Journal of Colloid And Interface Science (v.348, #2)
Mo6S3I6–Au composites: Synthesis, conductance, and applications
by Renyun Zhang; Magnus Hummelgård; Damjan Dvorsek; Dragan Mihailovic; Håkan Olin (pp. 299-302).
Mo6S3I6–Au nanocomposites were synthesized with tunable gold nanoparticle sizes and densities with a one-step method, leading to different electric properties. DNA-mediated conductance changes of Mo6S3I6–Au networks suggest the application of Mo6S3I6–Au nanocomposites in biosensing.A single-step, premixing method was used to directly deposit gold nanoparticles on Mo6S3I6 (MSI) molecular wire bundles. Gold nanoparticles with different sizes and densities were coated on the MSI by changing the concentration of the gold containing salt, HAuCl4. TEM, SEM, and EDX characterization showed deposition of gold nanoparticles on the MSI nanowire surface. The electrical resistance of these MSI–Au composites was more than 100 times lower than that for pure MSI, and was mainly dependent on the density of the deposited gold nanoparticles. Furthermore, we immobilized thiol group-labeled oligonucleotide on the composites and then hybridized with a fully matched sequence. The resistance of the MSI–Au composites increased during the thiol step, while it decreased by hybridizing, due to the conductance difference between single- and double-stranded DNA chains. These results indicate that this new kind of MSI–Au composite could be used as a platform for different applications, including biosensors.
Keywords: Mo; 6; S; 3; I; 6; nanowire; Gold nanoparticles; Nanocomposites; Synthesis; DNA sensing
Ultralong Cu(OH)2 and CuO nanowire bundles: PEG200-directed crystal growth for enhanced photocatalytic performance
by Yu Li; Xiao-Yu Yang; Joanna Rooke; Guastaaf Van Tendeloo; Bao-Lian Su (pp. 303-312).
Variations in nanostructure morphology can give rise to different photocatalytic activities. Oriented nanowires containing a high number of photocatalytically active sites can be selectively synthesized by the addition of structure-directing agents, which affect photocatalytic performance.Ultralong Cu(OH)2 and CuO nanowire bundles with lengths ranging from tens to hundreds of micrometers have been selectively synthesized on a large scale by a facile solution-phase method, using PEG200 as growth-directing agent. The growth mechanisms were investigated by monitoring the nanowire evolution process. The results showed that under the action of PEG200 molecules, the Cu(OH)2 and CuO nanowires were first formed through oriented attachment of colloidal particles, then through side self-assembly leading to nanowire bundles, and finally to CuO nanoleaves. PEG200 plays a critical role in the synthesis of nanowires as it not only prevents the random aggregation of colloidal particles toward CuO nanoleaves but also helps to orientate nanowire growth by the coalescence and alignment in one direction of the colloidal particles. The concentration of OH− in the reaction system is also important for nanowire growth. In the absence of PEG200, nanoleaves are formed by an Ostwald ripening process. The band-gap value estimated from a UV–Vis absorption spectrum of CuO nanowire bundles is 2.32eV. The photodegradation of a model pollutant, rhodamine B, by CuO nanowires and nanoleaves was compared with commercial nanopowders, showing that the as-synthesized ultralong CuO polycrystalline nanowire bundles have an enhanced photocatalytic activity with 87% decomposition of rhodamine B after an 8-h reaction, which was much higher than that of single-crystal nanoleaves (61%) and commercial nanopowders (32%). The origin of the high photocatalytic activity of these new polycrystalline CuO nanowire bundles has been discussed. This present work reveals that the (002) crystallographic surface is more favorable for photocatalytic decomposition of organic compounds and that these ultralong CuO nanowire bundles are potential candidates for photocatalysts in wastewater treatment.
Keywords: Ultralong; Copper oxide colloidal particles; Nanowire bundles; Photocatalyst; Poly(ethylene glycol); Oriented attachment mechanism; Side self-assembly; Ostwald mechanism
Increasing particle size of a synthetic smectite for polymer nanocomposites using a supercritical hydrothermal treatment
by Ryo Ishii; Nobuyuki Teshima; Takeo Ebina; Fujio Mizukami (pp. 313-321).
