Journal of Colloid And Interface Science (v.337, #2)
Understanding the role of each ingredient in a basic copper carbonate based impregnation recipe for respirator carbons
by J.W.H. Smith; P. Westreich; L.M. Croll; J.H. Reynolds; J.R. Dahn (pp. 313-321).
Scanning Electron Microscope image of the inner surface of an impregnated activated carbon sample.Basic copper carbonate (Cu2CO3(OH)2) is often used as an impregnant in activated carbons for respiratory filters. The mechanisms that allow adsorption of toxic gases by an activated carbon loaded with a Cu2CO3(OH)2-based impregnation recipe are studied here. Several samples were studied to determine the effect of ingredients added during impregnation, impregnant loading and drying temperature on performance. The filtering capacity of the samples is quantified by the stoichiometric ratio of reaction (SRR) between the impregnant and the challenge gas. X-ray diffraction (XRD), thermal gravimetric analysis (TGA), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX) were used to characterize the impregnant both on and off the carbon as a function of loading and heat-treatment temperature. The influence of the phase and dispersion of the impregnant on the SRR is the focus of this report.
Keywords: Impregnated activated carbon; Impregnant; Thermal evolution; Impregnant distribution; Impregnant grain size; Impregnant phase; Stoichiometric ratio of reaction; Gas filtration capacity
A spectroscopic investigation into the interaction between bile salts and insulin in alkaline aqueous solution
by Zhang Yong; Deng Yingjie; Lu Ming; Duncan Q.M. Craig; Li Zhengqiang (pp. 322-331).
Schematic diagram describing the bile salt binding to insulin and the bile salt-mediated dissociation of insulin oligomers (all cases are not stoichiometrically quantifiable in the volume and number of molecules).The interaction of a bile salt, sodium deoxycholate, with insulin was investigated by ultraviolet derivative spectroscopy, fluorescence, circular dichroism and photon correlation spectroscopy. The results indicate that the conversion of insulin from a monomer to a dimer, tetramer, or hexamer occurs over a concentration range of5.5×10-2–1.1×10-1mg/ml in alkaline solution in the absence of bile salts, and that insulin exists primarily as a hexamer complex above this concentration. Evidence is presented that bile salt-induced dissociation of insulin at a high concentration is driven by electrostatic repulsion and hydrophobic interaction resulting from bile salt binding, and occurs at a concentration lower than the critical micelle concentration of bile salts. We suggest that the interaction between insulin and the bile salt occurs by hydrophobic binding followed by a poorly cooperative binding process with an increasing concentration of bile salts. In addition, the bile salt binding to the surface of insulin alters not only the microenvironment around tyrosine residues but also the conformation of insulin to some degree, which probably resulted from the dissociation of insulin. However, no notable loss of structure happens to insulin during all the processes under our experimental conditions. A mechanism of bile salt binding to insulin and bile salt-mediated dissociation of insulin oligomers is proposed whereby hydrophobic interaction and electrostatic repulsion happen between them. This work also showed that the combination of these spectroscopic studies is a powerful tool to clarify the interactions between these surfactants and proteins.
Keywords: Insulin; Bile salt; Conformation; Dissociation; Protein–surfactant interaction
Investigation of the possibility of low pressure encapsulation of carbon dioxide in potassium chabazite (KCHA) and sodium chabazite (NaCHA) zeolites
by Firas N. Ridha; Paul A. Webley (pp. 332-337).
Low pressure hysteresis is observed and modeled forCO2 adsorption in potassium chabazite zeolite.Adsorption and desorption equilibrium isotherms ofCO2 on lithium chabazite (LiCHA), sodium chabazite (NaCHA) and potassium chabazite (KCHA) zeolites were measured at 273K up to 103kPa using a volumetric method. The effect of cation type, and hence the structure of the chabazite cavities on the adsorption behavior was revealed through the analysis of isotherm branches. Low pressure hysteresis loops were observed on NaCHA and KCHA demonstrated by residuals of 0.37 and 0.57moleculecavity−1 at pressures of 0.04 and 0.09kPa, respectively. Hysteresis loops commenced at pressures of 0.86kPa on NaCHA and 1.05kPa on KCHA. The earlier appearance of the hysteresis loop on KCHA over that on NaCHA suggested a higher extent of blockage of the 8-ring window aperture byK+ cations. Low pressure hysteresis loops in molecular sieves zeolites reflect the intriguing possibility of encapsulation. A quadrupolar interaction potential was used in the formulation of an encapsulation model utilizing the statistical theory of the radial distribution function (rdf) and the theory of a perfect 3D lattice gas. The model was validated with published literature data using the Lennard-Jones potential. However, both models underestimated the number ofCO2 molecules in the cavities of the chabazite. Including the interaction terms ofCO2–CO2 andCO2-host cavity pairs may improve the prediction of the model. The cavity’s dimensions and portals can be carefully designed to achieve greater selectivities in gas separation and stabilities in gas storage.
Keywords: Adsorption; Chabazite; Zeolite; Gas encapsulation; Carbon dioxide
Predicted models for phenanthrene sorption nonlinearity and capacity based on different HA/BC ratios in sediments
by Jinghuan Zhang; Mengchang He (pp. 338-344).
About 85% of the reported n values fall into the 90% confidence interval of the exponential model, indicating the practicability of the model in prediction of Phen sorption nonlinearity.Phenanthrene (Phen) sorption isotherms for synthetic sediment organic matter samples with nine different humic acid/black carbon (HA/BC) ratios were determined to provide predicted models for Phen sorption nonlinearity and affinity by sediments. The sorption data were fitted well by the Freundlich model. The nonlinear sorption of Phen was dominated by BC particles. According to BC/TOC content, Phen sorption nonlinearity can be predicted using the exponential model: n=0.410+0.454∗exp(−0.028 BC/TOC). As sorption is a combination of absorption into soft carbon and adsorption onto hard carbon, based on published KHA, KFBC, and nbc values and measured fBC and foc values, Phen sorption affinity-related parameter Koc values can be predicted from the simplified dual sorption model:focKoc=(foc-fBC)KHA+fBCKFBCCenbc-1. For sediments from the Song–Liao watershed (China), the exponential model and dual sorption model gave good predictions for n and Koc values, which support the availability of the two predicted models.
Keywords: Predicted model; Sorption; Phenanthrene; Humic acid; Black carbon; Sediment
Adsorption studies on the removal of coloring agent phenol red from wastewater using waste materials as adsorbents
by Alok Mittal; Dipika Kaur; Arti Malviya; Jyoti Mittal; V.K. Gupta (pp. 345-354).
Effect of pH on the uptake of phenol red by bottom ash and deoiled soya.Bottom ash, a waste of thermal power plants, and deoiled soya, an agricultural waste material, were employed for successful removal and recovery of hazardous phenol red dye from wastewaters. The adsorption characteristics and operational parameters were determined by monitoring different parameters such as effect of pH, effect of concentration of the dye, amount of adsorbents, contact time, and temperature. The equilibrium data were analyzed on the basis of various adsorption isotherm models, namely Langmuir, Freundlich, Tempkin, and Dubinin–Radushkevich. The highest monolayer adsorption capacity has been obtained for the phenol red-bottom ash system (2.6×10−5mol/g) at 50°C. Different thermodynamic parameters such as free energy, enthalpy, and entropy have been calculated and it was concluded that with the increase in temperature adsorption increases, indicating the endothermic nature of the process for both adsorbent materials. Kinetic parameters were derived from pseudo-first-order and pseudo-second-order kinetics. Differentiation between particle and film diffusion mechanisms operative in the present study has been carried out. The column regeneration characteristic has been also investigated and recovery percentage greater than 90% was obtained for both adsorbents by utilizing acidic eluent.
Keywords: Adsorption; Bottom ash; Deoiled soya; Phenol red; Dye
Specific thermodynamical potentials on surfaces under relativistic conditions
by E.V. Veitsman (pp. 355-357).
A flat moving plane;v→c;v is its velocity, c is the light velocity.Expressions of specific thermodynamical potentials on surfaces(J/cm2) were obtained (for internal energy, enthalpy, free energy, and free enthalpy) under relativistic conditions.
