is proposed.
Keywords: Montmorillonite; Beidellite; Synthetic smectite; Water; Adsorption; Surface area; Swelling clay; Interlayer space
Dynamics of condensation of wetting layer in time-dependent Ginzburg–Landau model
by Masao Iwamatsu (pp. 1012-1016).
The dynamics of liquid condensation on a substrate or within a capillary is studied when the wetting film grows via interface-limited growth. We use a phenomenological time-dependent Ginzburg–Landau (TDGL)-type model with long-range substrate potential. Using an order parameter, which does not directly represent the density, we can derive an analytic formula for the interfacial growth velocity that is directly related to the substrate potential. Using this analytic expression the growth of wetting film is shown to conform to a power-law-type growth, which is due to the presence of a long-range dispersion force.Growing liquid film with a planar wave front as the envelop of spherical wave fronts.
Keywords: Condensation; Wetting; Dynamics
Thermodynamics of mechanical transduction of surface confined receptor/ligand reactions
by Paolo Bergese; Giulio Oliviero; Ivano Alessandri; Laura E. Depero (pp. 1017-1022).
Chemomechanics of surface stress is discussed in terms of interfacial thermodynamics. In the first section the paper shows how to quantitatively describe the chemical equilibrium of a receptor/ligand binding reaction confined at a solid–liquid interface and how the overall work of the reaction splits into chemical and surface work, that appears as a surface pressure. In the second section this thermodynamic model is applied to describe the experimental results of microcantilever bending induced by DNA hybridization occurring onto one of its faces.The overall work of a receptor/ligand binding reaction confined at a solid–liquid interface splits into chemical and surface work, that appears as a surface pressure. If the surface is one of the faces of a microcantilever, the microcantilever balances the pressure by bending.
Keywords: Thermodynamics; Interfaces; Chemomecanical transduction; Microcantilevers
Degree of counterion binding on water in oil microemulsions
by E. Fernández; L. García-Río; P. Rodríguez-Dafonte (pp. 1023-1026).
An ion-exchange process has been used to prepare HOT from NaOT (sodium bis(2-ethylhexyl)sulfosuccinate), where the Na+ counterion has been replaced by H+. The acidity function,H0, of the aqueous core of HOT-based microemulsions decreases with W fromH0≈0.6 atW>20 toH0=−1.4 atW=2. On the basis of theH0 acidity function of the aqueous core and the dependence ofH0 on acid concentration, we have been able to determine the degree of counterion binding ( β) in microemulsions with a value ofβ≈0.92 which is practically independent of the water content of the system.We have determined the degree of counterion binding ( β) in water-in-oil microemulsions with a value ofβ≈0.93 which is practically independent of the water content of the system.
Keywords: Microemulsion; Acidity function; Neutralized charge; Counterion binding
Photo-isomerization of spiropyran-modified cationic surfactants
by Hideki Sakai; Hiroatsu Ebana; Kenichi Sakai; Koji Tsuchiya; Takahiro Ohkubo; Masahiko Abe (pp. 1027-1030).
Photo-induced isomerization of a newly synthesized surfactant, 1′(6-trimethylammoniododecyl)-3′,3′-dimethyl-6-nitrospiro-(2H-1-benzopyran-2,2′-indoline) bromide (SP-Me-12), has been characterized on the basis of the UV–vis absorption spectra and the surface tension data. Visible light (λ>420nm) incident on the aqueous solution of SP-Me-12 results in the isomerization from the merocyanine (MC) form to the spiropyran (SP) form; this structural change was confirmed by a complete disappearance of a characteristic absorption peak of the MC form. When the surfactant solution is stored in the dark, the isomerized SP form reverts to the original MC form, however, the reverse isomerization rate is observed to be considerably slower than that seen for visible light irradiation (from the MC form to the SP form). A reversible change in the surface tension of the aqueous surfactant solution is observed for the photo-induced isomerization: the surface tension measured below the critical aggregation concentration decreases as a result of the visible light irradiation and it is gradually reversed to the original level during the equilibration in the dark.The photo-induced isomerization of a spiropyran-modified cationic surfactant has been characterized with a combination of the UV–vis absorption spectroscopy and surface tensiometry.
Keywords: Spyropyran; Surfactant; Photo-isomerization; Surface tension