A supercritical hydrothermal treatment of a synthetic smectite, stevensite, brings about an increase in the particle size, leading to an improvement in the gas-barrier properties of the corresponding nanocomposite films with carboxymethylcellulose sodium salt (CMC Na).We have studied the effect of a supercritical hydrothermal process on the structural and surface morphological properties of synthetic smectite clay, stevensite (ST), in terms of the particle size, in order to enhance the functionality of the synthetic smectites as an inorganic filler for transparent clay/polymer nanocomposites. The ST aqueous suspensions were treated in a flow reactor system at 673K and 25MPa. The structural characterizations revealed that the ST retained a layered structure composed of polymeric sheets of SiO4 tetrahedra after the treatment. The treated ST possessed a particle size of 71nm, approximately twice that of the original ST (36nm) for the 0.1wt.% suspension using an operation condition at a flow rate of 0.085gs−1. SEM observation revealed that an enlarged particle was formed from cohesive aggregates, suggesting that the increase in size of the particles was caused by the cohesion of the microcrystallites or primary particles of ST. The treated ST was subsequently used to prepare nanocomposites with carboxymethylcellulose sodium salt (CMC Na) to evaluate the effect of the supercritical treatment. The treated ST nanocomposite films retained their transparency which is very similar to the original ST nanocomposite films. Furthermore, the nanocomposite films, which had a high CMC Na ratio ranging from 40 to 90wt.%, showed improved oxygen barrier properties when compared with those of original ST. The tortuous model revealed that this improvement was mainly due to the increase of the particle size. Consequently, the supercritical treatment successfully brought about the growth of the ST particles, leading to the development of functional synthetic clays for clay/polymer nanocomposites.
Keywords: Clay; Particle growth; Nanocomposite; Gas-barrier properties; Supercritical treatment; Stevensite
Plasma functionalization of AFM tips for measurement of chemical interactions
by Cedric Volcke; Ram Prasad Gandhiraman; Vladimir Gubala; Colin Doyle; G. Fonder; Paul A. Thiry; Attilio A. Cafolla; Bryony James; David E. Williams (pp. 322-328).
Chemical force titration experiments as a confirmation of successful functionalization and stability of PECVD-deposited APTES coatings on AFM probes.In this paper, a new, fast, reproducible technique for atomic force microscopy (AFM) tips functionalization used for chemical interaction measurements is described. Precisely, the deposition of an aminated precursor is performed through plasma-enhanced chemical vapor deposition (PECVD) in order to create amine functional groups on the AFM tip and cantilever. The advantages of the precursor, aminopropyltriethoxysilane (APTES), were recently demonstrated for amine layer formation through PECVD deposition on polymeric surfaces. We extended this procedure to functionalize AFM probes. Titration force spectroscopy highlights the successful functionalization of AFM tips as well as their stability and use under different environmental conditions.
Keywords: Force spectroscopy; Amine; PECVD; Titration force spectroscopy
Stresses exerted by ZnO, CeO2 and anatase TiO2 nanoparticles on the Nitrosomonas europaea
by Xiaohua Fang; Ran Yu; Bingquan Li; Ponisseril Somasundaran; Kartik Chandran (pp. 329-334).
N. europaea cells grown in media containing (a) control (no anatase TiO2 nanoparticles (NPs)), (b) 20ppm of 25nm anatase TiO2 NPs (c)200ppm of 25nm anatase TiO2 NPs, (d) 200ppm of 200nm anatase TiO2 NPs, (e) 20ppm of ZnO NPs, (f) 20ppm CeO2 NPs for 4h.Recent studies have shown that nano-bio interfaces are the most complex and the least understood. Notably, nanotoxicity of these nanoparticles is not even well recognized. In this work, we examined the toxic effects of different nanoparticles on bacteria cells ( Nitrosomonas europaea). The four nanoparticles involved are: 25nm anatase TiO2, 200nm anatase TiO2, ZnO and CeO2 particles. These particles will have different electrical charges in the cell cultivating media. It has been observed that even with only 4h of dosing, all of the particles caused apparent morphological damage to the cells. Experimental results suggest that ZnO particles exert the stress on cells by its dissolution and releasing of Zn2+ ions. The TEM and AUC (analytical ultracentrifuge) result suggest that cells become heavier in presence of CeO2 and TiO2 particles. No visible clear intrusions of bulk nanoparticles were observed. However, both the analytical ultracentrifuge and TEM results show that cells are heavier when being damaged.
Keywords: Nanoparticles; Bacteria
Catalytic gold nanoparticle driven pH specific chemical locomotion
by Krishna Kanti Dey; Biswa Ranjan Panda; Anumita Paul; Saurabh Basu; Arun Chattopadhyay (pp. 335-341).