Keywords: Thermodynamical potential; Surface; Relativistic conditions
Peptides for functionalization of InP semiconductors
by Elias Estephan; Marie-belle Saab; Christian Larroque; Marta Martin; Fredrik Olsson; Sebastian Lourdudoss; Csilla Gergely (pp. 358-363).
New method for selective functionalization of InP surface using a specific peptide: fluorescence microscopy reveals specific attachment of the biotinilated peptide directed FITC-labelled streptavidin adsorption onto the InP pattern and not on the SiO2 area.The challenge is to achieve high specificity in molecular sensing by proper functionalization of micro/nano-structured semiconductors by peptides that reveal specific recognition for these structures. Here we report on surface modification of the InP semiconductors by adhesion peptides produced by the phage display technique. An M13 bacteriophage library has been used to screen 1010 different peptides against the InP(001) and the InP(111) surfaces to finally isolate specific peptides for each orientation of the InP. MALDI-TOF/TOF mass spectrometry has been employed to study real affinity of the peptide towards the InP surfaces. The peptides serve for controlled placement of biotin onto InP to bind then streptavidin. Our Atomic Force Microscopy study revealed a total surface coverage of molecules when the InP surface was functionalized by its specific biotinylated peptide (YAIKGPSHFRPS). Finally, fluorescence microscopy has been employed to demonstrate the preferential attachment of the peptide onto a micro-patterned InP surface. Use of substrate specific peptides could present an alternative solution for the problems encountered in the actually existing sensing methods and molecular self-assembly due to the unwanted unspecific interactions.
Keywords: Functionalization; Bacteriophage; Specific peptide; Semiconductors; Mass spectroscopy
Admicellar polymerization of methyl methacrylate on aluminum pigments
by Philip M. Karlsson; Neo B. Esbjörnsson; Krister Holmberg (pp. 364-368).
Adsolubilization and subsequent polymerization of methyl methacrylate inside the hydrophobic domain of a surfactant bilayer, adsorbed on an alumina surface in aqueous solution.Micrometer-sized aluminum particles used as pigments in silver inks and coatings are reactive in water-based formulations. This leads to hydrogen gas evolution in the paint containers and loss of the silvery appearance of the coating. The protection of aluminum pigments from water is called inhibition and it was shown in earlier work that anionic surfactants of the phosphate ester type are effective as inhibitors, forming a protective bilayer on the aluminum pigment surface. In this work, the protection of aluminum pigments has been extended by means of an encapsulating polymer layer. A poly(methyl methacrylate) (PMMA) coating was applied on aluminum pigment particles by admicellar polymerization of methyl methacrylate. A surfactant is first adsorbed on the aluminum pigment surface and a hydrophobic monomer and initiator is subsequently solubilized inside the hydrophobic domain of the surfactant aggregates that cover the pigment. Diffuse Reflective Infrared Fourier Transform (DRIFT) spectrometry showed that PMMA was formed on the pigment particles and the amount of organic material was up to 24% of the particle weight, as measured by Thermo Gravimetric Analysis (TGA). A hydrophobic initiator, such as benzoyl peroxide, gave good results but the hydrophilic sodium persulfate resulted in poor yield of encapsulating polymer. Sodium dodecyl sulfate, which by itself is not an efficient inhibitor, was used as surfactant. Good results were obtained in terms of protection from an alkaline solution, indicating that the polymer coating per se is an efficient inhibitor. The highest amount of polymer formed on the pigment surface was obtained when the surfactant concentration was around the CMC.
Keywords: Aluminum pigment; Admicellar polymerization; Poly(methyl methacrylate); Inhibition; Water-borne; Coating
Observations of the distribution of GM3 in membrane microdomains by atomic force microscopy
by Kazutoshi Iijima; Norihiro Soga; Teruhiko Matsubara; Toshinori Sato (pp. 369-374).
The segregation of a GM3 domain in another phase was indicated by the AFM-based observation of reconstituted membrane of lipid extracts from B16 membrane cells and artificial membrane.Glycosphingolipids (GSLs) in membrane microdomains participate in important biological functions. In the present paper, we propose a novel model of the distribution of GSLs in membrane microdomains composed of sphingomyelin (SM) and cholesterol. We investigated the distribution of the ganglioside GM3 in a lipid membrane reconstituted with lipid extract from mouse B16 melanoma cells using an atomic force microscope (AFM). The surface topography of the reconstituted lipid bilayer showed three areas of different heights. The highest area was confirmed to be a GM3 domain by labeling with wheat germ agglutinin. To identify the lipids which are contributed to make the topography, the topographies of the artificial lipid bilayers composed of GM3, SM, 1-palmitoyl-2-oleoyl-phosphatidylcholine, and cholesterol were investigated. AFM images of the artificial lipid bilayers showed that the GM3 domain surrounded by a SM-containing phase only occurred, and its formation was found to depend on the cholesterol content.
Keywords: Abbreviations; Glc; glucose; Gal; galactose; GalNAc; N; -acetylgalactosamine; Neu5Ac; N; -acetylneuraminic acid; Cer; ceramide; GSL; glycosphingolipid; GM3; Neu5Acα2–3Galβ1–4Glcβ1–1’Cer; GM1; Galβ1–3GalNAcβ1–4(Neu5Acα2–3)Galβ1– 4Glcβ1–1’Cer; AFM; atomic force microscope; POPC; 1-palmitoyl-2-oleoyl-phosphatidylcholine; SM; sphingomyelin; WGA; wheat germ agglutinin; HPTLC; high performance thin-layer chromatography; CTB; cholera toxin B subunit; GEM; glycosphingolipid-enriched microdomain; MDCK; Madin–Darby canine kidney; l; o; liquid-ordered phase; l; d; liquid-disordered phase; s; o; solid-ordered phaseMembrane microdomain; Glycosphingolipid; Atomic force microscope; Lipid raft
Spraying spin coating silanization at room temperature of a SiO2 surface for silicon-based integrated light emitters
by C. Cherkouk; L. Rebohle; W. Skorupa; T. Strache; H. Reuther; M. Helm (pp. 375-380).
A new silanization method for SiO2 surfaces has been developed for Si-based light emitters which are intended to serve as light sources in smart biosensors relying on fluorescence analysis.A new silanization method for SiO2 surfaces has been developed for Si-based light emitters which are intended to serve as light sources in smart biosensors relying on fluorescence analysis. This method uses a special silanization chamber and is based on spraying and spin coating (SSC) in nitrogen atmosphere at room temperature for 10min. It avoids processes like sonication and the use of certain chemicals being harmful to integrated light emitters. The surface of a SiO2 layer serving as a passivation layer for the light emitters was hydrolyzed to silanols using an in situ-hybridization chamber and catalyzed with MES (2-( N-morpholino)ethanesulfone acid hydrate) buffer solution. Subsequently, the substrates were silanized with the SSC method using two coupling agents as (3-Aminopropyl)trimethoxysilane (APMS), and N′-(3-(trimethoxysilyl)-propyl)-diethylenetriamine (triamino-APMS).The structure of the SiO2 surface, the APMS and the triamino-APMS layers was controlled and characterized by Infrared spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. The results show a covalent binding of the silane coupling agents on the surface. Atomic force microscopy was used to investigate the roughness of the surface. The silanized samples exhibit smooth and densely covered surfaces. Finally, the suitability of the SSC method was verified on real light emitters.
Keywords: Si-based light emission; Estrogen; Biosensors; X-ray photoelectron spectroscopy; Atomic force microscopy; APMS; Silanol; Silanization
Physical and chemical effects of extracellular polymers (EPS) on Zn adsorption to Bacillus licheniformis S-86
by Janette Tourney; Bryne T. Ngwenya; J.W. Fred Mosselmans; Marisa Magennis (pp. 381-389).