Au NPs deposited on polymer resin beads catalyzed the decomposition of alkaline H2O2 and helped in propelling the beads upward with velocities that depended on the pH of the solution.Gold nanoparticle (Au NP) catalyzed decomposition of alkaline hydrogen peroxide has been utilized in driving chemical locomotives in a liquid. Au NPs deposited on spherical micron sized polymer resin beads catalyzed the decomposition of H2O2 in the pH range 9.1–10.8. The O2 gas bubbles produced in the decomposition moved the beads upward with average velocities that depended on the pH of the solution. The measured average velocity of the bead increased with the increase in pH in the range 9.1–10.8. Above this pH, the self-decomposition of H2O2 produced sufficient bubbles in the medium that made the motion haphazard and thus prevented a clear measurement of the velocity. The observed accelerated motion of the locomotive has been explained by considering the time-dependent growth of O2 gas bubbles on the polymer, while taking into consideration desorption and other factors.
Keywords: H; 2; O; 2; decomposition; Catalytic motors; Autonomous transport; pH; Nanoparticle
Effect of the agglomeration of TiO2 nanoparticles on their photocatalytic performance in the aqueous phase
by Gang Li; Lu Lv; Haitao Fan; Junyan Ma; Yanqiang Li; Yong Wan; X.S. Zhao (pp. 342-347).
Schematic representation of the dispersion of TiO2 nanoparticles under various conditions.TiO2 nanoparticles have been widely explored as photocatalysts in the degradation of organic matters present in water. However, spontaneous agglomeration of TiO2 nanoparticles in a suspension is a crucial issue that must be addressed before the photocatalyst can be used for water treatment. In the present work, the nature of the agglomeration of TiO2 nanoparticles in aqueous suspension was investigated. Two approaches to minimize the agglomeration of colloidal TiO2 particles were investigated. A careful control over the pH of the system was found to be an effective method for stabilizing colloidal TiO2 particles and to significantly enhance the adsorption of orange II. As a result, the overall photocatalytic degradation rate was greatly accelerated. In addition to pH control, modification of TiO2 particles using polyelectrolyte poly allylamine hydrochloride (PAH) was observed to be an effective approach for preventing colloidal TiO2 particles from agglomeration.
Keywords: Colloidal TiO; 2; Agglomeration; Photocatalysis; Zeta potential
The effect of ionic strength on the electrophoretic mobility and protonation constants of an EPS-producing bacterial strain
by Janette Tourney; Bryne T. Ngwenya (pp. 348-354).
The presence of an EPS layer was found to affect the electrophoretic mobility of a bacterial strain across an ionic strength range, but not the protonation constants.The production of extracellular polymeric substances (EPS) by bacteria significantly alters the physical structure of the cell wall-solution interface, potentially affecting cell surface reactivity and colloidal (transport) properties of the cells. This study investigated the effect of the EPS layer on the electrostatic properties of the cell surface by conducting electrophoretic mobility (EM) analysis and potentiometric titrations at ionic strengths of 0.001M, 0.01M and 0.1M, using both native cells, with the EPS-layer intact, and EPS-free cells of the gram-positive thermophile, Bacillus licheniformis S-86. Electrophoretic mobility measurements indicated that the isoelectric point for both cell types was below pH 2. At low ionic strength (0.001M), expansion of the EPS layer causes the EM of the native cells to have a smaller magnitude than that of the EPS-free cells. As ionic strength increases, this effect diminishes and at 0.1M the native cells have a higher EM than the EPS-free cells, which indicates that there is a relatively high charge density in the EPS layer.Higher total site concentrations obtained using potentiometric titration data modelling for the native cells are in agreement with the electrophoretic mobility data, and indicate a higher proton-active site density in the EPS layer compared to the EPS-free cell wall. The results of data modelling for titrations conducted at all three ionic strength values showed that there are no systematic changes in deprotonation constants or site concentrations as a function of ionic strength, indicating that the use of a non-electrostatic model is justified for this EPS-producing bacterial strain.
Keywords: Bacteria; EPS; Titrations; Electrophoretic mobility
Delamination of kaolinite–potassium acetate intercalates by ball-milling
by Hongfei Cheng; Qinfu Liu; Jinshan Zhang; Jing Yang; Ray L. Frost (pp. 355-359).
SEM image of delaminated kaolinite through ball-mill after intercalation.Structural changes in intercalated kaolinite after wet ball-milling were examined by scanning electron microscopy (SEM), X-ray diffraction (XRD), specific surface area (SSA) and Fourier transform infrared spectroscopy (FT-IR). The X-ray diffraction pattern at room temperature indicated that the intercalation of potassium acetate into kaolinite caused an increase of the basal spacing from 0.718 to 1.42nm, and with the particle size reduction. The surface area increased sharply with the intercalation and delamination by ball-milling. The wet ball-milling kaolinite after intercalation did not change the structural order, and the particulates have high aspect ratio according SEM images.
Keywords: Kaolinite; Potassium acetate; Intercalation; Delamination; Particle size
Folate mediated in vitro targeting of depolymerised trimethylated chitosan having arginine functionality
by Viola B. Morris; Chandra P. Sharma (pp. 360-368).
Folic acid conjugated low molecular weighed trimethylated chitosan having arginine functionality formed core–shell nano-structured particles with DNA displayed blood compatibility, cellular and nuclear uptake at cancer cell line having folate receptor.Delivery vectors having targeting ligands provide an impending impact on cancer gene therapy. Our work focuses on folate mediated targeting induced by conjugating poly(ethylene glycol)–folate (PEG–FA) with arginine modified chitosan polymer having low molecular weight of 15kDa and high degree of quaternization (ATFP15H). The ATFP15H derivative on condensation with plasmid DNA formed nanoparticles with core shell nanostructure. It also affirmed good buffering capacity. The derivative was found to protect DNA from DNase I degradation and also from disassembly in presence of negatively charged plasma proteins. It exhibited blood compatibility in terms of percentage hemolysis, erythrocyte aggregation and also by platelet activation. At a concentration of 10μg, the capability of the derivative to enhance cell growth at normal cell growing conditions was observed. The transfection efficiency was also found to be comparable to PEI when transfected in KB cell line, which over expressed the folate receptor (FR) in presence of 10% fetal bovine serum (FBS). On comparison with native chitosan and trimethylated chitosan, ATFP15H derivative exhibited high cellular uptake and nuclear localization due to the superior colloidal stability attained on conjugation with polyethylene glycol. This has been ascertained by flow cytometry and YOYO labeling of plasmid DNA.
Keywords: Trimethylated chitosan; Arginine; Gene delivery; TEM; Folate receptor targeting; Colloidal stability; Reentrant condensation
Facile synthesis of high-quality water-soluble N-acetyl-l-cysteine-capped Zn1− xCd xSe/ZnS core/shell quantum dots emitting in the violet–green spectral range
by Jie Cao; Bing Xue; Hui Li; Dawei Deng; Yueqing Gu (pp. 369-376).
Zn1− xCd xSe and Zn1− xCd xSe/ZnS core/shell quantum dots (QDs) emitting in the violet–green spectral range have been synthesized successfully in aqueous solutions, using N-acetyl-l-cysteine (NAC) as a stabilizer.In this paper, we report a new facile method to synthesize water-soluble Zn1− xCd xSe and core/shell Zn1− xCd xSe/ZnS quantum dots (QDs) emitting in the violet–green spectral range, using N-acetyl-l-cysteine (NAC) as a stabilizer. The influence of various experimental variables, including the precursor Zn/Cd/Se/NAC molar ratios, the pH of original solution and the refluxing time on optical properties were explored systematically. The obtained aqueous Zn1− xCd xSe QDs exhibit a tunable photoluminescence (PL) emission (from ∼415nm to 506nm) and a favorable narrow PL bandwidth (FWHM: 27–38nm). After coating with a ZnS shell, the PL emission intensity of the formed core/shell Zn1− xCd xSe/ZnS QDs is greatly increased (PL quantum yield (QY): ∼30%). These resulting Zn1− xCd xSe and core/shell Zn1− xCd xSe/ZnS QDs were further characterized by transmission electron microscopy (TEM), energy disperse spectroscopy (EDS) and X-ray diffraction (XRD). In addition, the cytotoxicity and the fluorescence imaging of Zn1− xCd xSe/ZnS QDs to MCF-7 cells were preliminarily investigated. The experimental results show that the as-prepared violet–green-emitting Zn1− xCd xSe/ZnS QDs have low cytotoxicity, which makes them an ideal inorganic fluorescent probe for biolabeling and cell imaging.