Production of extracellular polymers (EPS) affects the physical (aggregation) behaviour of bacterial cells, but not the Zn adsorption mechanisms.This study investigated Zn adsorption to an extracellular polymeric substance (EPS)-producing bacterial strain, Bacillus licheniformis S-86. Batch metal adsorption experiments and spectroscopic (EXAFS) analysis were conducted using both native (EPS-covered) cells and EPS-free cells in order to assess the contribution made by EPS to metal adsorption by this strain. Thermodynamic modelling of the macroscopic adsorption data indicated that Zn complexation to both native and EPS-free cells was predominantly to carboxyl(pKa5.3–5.4) and phosphate(pKa7.4–7.5) functional groups, but with some adsorption to phosphodiester(pKa3.3–3.4) groups also evident. EXAFS analysis shows Zn-carboxyl complexation, but possibly with a significant contribution from a second, phosphate functional group. Apparently, EPS removal does not affect the metal adsorption capacity at the metal: biomass ratios used here. As the concentration of carboxyl and phosphate functional groups is only slightly affected by EPS extraction, complexation to these functional groups explains why EPS removal does not reduce the amount of Zn adsorbed by the cells. It was also observed that EPS production induces aggregation of cells in suspension. This may reduce the cell surface area available for metal adsorption, thus counteracting any greater availability of metal-complexing ligands in the EPS layer compared to an EPS-free cell surface. Furthermore, the EPS layer appears to be the major source of dissolved organic carbon (DOC) released to solution during the metal adsorption experiments. This DOC may reduce metal binding to the cell surfaces by acting as a competing complexing ligand. These observations have implications for industrial application of biofilms and suggest that over-production of EPS in bio-reactors may reduce the metal removal efficiency of the biomass.
Keywords: Bacteria; EPS; Metal adsorption; Zn; EXAFS
Calorimetric measurements of proton adsorption onto Pseudomonas putida
by Drew Gorman-Lewis (pp. 390-395).
Exothermic heats produced by proton adsorption onto the Pseudomonas putida bacterial surface.Having an understanding of the reactive nature of the bacterial surface is enhanced when its reactivity is considered in a thermodynamic framework. Towards this end, isothermal titration calorimetry was used to measure heats of proton adsorption onto Pseudomonas putida, a common Gram negative soil bacterium. Proton adsorption generated large exothermic heats and proton uptake continued down to pH 2.5. Applying a surface complexation model to the calorimetric data allowed for the derivation of site-specific enthalpies and entropies of proton adsorption. The 4-site non-electrostatic model of Borrok et al. [D.M. Borrok, J.B. Fein, J. Colloid Interface Sci. 286 (2005) 110] was chosen to describe proton adsorption and enabled derivation of site-specific enthalpies of −2.4±0.3, −3.7±0.2, −9.0±0.6, and −36.0±1.2kJ/mol for Sites 1–4, respectively. Entropies of proton adsorption were calculated to be 51±3, 75±1, 91±2, and 55±4J/molK, for Sites 1–4, respectively. Enthalpies and entropies of Sites 1 and 3 are consistent with that of multifunctional organophosphonic acids, Site 2 is consistent with multifunctional carboxylic acids, and Site 4 is consistent with an amine. Temperature dependence of the acidity constants for Sites 1–3 is predicted to be minimal; however, Site 4 is predicted to more substantially affected by temperature.
Keywords: Bacterial adsorption; Surface complexation; Enthalpy; Entropy; Calorimetry; Gram negative
The impact of nanoscale chemical features on micron-scale adhesion: Crossover from heterogeneity-dominated to mean-field behavior
by Ranojoy Duffadar; Surachate Kalasin; Jeffrey M. Davis; Maria M. Santore (pp. 396-407).
Particle interactions with a heterogeneous surface comprise electrostatic, van der Waals, and hydrodynamic forces. Spatial fluctuations in the randomly-distributed nanoscale attractors create hot spots which capture flowing particles.This work explores the impact of nanoscale surface heterogeneity, small relative to the effective contact area between two surfaces, on pairwise colloid-scale interactions. Polycation-based positive patches, of order 10nm in diameter, arranged randomly and lying flat on otherwise negative substrates, were used to create surfaces whose competing attractive and repulsive features determined the net interactions with opposing surfaces. Lab experiments and simulations of the adhesion of gently flowing dilute negative microparticles varied particle size (0.5–2μm), ionic strength ( κ−1=1–12nm) and the density of heterogeneity on the collectors. Limiting behaviors from heterogeneity-controlled at high ionic strength to mean-field-like interactions at low ionic strength are reported. When heterogeneities are important, pairwise interactions are more attractive than predicted by average surface properties (e.g. per DLVO), and an adhesion threshold, describing the minimum average density of cationic features needed for single particle capture (adhesion), depends strongly on Debye length. In the opposite limit, the threshold becomes insensitive to the Debye length, and the average surface character approximates the interactions. An analytical treatment, reduced to a simple scaling argument predicts a −1/2 power-law dependence of the adhesion threshold on Debye length and particle size. A slightly stronger particle size dependence in experiments and simulations results from hydrodynamic contributions along with slight scaling differences in electrostatic, van der Waals, and hydrodynamic forces. An analogy to biological ligands is made for the heterogeneity-dominated limit: it is discovered, for this particular system, that engagement of as few as 20–100 cationic patches dictates particle adhesion (with details depending on flow, particle size, and ionic strength), similar to reports for selectin-mediated rolling of white blood cells during the inflammatory pathway. Also discovered is a heterogeneity-dependent crossover in the effect of ionic strength on particle capture, where added salt promotes particle adhesion in most cases but stabilizes the particles when the heterogeneity becomes relatively dense.
Keywords: Interparticle force; Flocculation; Aggregation kinetics; Heterogeneity; Patchy surfaces; Heteroflocculation; Bacterial adhesion
Characteristics of BPA removal from water by PACl-Al13 in coagulation process
by Ma Xiaoying; Zeng Guangming; Zhang Chang; Wang Zisong; Yu Jian; Li Jianbing; Huang Guohe; Liu Hongliang (pp. 408-413).
This paper discussed the coagulation characteristics of BPA with polyaluminum chloride (PACl-Al13) as coagulant, examined the impact of coagulation PACl-Al13 dosage as the figures shown, and parameters such as pH, TOC and turbidity on BPA removal were also investigated.This paper discussed the coagulation characteristics of BPA with polyaluminum chloride (PACl-Al13) as coagulant, examined the impact of coagulation pH, PACl-Al13 dosage, TOC (total organic carbon) and turbidity on BPA removal, and analyzed the possible dominant mechanisms in water coagulation process. Formation and performance of flocs during coagulation processes were monitored using photometric dispersion analyzer (PDA). When the concentration of humic acid matters and turbidity was low in the solution, the experimental results showed that the removal of BPA experienced increase and subsequently decrease with the PACl-Al13 dosage increasing. The optimal PACl-Al13 dosage was found at BPA/PACl-Al13=1:2.6(M/M) under our experiment conditions. Results show that the maximum BPA removal efficiency occurred at pH 9.0 due to the adsorption by Al13 aggregates onto BPA rather than charge neutralization mechanism by polynuclear aluminous salts in the solution. The humic acid matters and kaolin in the solution have significant effect on BPA removal with PACl-Al13 in the coagulation. The BPA removal will be weakened at high humic matters. The removal rate of BPA increased and subsequently decreased with the turbidity increasing.
Keywords: Bisphenol A; PACl-Al; 13; Coagulation; Floc
Synthesis of highly fluorescent glutathione-capped Zn xHg1− xSe quantum dot and its application for sensing copper ion
by Fang-Chen Liu; Yi-Ming Chen; Jia-Hui Lin; Wei-Lung Tseng (pp. 414-419).
Synthesis of glutathione-capped Zn xHg1− xSe quantum dots has been accomplished by reacting a mixture of Zn(ClO4)2 and Hg(ClO4)2 with NaHSe and using glutathione as surface-stabilizing agent.A one-step synthesis of glutathione-capped Zn xHg1− xSe quantum dots (QDs) has been accomplished by reacting a mixture of Zn(ClO4)2 and Hg(ClO4)2 with NaHSe and using glutathione as surface-stabilizing agent. The fluorescent color of the alloyed QDs could be tuned by varying the Zn2+:Hg2+ molar ratio, reaction pH, intrinsic Zn2+ and Hg2+ reactivity toward NaHSe, and the concentration of NaHSe. The size, composition, and inner structures of these QDs are characterized using dynamic light scattering, inductively coupled plasma-mass spectrometry, and X-ray powder diffraction. By varying the molar ratio of Zn2+ to Hg2+ in the precursor solution, the Zn xHg1− xSe QDs exhibited a tunable PL wavelength in the range of 548–621nm. These QDs offered advantages of short reaction time (1h), low reaction temperature (95°C), high quantum yield, water solubility and biocompatibility. Additionally, glutathione-capped Zn0.96Hg0.04Se QDs (quantum yield=78%) have been applied for sensing Cu2+.