Keywords: N; -acetyl-; l; -cysteine; Zn; 1−; x; Cd; x; Se/ZnS; Quantum dots; Water-soluble; Violet–green-emitting
Covalent synthesis of organophilic chemically functionalized graphene sheets
by Jianfeng Shen; Na Li; Min Shi; Yizhe Hu; Mingxin Ye (pp. 377-383).
Organophilic chemically functionalized graphene was prepared by reacting 1-bromobutane with graphene oxide and the resulting homogeneous organic media exhibits long-term stability.In this study, we report a scalable, fast, and easy method for preparation of organophilic chemically functionalized graphene (OCFG) sheets. The basic strategy involved the preparation of graphite oxide (GO) and the complete exfoliation of GO into graphene oxide sheets, followed by reacting with 1-bromobutane to obtain OCFG sheets. Thermogravimetric analysis, Raman spectroscopy, and Fourier transform infrared spectroscopy indicated the functionalization of GO. Transmission electron microscopy and atomic force microscopy were used to demonstrate the structure of produced graphene oxide and OCFG sheets. Ultraviolet–visible spectroscopy confirmed that OCFG sheets disperse well in organic solvents and the solutions obey Beer’s law. The resulting organic dispersions are homogeneous, exhibit long-term stability, and are made up of graphene sheets a few hundred nanometers large. The ability to prepare graphene dispersions in organic media facilitates their combination with polymers to yield homogeneous composites.
Keywords: Graphene; Organophilic; Stability; Processability
A coagulation technique for purification of graphene sheets with graphene–reinforced PVA hydrogel as byproduct
by Vadahanambi Sridhar; Il-Kwon Oh (pp. 384-387).
PVA mediated coagulation process for purification of graphene.A simple and rapid coagulation method to separate graphene from partially or incompletely reduced graphene oxide is developed in this study. Our isolation technique is not only simple and effective but also can be applied to a quality control in graphene production. Interestingly, the byproduct of our technique is valuable graphene–reinforced PVA hydrogel.
Keywords: Graphene; Purification; Coagulation; PVA hydrogels
Insertion of semifluorinated diblocks on DMPC and DPPC liposomes. Influence on the gel and liquid states of the bilayer
by Juan Sabín; Gerardo Prieto; Joan Estelrich; Félix Sarmiento; Miguel Costas (pp. 388-392).
Schematic representations of the configuration of liposomes formed by DPPC and F6H16 at 1:2 lipid/F nH m molar ratio.Differential Scanning Calorimetry (DSC) was used to study the effect of the incorporation of a series of semifluorinated diblocks F nH m (F6H10, F6H16, F8H14, F8H16, F8H18 and F8H20) on the gel and liquid states of the bilayer of large multilamellar DMPC and DPPC liposomes. The presence of the F nH m diblocks affects slightly theT m of the main gel–liquid transitions of DMPC and DPPC, but is accompanied by the appearance of a second transition in the calorimetric traces whoseT m is mainly determined by the length of the F n segment. The DSC results are consistent with the previously established conclusion that the F n segments of the diblocks form a central layer in the core of the lipid bilayer, with the H m segments being interdigitated with the lipid chains. The DSC traces suggest that the structure of the fluorinated liposomes is a double bilayer at 3:4 and 1:2 and a trilayer at 2:1 lipid/F nH m molar ratios. At temperatures between the two phase transitionsT m’s, the fluorinated liposomes are neither in a gel-like or a liquid-like state but rather posses both characteristics.
Keywords: Fluorinated liposomes; F; n; H; m; DSC; Phase transitions; Double bilayer; Trilayer
A two-dimensional magnetic hybrid material based on intercalation of a cationic Prussian blue analog in montmorillonite nanoclay
by Dimitrios Gournis; Christina Papachristodoulou; Enrico Maccallini; Petra Rudolf; Michael A. Karakassides; Dimitrios T. Karamanis; Marie-Hélène Sage; Thomas T.M. Palstra; Jean-François Colomer; Konstantinos D. Papavasileiou; Vasilios S. Melissas; Nicolaos H. Gangas (pp. 393-401).