Keywords: Alloyed quantum dots; Glutathione; Sensor; Copper
Facile synthesis of mesoporous SBA-15 silica spheres and its application for high-performance liquid chromatography
by Huihui Wan; Lin Liu; Cunman Li; Xingya Xue; Xinmiao Liang (pp. 420-426).
Large-pore SBA-15 silica spheres have been synthesized and explored as stationary phase in reversed-phase high-performance liquid chromatography. High-performance chromatographic separation of small molecules and relatively large bio-molecules have been obtained on the octadecyl modified SBA-15 silica column with partilce size of 4.5μm.Micrometer-sized mesoporous SBA-15 silica spheres have been synthesized using triblock copolymer poly(ethyleneoxide)-block-poly(propyleneoxide)-block-poly(ethyleneoxide) (EO20PO70EO20) as structure-directing agent with the assistance of 1,3,5-trimethylbenzene and KCl. By controlling the composition of synthesis gel, SBA-15 silica spheres with particle size in the range of 2–4.5μm could be facilely obtained. The obtained SBA-15 silica spheres were characterized by X-ray diffraction, scanning electron microscopy, and N2 physisorption technique. Dimethyloctadecylchlorosilane modified mesoporous SBA-15 silica with diameter of 4.5μm was explored as stationary phase in high-performance liquid chromatography, and its chromatographic characteristics for separation of some small molecules and relatively large bio-molecules have been studied.
Keywords: Mesoporous; SBA-15 silica; Spheres; Stationary phase
In situ time-resolved XAFS analysis of silver particle formation by photoreduction in polymer solutions
by Masafumi Harada; Yasuhiro Inada; Masaharu Nomura (pp. 427-438).
Time evolution of the X-ray absorbance μ( E) as a function of X-ray energy E and the representative TEM image for the colloidal dispersions of Ag particles prepared by the photoreduction in the presence of benzoin.Formation mechanisms of silver (Ag) particles in an aqueous ethanol solution of poly( N-vinyl-2-pyrrolidone) (PVP) by the photoreduction of AgClO4 were investigated by using UV–Vis, transmission electron microscopy (TEM), extended X-ray absorption fine structure (XAFS), and in situ energy-dispersive X-ray absorption fine structure (in situ DXAFS) measurements. The average diameter of the Ag particles prepared in the presence and absence of benzoin as a photo-activator was estimated from TEM to be 7.4 and 5.1nm, respectively, and their particle size distributions ranged from 2 to 15nm. XAFS analysis indicated that metallic Ag particles were synthesized, and the reduction rate of Ag+ to Ag0, the creation of Ag0–Ag0 bonds and their particle growth by the association of Ag0–Ag0 was regulated by the metal concentration and the inclusion of benzoin. In situ DXAFS measurements were performed in real time to investigate the kinetics of Ag+ reduction and Ag particle formation. During the induction period the reduction of Ag+ to Ag0 occurred, and subsequent nucleation and growth process concurrently proceeded after the induction period. The intermediate small Ag particles (C.N. smaller than about 4) were generated in the nucleation process, and grown up to larger particles (C.N.s equal to 4.5±1.5) in the longer-duration photoreduction.
Keywords: Colloidal dispersions; Silver particles; Polymer-stabilized particles; Photoreduction; Particle formation; XAFS; In situ DXAFS
pH-dependent surface charging and points of zero charge. IV. Update and new approach
by Marek Kosmulski (pp. 439-448).
Specimens of goethite, for which PZC/IEP has been reported.The recently published points of zero charge (PZC) and isoelectric points (IEPs) of various materials are compiled to update the previous compilation [M. Kosmulski, Surface Charging and Points of Zero Charge, CRC Press, Boca Raton, FL, 2009]. Unlike in previous compilations by the same author [Chemical Properties of Material Surfaces, Dekker, New York, 2001; J. Colloid Interface Sci. 253 (2002) 77; J. Colloid Interface Sci. 275 (2004) 214; J. Colloid Interface Sci. 298 (2006) 730], the materials are sorted not only by the chemical formula, but also by specific product, that is, by brand name (commercially available materials), and by recipe (home-synthesized materials). This new approach indicated that the relatively consistent PZC/IEP reported in the literature for materials having the same chemical formula are due to biased choice of specimens to be studied. Specimens which have PZC/IEP close to the “recommended” value are selected more often than other specimens (PZC/IEP not reported before or PZC/IEP reported, but different from the “recommended” value). Thus, the previously published PZC/IEP act as a self-fulfilling prophecy.
Keywords: Point of zero charge; Isoelectric point; Surface charge density; Zeta potential; Electrokinetic potential
Determination of isoelectric points of metals and metallic alloys by adhesion of latex particles
by Grégory Lefèvre; Ljiljana Čerović; Slobodan Milonjić; Michel Fédoroff; Jörgen Finne; Anne Jaubertie (pp. 449-455).
Influence of pH on concentration of negative latex particles in contact with metallic alloys. Dotted lines are extrapolations to determine the isoelectric points of surfaces.A set-up and a method were developed to determine the isoelectric point of metals and metallic alloys samples (stainless steels, inconel, zircaloy, aluminum and dural) by measuring the adhesion rate of negative latex particles. The concentration of polystyrene spheres with surface carboxylate groups (initially 0.5–1mgL−1) in contact with metallic samples was measured as a function of pH and time by turbidimetry. The simulation of measurements by a model predicting the sticking coefficient based on DLVO theory was used for the determination of the isoelectric point from experimental results. It was found that the isoelectric points of aluminum (8.7) and dural (9.1), treated by boiling water, are close to those of hydrated aluminum oxides powders. For stainless steels, inconel and zircaloy, the values of isoelectric points were found to be between 2.4 and 3.0, far below the isoelectric points measured for metallic oxides constituting the alloy surface layer. This difference was explained by two different charging mechanisms: (1) deprotonation of hydroxyl groups on the surface of the metal oxide in suspension or as a thick layer, (2) adsorption of hydroxide ions on a metal surface covered by a thin oxide layer, as observed on hydrophobic surfaces.
Keywords: Turbidimetry; Fouling
Barium hexaferrite suspensions for electrophoretic deposition
by Simona Ovtar; Darja Lisjak; Miha Drofenik (pp. 456-463).
Schematic presentation of electrophoretic deposition from stabile suspension of hard-magnetic particles.In this investigation we have looked at the preparation of barium hexaferrite suspensions, with the stability of the magnetic barium hexaferrite particles being increased by the addition of a surfactant, dodecylbenzylsulfonic acid (DBSA). The influence of the solubility DBSA in different solvents and its adsorption onto the surfaces of particles with different sizes were determined from zeta-potential measurements. The most suitable and stable suspensions of barium hexaferrite particles, regardless of their sizes, were obtained in 1-butanol, and these were then used for a subsequent electrophoretic deposition. The microstructures of the deposits were examined with electron microscopy. The thickness and density of the deposits as a function of the electric field, the zeta-potential, the particle size, and the separation distance between the electrodes were investigated. The thickness of the deposits was found to increase with the increasing zeta-potential of the suspension and with the increasing separation distance between the electrodes. Denser deposits were obtained from the suspensions of smaller particles that had narrower particle size distributions.
Keywords: Barium hexaferrite; Stable magnetic suspension; Adsorption; Electrophoretic deposition
Stability of binary and ternary model oil-field particle suspensions: A multivariate analysis approach
by Dorota Dudášová; Geir Rune Flåten; Johan Sjöblom; Gisle Øye (pp. 464-471).