Intercalation of a new cationic ferric ferrocyanide in the interlayer space of a cation-adsorbing nanoclay enabled the synthesis of a highly ordered two-dimensional hybrid magnetic material.A highly ordered two-dimensional hybrid magnetic nanocomposite has been prepared by synthesizing and intercalating a new cationic aluminum-hydroxy ferric ferrocyanide compound into a cation-adsorbing nanoclay (montmorillonite). Chemical and structural properties were investigated by X-ray diffraction, transmission electron microscopy, thermogravimetric and differential thermal analyses, Fourier transform infrared, X-ray photoemission, and Mössbauer spectroscopies. Elemental analysis was based on proton-induced gamma ray emission and X-ray fluorescence spectroscopy data, N/C elemental ratios, and cation-exchange capacity measurements. Magnetic properties were studied by SQUID magnetometry. The results suggest: (i) that the cationic Prussian blue analog comprises Al-hydroxy cations embedded into a monolayer thick two-dimensional ferric ferrocyanide array; and (ii) that the clay-Prussian blue nanohybrid consists of such arrays stacked between the clay layers. The latter material orders ferromagnetically at ∼5K showing a hundred times higher remanence than that of the starting material, soluble Prussian blue (ammonium ferric ferrocyanide).
Keywords: Prussian blue; Ferric ferrocyanide; Cationic complex; Montmorillonite; Clay intercalation; Two-dimensional hybrid materials
Electrical potentials of two identical planar, cylindrical, and spherical colloidal particles in a salt-free medium
by Jyh-Ping Hsu; Chih-Hua Huang (pp. 402-407).
Electrical distribution for the case of two charged particles in a salt-free medium.A perturbation solution based on the curvature of the surface of a particle is derived for the electrical potential of two planar, cylindrical, and spherical colloidal particles immersed in a salt-free medium. Compared with the available results in the literature, the present approach improves both the accuracy and the applicable range in the level of the surface potential, the valence of counterions, and the thickness of the double-layer surrounding a particle. The zero-order perturbation solution is exact for the case of two planar particles. Under typical conditions, the averaged percentage deviation of the first-order perturbation solution is on the order of ca. 5% for both two cylindrical and two spherical particles.
Keywords: Electrical potential; Two planar, cylindrical, and spherical particles; Salt-free medium; Perturbation solution
Microgel–silica hybrid particles: Strategies for tunable nanostructure, composition, surface property and porphyrin functionalization
by Xiaoqing Li; Jianjun Yuan; Huan Liu; Lei Jiang; Shuqing Sun; Shiyuan Cheng (pp. 408-415).
Fluorescent microgel–silica hybrid particles with tunable porous nanostructure, composition and surface property were synthesized by using copolymer microgels as colloidal templates for silicification reaction under ambient conditions.Cationic poly(acrylamide- co-2-(dimethylamino) ethyl methacrylate, methyl chloride quaternized) (poly(AM- co-DMC)) microgels with various cross-linking degrees and compositions were synthesized and used as colloidal templates for controlled formation of microgel–silica hybrid particles at ambient conditions. The combined studies from transmission electron microscopy, solid-state29Si magic angle spinning NMR spectroscopy, thermogravimetry and aqueous electrophoresis indicated that the porous nanostructure, composition and surface zeta potentials of microgel–silica hybrid particles could be well controlled by simply adjusting the silicification reaction times, cross-linking degrees and compositions of microgels and media composition for silica deposition. Comparative studies from thermogravimetry and X-ray photoelectron spectroscopy on the compositions of microgel–silica particles prepared from different silica deposition times indicated that organic–inorganic composition distribution of hybrid particles is not uniform for whole particles, with silica-rich core and copolymer-rich shell. Furthermore, we demonstrated the facile incorporation of tetra(4-sulfonatophenyl)porphine (TSPP) molecules into microgel–silica particles, leading to the biomimetic formation of porous hybrid particles with bright fluorescent emission features. We expect that these well controlled and functionalized hybrid particles have potential applications for encapsulation, controlled release, labeling or imaging.
Keywords: Microgel; Nanostructured hybrid particles; Silica; Porphyrin
Spatial control of dewetting: Highly ordered Teflon nanospheres
by Hyungmin Park; Thomas P. Russell; Soojin Park (pp. 416-423).