Measured (thin lines) and predicted (thick lines) transmission spectra for aqueous suspensions containing asphaltene-coated particles measured at 50 °C for 75min. Transmission profiles were analyzed by multivariate methods.The transmission profiles of one- to three-component particle suspension mixtures were analyzed by multivariate methods such as principal component analysis (PCA) and partial least-squares regression (PLS). The particles mimic the solids present in oil-field-produced water. Kaolin and silica represent solids of reservoir origin, whereas FeS is the product of bacterial metabolic activities, and Fe3O4 corrosion product (e.g., from pipelines). All particles were coated with crude oil surface active components to imitate particles in real systems. The effects of different variables (concentration, temperature, and coating) on the suspension stability were studied with Turbiscan LA b Expert. The transmission profiles over 75min represent the overall water quality, while the transmission during the first 15.5min gives information for suspension behavior during a representative time period for the hold time in the separator. The behavior of the mixed particle suspensions was compared to that of the single particle suspensions and models describing the systems were built. The findings are summarized as follows: silica seems to dominate the mixture properties in the binary suspensions toward enhanced separation. For 75min, temperature and concentration are the most significant, while for 15.5min, concentration is the only significant variable. Models for prediction of transmission spectra from run parameters as well as particle type from transmission profiles (inverse calibration) give a reasonable description of the relationships. In ternary particle mixtures, silica is not dominant and for 75min, the significant variables for mixture (temperature and coating) are more similar to single kaolin and FeS/Fe3O4. On the other hand, for 15.5min, the coating is the most significant and this is similar to one for silica (at 15.5min). The model for prediction of transmission spectra from run parameters gives good estimates of the transmission profiles. Although the model for prediction of particle type from transmission parameters is able to predict some particles, further improvement is required before all particles are consistently correctly classified. Cross-validation was done for both models and estimation errors are reported.
Keywords: Particles; Suspension stability; Produced water; Surface modification; Turbiscan; Multivariate analysis; PLS
SANS investigation of the microstructures in catanionic mixtures of SDS/DTAC and the effect of various added salts
by Sylvain Prévost; Michael Gradzielski (pp. 472-484).
Small-Angle Neutron Scattering is used to reveal the microstructures formed in the aqueous catanionic mixtures of SDS and DTAC.The aggregation behavior of two common ionic surfactants with opposite charges, sodium dodecylsulfate (SDS) and dodecyltrimethylammonium chloride (DTAC), was studied for their mixtures and for different added salts. The aggregates formed were characterized by means of small-angle neutron scattering (SANS), at two temperatures: 25 and 50°C (below and above the “Krafft point” of the catanionic salt) and at two overall concentrations (50 and 200mM). Results have been compared to the well-known SDS+DTAB system. Similar results are found, showing that with no excess of salt the nature of the counter-ion, bromide or chloride, has no dominant effect on this mixture of oppositely charged surfactants. Further SANS experiments were carried out to check the effect of ions on the pure surfactants, the ions being chosen to mimic the head group of the paired surfactant in the catanionic mixture. Tetramethylammonium chloride (TMACl) was added to SDS and sodium methylsulfate (SMS) to DTAC. Their effects were compared to NaCl, which was included in this study as a reference, and explained in terms of competition between the behavior of simple ions (screening) and that of a “binding ion” (attachment to the micellar surface). Apparently the effect of salt addition to these two surfactants is clearly strongly ion-specific.
Keywords: Catanionic; SDS; DTAC; Specific ion effect; Small-angle neutron scattering
Comparative study of thiol-free amphiphilic hyperbranched and linear polymers for the stabilization of large gold nanoparticles in organic solvent
by Qiang Tang; Fa Cheng; Xing-Long Lou; Hua-Ji Liu; Yu Chen (pp. 485-491).
Amphiphilic hyperbranched polymers showed better ability to extract and stabilize the citrate-protected large gold nanoparticles into chloroform than their corresponding linear analogs.Amphiphilic hyperbranched and linear polymers based on the respective palmitic acid modified hyperbranched and linear polyethylenimines have been successfully employed to transfer the citrate-protected 17-nm gold nanoparticles (AuNPs) from water into chloroform without the aid of other compounds. Compared with their corresponding linear analog, the amphiphilic hyperbranched polymers exhibited higher efficiency in transferring the large AuNPs. The chloroform solutions of AuNPs were characterized by UV–vis spectrometry and dynamic light scattering. It was found that aggregated AuNPs existed in the system with the amphiphilic linear polymer as stabilizer, whereas much less aggregated AuNPs could be detected in the system with the amphiphilic hyperbranched polymer as stabilizer. Furthermore the amphiphilic hyperbranched polymers could form relatively homogeneous and densely packed shell around the gold core revealed by transmission electron microscopy. Stability experiments showed that the solution of AuNPs coated with the amphiphilic hyperbranched polymers were more stable than those coated with their linear analogs. Moreover, the AuNPs capped with the amphiphilic hyperbranched polymers could be also stored in dryness for long time.
Keywords: Amphiphilic; Gold nanoparticle; Hyperbranched polymer; Phase transfer; Polyethylenimine
Ferrihydrite reactivity toward carbon dioxide
by Douglas B. Hausner; Narayan Bhandari; Andro-Marc Pierre-Louis; James D. Kubicki; Daniel R. Strongin (pp. 492-500).
Varying concentrations of CO2 react with 2–6nm ferrihydrite particles resulting in the formation of surface adsorbed bicarbonate-like species. The effect of surface hydration on adsorbate speciation is addressed.The reaction of ferrihydrite with gaseous CO2 was investigated with attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and density functional theory (DFT) calculations. ATR-FTIR results show that CO2 reacts with ferrihydrite resulting in surface adsorbed carbonate species. The carbonate species experimentally observed in view of theoretical calculations are shown to be in large part monodentate binuclear complexes. These carbonate complexes exist as both inner-sphere and outer-sphere hydrogen-bonded complexes. Under “dry” conditions CO2 reacts with free OH sites on the ferrihydrite surface resulting in a metastable bent CO2 (bicarbonate-like) complex. Removal of the gaseous reactant leads to the loss of this metastable surface complex. The reaction of CO2 with hydrated ferrihydrite results in only carbonate formation (no bicarbonate). In this circumstance, experiments and theoretical calculations suggest that hydrogen bound water on surface OH sites prevents the formation of the metastable bicarbonate species. Ferrihydrite that was allowed to react with atmospheric levels of CO2 and water vapor resulted in the formation of surface carbonate coordinated as both inner and outer-sphere complexes.
Keywords: Ferrihydrite; Carbon dioxide; CO; 2; Carbonate; Adsorption; DFT; ATR-FTIR; HFO; Colloidal ferric hydroxide; Amorphous iron hydroxide
Evaluation of interfacial equilibrium constants from surface potential data: Silver chloride aqueous interface
by Tajana Preočanin; Filip Šupljika; Nikola Kallay (pp. 501-507).
Surface potential at the AgCl aqueous interface as a function of chloride ion activity.A single crystal silver chloride electrode (SCr-AgCl) was used to measure the inner surface potential(Ψ0) at the silver chloride aqueous electrolyte interface as a function of activity of Cl− ions as determined by the Ag/AgCl electrode. Absolute values of the surface potential were calculated from electrode potentials of SCr-AgCl using the value of point of zero charge (pClpzc=5.2) as the value of point of zero potential. Measurements were performed in potassium nitrate aqueous solutions, as well as in the presence of Li, Na, Cs, Mg, and La nitrates. TheΨ0 (pCl) function was found to be linear within the experimental error and practically the same for all the examined electrolytes and almost independent of ionic strength. The reduction of the slope with respect to the Nernst equation, expressed by theα coefficient, was (0.88±0.01) at I c=10−1moldm−3, (0.87±0.01) at I c=10−2moldm−3, and (0.84±0.01) at I c=10−3moldm−3. The results were successfully interpreted by employing the surface complexation model developed originally for metal oxides and adapted for silver chloride. The standard (“intrinsic”) equilibrium constants for the binding of chloride(K°n) and silver ions(K°p) on the corresponding sites at the silver chloride surface were evaluated aslgK°n=2.67±0.05;lgK°p=2.07±0.05. Counterion surface association equilibrium constants were also obtained aslgK°NO3-=lgK°K+=2.74±0.05.
Keywords: Silver chloride; Surface potential; Surface charge; Surface equilibrium constants; Surface complexation model; Single crystal electrode
Determination of diffusion and sorption parameters of thin confined clay layers by direct fitting of through-diffusion flux
by Andriy E. Yaroshchuk; Martin A. Glaus; Luc R. Van Loon (pp. 508-512).
The resulting curves lie clearly outside the error range of experimental data. Thus, the accuracy of determination of the effective diffusion coefficient in clay is better than 30%.Diffusion in compacted clays is often studied in sandwich-like arrangements where the clay is confined by porous filter plates in order to control its swelling. In some clays (for example, Na-montmorillonite) equilibrated with dilute electrolyte solutions, the fluxes of cationic radiotracers can be quite high due to cation-exchange reactions. Accordingly, the diffusion resistance of clay layers can become comparable with or even smaller than the diffusion resistance of porous filters (such layers are called “thin” in this study). In view of the typical uncertainties (ca. 20%) of diffusion permeability of porous filters reported in the literature, the diffusion resistance of clay layers cannot be reliably determined from the steady-state diffusion permeability of the filter–clay–filter “sandwich” in this case. In this study, it is shown that, rather unexpectedly, information on the diffusion permeability of “thin” clay layers can be obtained from the time dependence of diffusant flux into the outlet compartment because at very short times, there is a characteristic flux delay that does not occur in the limiting case of infinitely large diffusion permeability of clay. The flux behavior at longer times is controlled by the diffusion permeability of the filters, which makes possible its determination directly from through-diffusion data and makes superfluous independent diffusion experiments with filters. This approach has been validated via theoretical interpretation of literature data on the diffusion of22Na radiotracers through confined compacted montmorillonite equilibrated with 0.01M NaClO4 solution. The filter and clay properties estimated in this way are in good agreement with the literature data.
Keywords: Non-stationary diffusion; Compacted clay; Porous filter; Effective diffusion coefficient; Sorption capacity
Cu-doped resorcinol–formaldehyde (RF) polymer and carbon aerogels
by Orsolya Czakkel; Erik Geissler; Imre M. Szilágyi; Edit Székely; Krisztina László (pp. 513-522).
Tuned mesopore size distribution of Cu-doped carbon aerogels.Introduction of transition metal salt(s) onto the surface of porous carbons may increase the selectivity and/or efficiency of these adsorbents in catalysis or separation. Carbon aerogels with low pressure drop are particularly suited for these applications. Moreover the sol–gel process used in the synthesis of the resorcinol–formaldehyde polymer gel (RF) precursors offers an extra opportunity for introducing metal ions. Salts of different metals modify both the macroscopic texture and the porosity, depending on the synthesis protocol. In this paper we show, by means of low temperature nitrogen adsorption measurements and SEM, as well as small- and wide-angle X-ray scattering (SAXS and WAXS), how the addition of copper acetate at three different stages influences not only the specific surface area but also the resulting overall structure over a wide range of length scales. Posttreatment in either the polymer or the carbon aerogel stage provides a means of adjusting the copper content. While the Cu-containing carbon aerogels differ mainly in their micropore volume but not in the width of the distribution, their pore size window in the mesopore range can be tuned between 50 and 400Å by the protocol of Cu addition. The synthesis protocol also determines the chemical form of the copper.
Keywords: RF aerogel; Carbon aerogel; SAXS/WAXS; Gas adsorption; Copper; Doping
In situ formation of stable gold nanoparticles in polymer inclusion membranes
by Rakesh Kumar; Ashok K. Pandey; A.K. Tyagi; G.K. Dey; Shobha V. Ramagiri; Jayesh R. Bellare; A. Goswami (pp. 523-530).
Stable 10nm size Au nps have been synthesized in the matrix of plasticized anion-exchange membrane, known as polymer inclusion membrane, using the ion-exchange method. The ion-exchange sites are not affected by the formation of nps in the membrane, leading to the possibility of reusing it.Gold nanoparticles (Au nps) were synthesized in the matrix of a plasticized anion-exchange membrane. The membrane was prepared by solvent casting of the solution containing a liquid anion exchanger trioctylmethylammonium chloride (Aliquat-336), a matrix-forming polymer cellulose triacetate (CTA), and a plasticizer dioctyl phthalate (DOP) dissolved inCH2Cl2. For in situ synthesis of Au nps, the membrane samples were equilibrated with a well-stirred solution containing0.01molL-1HAuCl4.AuCl4- ions were transferred to membrane matrix as an ion pair with Aliquat-336 by an ion-exchange mechanism. In a second step,AuCl4- ion-loaded membrane samples were placed in a well-stirred0.1molL-1 aqueous solution ofNaBH4 for reduction. It was observed that 80% of the anion-exchange sites were readily available for the exchange process after formation of the Au nps. The content of Au nps in the membrane was increased either by increasing the concentration of the Aliquat-336 in membrane or by repeating sequential cycles of loading ofAuCl4- ions followed by reduction withBH4- in the membrane matrix. TEM images of a cross section of the membrane showed that Au nps were dispersed throughout the matrix of the membrane but excluded from the surface. The size distribution of the nps was found to be dependent on Au content in the membrane. For example, 7- to 16-nm Au nps with average size 10nm were observed in the membrane after the first cycle of synthesis. On increasing the Au content in the membrane by repeating the cycle of synthesis, the size dispersion of nps broadened from 5 to 20nm without affecting the average size. Theλmax (530nm) and intensity of the surface plasmon band of Au nps embedded in the matrix of membrane were found to remain unaltered over a testing period of a month in the samples kept in water as well as in air under ambient conditions. This indicated that Au nps were quite stable in the membrane matrix. The experimental information obtained by the radiotracers and energy-dispersive X-ray fluorescence (EDXRF) analyses has been used to understand the process of Au nps formation in the membrane matrix.
Keywords: Ion exchange; Polymer inclusion membrane; Trioctylmethylammonium chloride; Borohydride; Gold nanoparticles
A facile dip-coating process for preparing highly durable superhydrophobic surface with multi-scale structures on paint films
by Zhe Cui; Long Yin; Qingjun Wang; Jianfu Ding; Qingmin Chen (pp. 531-537).
Superhydrophobic surfaces were created on an epoxy paint by sandblasting the paint surface to form microstructures (A), followed by anchoring nano-SiO2 on the microstructure surface to form multi-scale structures (B).Superhydrophobic surfaces with multi-scale nano/microstructures have been prepared on epoxy paint surfaces using a feasible dip-coating process. The microstructures with 5–10μm protuberances were first prepared on epoxy paint surface by sandblast. Then the nanostructures were introduced on the microstructure surface by anchoring 50–100nm SiO2 particles (nano-SiO2) onto the sandblasted paint surface, which was completed by dip-coating with a nano-SiO2/epoxy adhesive solution (M1). At last the surface was further modified for enhancing hydrophobicity by another dip-coating with a solution of a low surface energy polymer, aminopropyl terminated polydimethylsiloxane (ATPS) modified epoxy adhesive (M2). The water contact angle of the as-prepared samples reached as high as 167.8° and the sliding angle was 7°. The prepared superhydrophobic surface exhibited excellent durability to the high speed scouring test and high stability in neutral and basic aqueous solutions and some common organic solvents. In addition, this method can be adopted to fabricate large scale samples with a good homogeneity of the whole surface at very low cost.
Keywords: Superhydrophobic; Multi-scale structure; Epoxy paint; pH and solvent resistance; High speed scouring resistance
Anomalous thickness variation of the foam films stabilized by weak non-ionic surfactants
by Xuan Qu; Liguang Wang; Stoyan I. Karakashev; Anh V. Nguyen (pp. 538-547).
This paper finds anomalous S-shaped thickness variation of the foam films stabilized by various non-ionic surfactants at relatively low surfactant concentrations.The constant thickness ( H) of metastable free films of various non-ionic surfactant solutions was measured at surfactant concentrations less than the critical micelle concentrations or solubility limits with fixed 5×10-5M sodium chloride (NaCl) serving as the background electrolyte. The surfactants include n-pentanol, n-octanol, methyl isobutyl carbinol (MIBC), polypropylene glycol (PPG-400), tetraethylene glycol monooctyl ether (C8E4), and tetraethylene glycol monodecyl ether (C10E4). H was interferometrically measured. For each surfactant in this study, the H-versus-surfactant-concentration curve finds a peak at a concentration around 5×10-6–1×10-5M and a valley at a higher concentration. The measured H values were compared to those predicted from the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory, which considers solely the contribution from electrostatic double-layer repulsion with van der Waals attraction being neglected in the present work. In determining the double-layer repulsion, the ionic strength was determined from the electrolytic conductivity measurement of the film-forming solutions and the surface potential was estimated from theζ-potential measurement of air bubbles. It was found that the DLVO theory failed to explain the thickness variance with surfactant concentration, implying that additional non-DLVO attractive forces might be required to explain the experimental results. Finally, the possible origins of these attractive forces were discussed.