We demonstrate a simple route for fabricating highly ordered Teflon nanospheres by guiding with saw-toothed patterns. The contact of Teflon and PDMS induced dewetting of the film with high degree of order.We demonstrate a simple route for fabricating Teflon nanospheres with high degree of order by guiding with saw-toothed patterns having different pitches and amplitudes. Teflon precursor solutions were spin-coated onto substrates with different surface energies. Immediately after spin-coating, a saw-toothed patterned surface was brought into contact with the precursor film at 120°C for 1min to induce dewetting of the film but in the confined geometry defined by the saw-tooth pattern. Depending on the pitches and amplitudes of saw-toothed patterns, arrays of highly ordered nanospheres having a range of sizes and separation distances were obtained. And also sizes of Teflon droplets can be tuned by changing the thickness of Teflon film. Hydrophobic nanostructured Teflon patterns can be used as masters for fabricating polymeric replica and as hydrophobic surfaces.
Keywords: Teflon nanosphere; Saw-toothed pattern; Teflon precursor
Self-assembled nanoparticles of functional copolymers for photonic applications
by Iole Venditti; Ilaria Fratoddi; Christian Palazzesi; Paolo Prosposito; Mauro Casalboni; Cesare Cametti; Chiara Battocchio; Giovanni Polzonetti; Maria Vittoria Russo (pp. 424-430).
Emulsion copolymerization of phenylacetylene (PA) with acrylic acid (AA) or N,N-dimethylpropargylamine (DMPA) produces functionalized nanoparticles (diameters 80–500nm) with superficial charge density and three-dimensional photonic crystals property.A modified emulsion copolymerization of phenylacetylene (PA) with hydrophilic monomers having different functions, i.e., acrylic acid (AA) and N,N-dimethylpropargylamine (DMPA) respectively, yields functionalized polymeric P(PA-co-AA) and P(PA-co-DMPA) nanoparticles. The systematic investigation on the experimental parameters affecting size, surface charge and polydispersity of the copolymers (initiator concentration, reaction time, cosolvent and PA/comonomer ratios) allows to modulate the nanoparticle physico-chemical properties. Spherical shaped particles with diameters in the range 80–500nm, low polydispersity (PI values in the range 1.11–1.30) and different surface charge densities, between 0.44 and 2.87μC/cm2, have been consistently obtained and characterized by means of Dynamic Light Scattering (DLS), laser Doppler electrophoretic and Scanning Electron Microscopy (SEM) studies. XPS measurements have provided information on the nanoparticles chemical surface structure and suggest that AA and DMPA units are preferentially distributed on the surface of the spheres. The nanospheres self-assemble giving large domains (9.5×14.5μm). Photonic analysis of the self-assembled copolymeric nanoparticles has been performed by means of Spectroscopic Ellipsometry (SE) and Bragg reflection spectroscopy, both of them demonstrating a three-dimensional photonic crystal property of these systems.
Keywords: Functional copolymers; Nanoparticles; ζ; -Potential; XPS; Polyphenylacetylene; Photonic crystals
Facile synthesis of monodisperse polymer/SiO2/polymer/TiO2 tetra-layer microspheres and the corresponding double-walled hollow SiO2/TiO2 microspheres
by Han Zhang; Xu Zhang; Xinlin Yang (pp. 431-440).
Monodisperse P(EGDMA- co-MAA)/SiO2/P(EGDMA- co-MAA)/TiO2 tetra-layer microspheres and the corresponding hollow SiO2/TiO2 double-walled microspheres were synthesized by the combination of distillation precipitation polymerization and controlled sol–gel process and further calcination in air.Monodisperse tetra-layer poly(ethyleneglycol dimethacrylate- co-methacrylic acid) (P(EGDMA- co-MAA))/SiO2/P(EGDMA- co-MAA)/TiO2 tetra-layer microspheres were facilely synthesized by the combination of the distillation precipitation polymerization for the preparation of P(EGDMA- co-MAA) layers and the controlled sol–gel hydrolysis of inorganic precursors for the formation of silica (SiO2) and titania (TiO2) layers. The thickness of the outer titania shell-layer was well-controlled via altering the feed of titanium tetrabutoxide (TBOT) during the sol–gel hydrolysis, while the size of polymeric layers were facilely controlled via a multi-step addition of ethyleneglycol dimethacrylate (EGDMA) crosslinker and methacrylic acid (MAA) monomer during the polymerization. The corresponding double-walled hollow inorganic microspheres containing SiO2 inner shell and TiO2 outer shell with various thickness were obtained after the selective removal of P(EGDMA- co-MAA) components via the calcination of the tetra-layer polymer/SiO2/polymer/TiO2 microspheres under 550°C for 4h in air. The structure and morphology of the resultant microspheres were characterized by transmission electron microscopy (TEM), X-ray diffractometer (XRD), X-ray photoelectron microscopy (XPS), and thermogravimetric analysis (TGA). Further, the photocatalytic properties of the resultant double-walled hollow SiO2/TiO2 microspheres were studied by photocatalytic degradation of methyl orange (MO) with ultraviolet (UV) irradiation of a 500W high-pressure mercury lamp.