Keywords: Surface force; Flotation frother; Foam films; Hydrophobic force; Dissolved gas
Drainage mechanism of microbubble dispersion and factors influencing its stability
by Wanhua Feng; Naresh Singhal; Simon Swift (pp. 548-554).
Drainage of microbubble dispersion is best described by three phases instead of two as previously assumed in the literature.Microbubble dispersion stability is a desirable characteristic in applications such as separation processes and in-situ bioremediation. This study investigates the effects of surfactant concentration, pH and ionic strength on the stability of dispersions of rhamnolipid, a common anionic biosurfactant. Microbubble dispersions of rhamnolipid and the non-ionic synthetic surfactant tergitol 15-S-12 were prepared by intensive stirring at 8000rpm with solutions of 500–4000mgl−1 surfactant concentration at pH 6–8. The ionic strength tests were performed with 1000–3000mgl−1 sodium chloride. Dispersion stability increases for higher surfactant concentrations, but decreases with rising pH and increasing salt concentration. However, increasing the pH in the co-presence of salt enhances dispersion stability. A modified model showing improved fits to liquid drainage from the dispersions is presented and it is shown that liquid drainage occurs in three distinct phases, instead of two phases as previously assumed in the literature.
Keywords: Colloidal gas aphron; Emulsion; Wet foam; Dry foam; Biosurfactant; Synthetic surfactant; Rhamnolipid; Drainage model; Rate of drainage
Dynamic contact angles on PTFE surface by aqueous surfactant solution in the absence and presence of electrolytes
by Rajib Ghosh Chaudhuri; Santanu Paria (pp. 555-562).
Linear relationship between Teflon–water interfacial tension in the presence of different electrolytes+surfactants ( γSL) and the polar component of the surface tension(γLp).This study presents the experimental results on dynamic contact angles of pure surfactants and surfactants with electrolyte solutions on PTFE (Teflon) surface. Dynamic advancing ( θA) and receding ( θR) contact angles measurements by the Wilhelmy plate technique were carried out for aqueous solution of three different surfactants Triton X-100 (TX-100), sodium dodecylbenzene sulfonate (SDBS), and cetyltrimethylammonium bromide (CTAB). The same measurements in the presence of different electrolytes NaCl, Na2SO4, and CaCl2 for ionic surfactants (SDBS and CTAB) were also carried out to see the change in contact angle and wetting behavior. The presence of electrolytes changes the advancing contact angle as well as wetting properties of hydrophobic solid surface significantly even at very low surfactant concentration. Counter ion valency of the electrolyte is more important in reducing advancing contact angle on hydrophobic PTFE surface at very low concentration of ionic surfactants from CMC. Pure surfactants and ionic surfactants in the presence of electrolytes show a linear relationship between the adhesional tension and surface tension at air–water interface with different slope and intercept.
Keywords: Teflon; Dynamic contact angle; Wetting; Electrolyte
Preparation and properties of comb-like surfactants containing poly(ethylene oxide) methyl ether grafts
by Wei Zhang; Zhiping Du; Chien-Hsiang Chang; Guoyong Wang (pp. 563-568).
Surface tension (mN/m) vs. the log (mass concentration) (g/L) of poly(St-co-MA)-g-(MPEG) solution with different R (▿ 2.6, ▵ 3.9, ○ 5.1) at 29.7±0.1°C. Both critical aggregation concentration (CAC) and surface tension at the CAC ( γCAC) of the poly(St-co-MA)-g-(MPEG)s decrease with increase mole ratio of St to MAMPEG ( R).The comb-like surfactants, poly(styrene-co-maleic anhydride)-g-(poly(ethylene glycol) monomethyl ether), poly(St-co-MA)-g-(MPEG), have been prepared using a macromonomer approach to get controlled molecular structures. The macromonomer (MAMPEG) was obtained by esterification of poly(ethylene glycol) monomethyl ether with maleic anhydride. Poly(St-co-MA)-g-(MPEG) with various molar ratios of St to MAMPEG ( R) were then constructed by radical copolymerization. The comb-like structures of the surfactants were confirmed by infrared and1H nuclear magnetic resonance spectroscopy. It is found from gel permeation chromatography characterization that the molecular weight of the surfactants increases as R increases. The polydispersity index was in the range between 1.4 and 2.0 in all the cases. The surfactants with a higher St percentage are less soluble in water due to aggregation. The value of critical aggregation concentration (CAC) and the surface tension at the CAC ( γCAC) decrease as R increases. The steady-shear measurements show that the surfactant solutions at 50g/L are dilatant fluids. In addition, it appears that there are two break points in the viscosity–shear rate curve. Both break points increase with increasing R. It can therefore be concluded that the properties of comb-like surfactants poly(St-co-MA)-g-(MPEG) are related to molecular structure. The results demonstrate that the properties of these comb-like surfactants can be tailored through appropriate molecular design.
Keywords: Comb-like surfactant; Molecular design; Surface activity; Rheology property; Aggregation behavior
Amphiphile self-aggregation: An attempt to reconcile the agreement–disagreement between the enthalpies of micellization determined by the van’t Hoff and Calorimetry methods
by Satya P. Moulik; Debolina Mitra (pp. 569-578).
The Enthalpy change for amphiphile self-aggregation determined by the van’t Hoff method is different from that found by calorimetry.In this article, discrepancies between the enthalpies of micellization of amphiphiles in aqueous solution determined by the methods of van’t Hoff (VH) and calorimetry have been addressed. The contributions of the hydrophobic interaction, electrostatic interaction and the micellar size effect have been considered to assess the total picture of the amphiphile self-association process and related energetic parameters, especially the enthalpy and the specific heat capacity. Literature results on 23 amphiphile systems (six nonionics, five anionics, and twelve cationics) have been analyzed, and the assessed enthalpies by VH method and direct calorimetry have been presented and compared. VH results considering participation of 5% of total amphiphile monomer to form micelle at cmc have been also compared. In addition to this, the changes in the standard specific heat of micellization for all the amphiphile aggregation processes evaluated by the VH and calorimetry procedures have been presented. The differences between the standard enthalpy of micellizationΔHm° by the methods of VH and calorimetry are minor for nonionic surfactants but major for ionics, whereas the standard specific heat capacities of micellizationΔCpm° by both the procedures fairly agree for all types of surfactants. LikeΔHm°-ΔSm° compensation observed in kinetic and equilibrium processes, a linear correlation betweenLtT→0ΔHm° andΔCpm° has been observed with no distinction between the VH and calorimetry derived results for all the surfactant systems herein dealt with.
Keywords: Amphiphile; Micellization; Enthalpy; van’t Hoff; Microcalorimetry
Role of the co-surfactant nature in soybean w/o microemulsions
by Carla R.B. Mendonça; Yara P. Silva; Wolmir J. Böckel; Ernesto F. Simó-Alfonso; Guillermo Ramis-Ramos; Clarisse M.S. Piatnicki; Clara I.D. Bica (pp. 579-585).
Co-surfactants play important roles in microemulsions properties such as electrical conductivity and droplet size which, beyond giving fundamental information on these system hydrodynamics, allow characterization of vegetable oils by electroanalytical techniques.The influence of the co-surfactant on physicochemical properties of w/o soybean oil microemulsions (MEs) has been studied. In spite of the similarity in phase diagrams, the MEs display remarkable differences when examined by electrical conductivity, dynamic light scattering (DLS), small angle X-ray scattering (SAXS) and linear voltammetry. When different short-chain alcohols were employed as co-surfactants, together with sodium dodecyl sulfate (SDS) as surfactant, the DLS results indicated the systems to be monodisperse. Both the electrical conductivity of the MEs and the hydrodynamic radii of the droplets ( R H) increased with water content while R H diminished as temperature increased, no aggregation or percolation of the droplets being observed. In comparison to w/o MEs prepared with 3-methyl-1-butanol, those prepared with 1-pentanol presented higher electrical conductivity and larger limiting currents at a Pt ultramicroelectrode for oxidation of the water occluded into the particles. Finally, from the electrochemical viewpoint the use of 1-pentanol is recommended, no advantage being gained by using any of the other tested alcohols.
Keywords: Soybean oil; Microemulsion; Co-surfactant; 1-Pentanol; Light scattering; Voltammetry; Electrical conductivity; SAXS
V2O5 nanoparticles obtained from a synthetic bariandite-like vanadium oxide: Synthesis, characterization and electrochemical behavior in an ionic liquid
by Willian G. Menezes; Dayane M. Reis; Tânia M. Benedetti; Marcela M. Oliveira; Jaísa F. Soares; Roberto M. Torresi; Aldo J.G. Zarbin (pp. 586-593).
Stable and crystalline V2O5 nanoparticles (diameter of 15nm) have been prepared by thermal treatment of a layered vanadium oxide, V10O24·9H2O. An electrode built with these nanoparticles showed high electroactivity in an ionic liquid electrolyte.Highly stable and crystalline V2O5 nanoparticles with an average diameter of 15nm have been easily prepared by thermal treatment of a bariandite-like vanadium oxide, V10O24·9H2O. Their characterization was carried out by powder X-ray diffractometry (XRD), Fourier transform infrared (FT-IR) and Raman spectroscopies, and transmission electron microscopy (TEM). The fibrous and nanostructured film obtained by electrophoretic deposition of the V2O5 nanoparticles showed good electroactivity when submitted to cyclic voltammetry in an ionic liquid-based electrolyte. The use of this film for the preparation of a nanostructured electrode led to an improvement of about 50% in discharge capacity values when compared with similar electrodes obtained by casting of a V2O5 xerogel.
Keywords: V; 2; O; 5; nanoparticles; Bariandite; Ionic liquid; Electrophoretic deposition method (EPD); Li; +; -battery
A general, accurate procedure for calculating molecular interaction force
by Pinghai Yang; Xiaoping Qian (pp. 594-605).
NURBS based surface formulation for calculating van der Waals force: (a) NURBS representation of a sphere; (b) subdivided NURBS patches; (c) analytical solution and the numerical results; (d) relative error.The determination of molecular interaction forces, e.g., van der Waals force, between macroscopic bodies is of fundamental importance for understanding sintering, adhesion and fracture processes. In this paper, we develop an accurate, general procedure for van der Waals force calculation.This approach extends a surface formulation that converts a six-dimensional (6D) volume integral into a 4D surface integral for the force calculation. It uses non-uniform rational B-spline (NURBS) surfaces to represent object surfaces. Surface integrals are then done on the parametric domain of the NURBS surfaces. It has combined advantages of NURBS surface representation and surface formulation, including (1) molecular interactions between arbitrary-shaped objects can be represented and evaluated by the NURBS model further common geometries such as spheres, cones, planes can be represented exactly and interaction forces are thus calculated accurately; (2) calculation efficiency is improved by converting the volume integral to the surface integral.This approach is implemented and validated via its comparison with analytical solutions for simple geometries. Calculation of van der Waals force between complex geometries with surface roughness is also demonstrated. A tutorial on the NURBS approach is given in .
Keywords: van der Waals forces/energies; NURBS surface; Surface formulation
Formation conditions and stability of a toxic tridecameric Al polymer under a soil environment
by Akira Etou; Shuqin Bai; Tomoyuki Saito; Hiroaki Noma; Yoshihiro Okaue; Takushi Yokoyama (pp. 606-609).
27Al MAS NMR spectrum for Al13 adsorbed on chelex 100. This spectrum suggests that Al13 can be stably adsorbed onto the surface of microbes by weak electrostatic interaction between negative charges (–CH2COO−) and positive charges ([Al13]7+) without decomposition.It is important to study the formation conditions and the stability of the tridecameric Al polymer (Keggin-type Al13 polycation, [AlO4Al12(OH)24(H2O)12]7+, known as Al13) due to its strong toxicity to living organisms of a soil environment. In order to examine the pH range where toxic Al13 can exist in aqueous solution,27Al NMR spectra for sample solutions containing Al3+ ions with various pH (pH 3.5–6.1) were measured. The results show that the peak due to Al13 (peak due to 4-coordinated Al around 63ppm) appeared at pH 3.6–5.7 and the peak intensity was relatively high at pH 4.1–4.8, suggesting that Al13 can be formed at pH 3.6–5.7, while it can exist dominantly at pH 4.1–4.8. It was also found that Al13 can stably adsorb onto a chelate resin, Chelex 100, by weak electrostatic interaction. The Chelex 100, with iminodiacetate groups, served as a model compound for surfaces of microbes covered with carboxyl groups and for surfaces of soil particles covered with humic substances having many carboxyl groups. Additionally, decomposition of Al13 did not occur even after adsorption, and its pH stability range was wide compared to that in aqueous solution.
Keywords: Al; 13; Formation condition; Stability; Surfaces of microbes and soil particles; 27; Al NMR
Synthesising gold nanoparticles within bola fatty acid nanosomes
by Jean-Paul Douliez; Bruno Novales; Cédric Gaillard (pp. 610-613).
We report on the synthesis of 1 to 10nm gold nanoparticles (AuNP ) stabilized by bola fatty acid nanosomes in water. Those nanoparticles could be phase transferred to dichloromethane by rendering the surface of the nanosomes more hydrophobic.We report on the synthesis of gold nanoparticles (Au-NP) stabilized by a layer of mercapto and/or hydroxyl bola palmitic acid–tetrabutyl ammonium salts (TBAOH) which form nanosomes in water. Mixing both bola fatty acids in water in various proportions allowed to tune the nanoparticle diameter from 1 to 10nm using NaBH4 as a reductor. Those nanoparticles could be phase transferred to dichloromethane by adding a more hydrophobic counter-ion than TBAOH, its derivative with octyl chains (TOAOH). Finally, we used those Au-NP to formulate emulsions, the stability of which was followed as a function of particle size and time. The emulsions were stable but creamed after several hours. We conclude that bola fatty acid nanosomes are then good candidates to synthesize gold nanoparticles dispersed either in water, organic solvents and emulsions.
Keywords: Gold nanoparticles; Nanosomes; Self-assembly; Fatty acid
Sulfonation of ordered mesoporous carbon supported Pd catalysts for formic acid electrooxidation
by Zhi-Peng Sun; Xiao-Gang Zhang; Hao Tong; Yan-Yu Liang; Hu-Lin Li (pp. 614-618).
A novel supporting material containing benzenesulfonic acid groups and ordered mesoporous carbons (OMCs) was first prepared, which was beneficial for promoting the catalytic activity of Pd/f-OMCs for formic acid oxidation.A novel supporting material containing benzenesulfonic acid (BSA) groups and ordered mesoporous carbons (OMCs) was first prepared by in situ radical polymerization of 4-styrenesulfonate and isoamyl nitrite under ambient conditions. Then, Pd nanoparticles were deposited on as-produced OMCs (f-OMCs) by theNaBH4 reduction method. The structure and nature of the resulting composites were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and nitrogen adsorption–desorption. The results show that BSA groups are created and the texture and surface chemistry are altered, whereas the ordered porous structure is maintained. The electrocatalytic properties of the Pd/f-OMCs catalysts for formic acid oxidation (HCOOH) have been investigated by cyclic voltammetry and chronoamperometry methods, and excellent electrocatalytic activity can be observed.
Keywords: Sulfonation; OMCs; Pd nanoparticles; HCOOH; Electrooxidation
Impact of fluid memory on wetting approaching the air entrainment limit
by Y. Wei; S. Garoff; L.M. Walker (pp. 619-621).
Shadow of a dynamic meniscus of a Boger fluid forced into a liquid bath near air entrainment.The high shear rates innate to the flow fields near a moving contact line suggest that non-Newtonian behavior in a fluid should impact its dynamic wetting behavior. We compare the dynamic wetting behavior of an elastic Boger fluid with its Newtonian base fluid to probe the impact of slow (on the order of seconds) relaxation modes on dynamic wetting as the air entrainment limit is approached and the Weissenberg number is of order one.
Keywords: Non-Newtonian; Wetting; Dynamic contact angle; Spreading; Boger fluid; Elastic fluid
by Arthur Hubbard (pp. 622-622).