Keywords: Tetra-layer inorganic/polymer microspheres; Double-walled hollow microspheres; Distillation precipitation polymerization; Photocatalyst
Electrode potential-dependent colorimetric response of fluorescein-modified layer-by-layer films in the presence of hydrogen peroxide
by Munenari Nagasaka; Kentaro Yoshida; Katsuhiko Sato; Tomonori Hoshi; Jun-ichi Anzai (pp. 441-445).
UV–visible absorption spectrum of fluorescein-containing LbL film depends on the electric potential applied in the presence of H2O2.Layer-by-layer (LbL) thin films composed of fluorescein-modified poly(allylamine) (F-PAH) and poly(styrenesulfonic acid) (PSS) were prepared on the surface of an indium–tin oxide (ITO) electrode and the electrode potential-dependent colorimetric response of the LbL films was studied in the presence of hydrogen peroxide (H2O2). The LbL films were prepared by an alternate deposition of F-PAH and PSS on the surface through an electrostatic force of attraction. The LbL films exhibited a UV–visible absorption band around 500nm originating from fluorescein residues in the film and the intensity of the absorption band depended on the pH of the solution to which the LbL film is exposed. The absorbance of the film was higher at neutral pH than that in weakly acidic solutions. The intensity of the absorption band decreased when an electrode potential higher than 0.6V was applied in the presence of H2O2, while virtually no response was observed at lower electrode potential. The colorimetric response was suppressed in solutions with higher buffer capacity. The results were rationalized on the basis of the changes in local pH at the vicinity of the electrode surface, which in turn was induced by electrolysis of H2O2 on the electrode surface. A possible application of the system for colorimetric sensing of H2O2 was discussed.
Keywords: Layer-by-layer film; Colorimetric response; Electrode potential; Fluorescein; Hydrogen peroxide
Lamellar self-assembly of a porphyrin derivative possessing poly(ethylene oxide) methyl ether and the formation of a silica–porphyrin hybrid with tetraethoxysilane
by Shintaro Nasu; Kazuyuki Kuroda (pp. 446-451).
A lamellar structured thin film and a mesostructured porphyrin-silica hybrid film were prepared by the self-assembly of a porphyrin derivative possessing poly(ethylene oxide) methyl ether.A porphyrin derivative, possessing poly(ethylene oxide) methyl ether on the para positions of phenyl groups in the tetraphenylporphyrin, is self-assembled to form a thin film with a lamellar structure. A split of the absorption band in the visible light region of the film strongly indicates the stacking of the porphyrin rings in the film. A molecular periodicity perpendicular to the substrate, proven by in-plane XRD, suggests the perpendicular orientation of the porphyrin rings. A silica–porphyrin hybrid film with a mesostructure was prepared from the mixture of the derivative and tetraethoxysilane. The mesoscale periodicity of the hybrid was confirmed by low-angle XRD and TEM data. The presence of the grafted groups suppressed the segregation of tetraphenylporphyrin rings in the formation of the hybrids, which is in clear contrast to the separated precipitation of tetraphenylporphyrin from a mixture of underivatized tetraphenylporphyrin and hydrolyzed tetraethoxysilane. These results indicate that porphyrin derivatives can be utilized as the organic components in silica–organic hybrids if they are appropriately derivatized.
Keywords: Organic–inorganic hybrid; Mesostructured material; Self-assembly; Silica; Porphyrin; Amphiphiles
Spin-probe ESR and molecular modeling studies on calcium carbonate dispersions in overbased detergent additives
by Luciano Montanari; Francesco Frigerio (pp. 452-459).
Surfactant architecture of overbased calcium carbonate detergents, used as detergent additives in lubricating oils, is investigated by using ESR in combination with stable free radical nitroxide spin-probes.Oil-soluble calcium carbonate colloids are used as detergent additives in lubricating oils. They are colloidal dispersions of calcium carbonate particles stabilized by different surfactants; in this study alkyl-aryl-sulfonates and sulfurized alkyl-phenates, widely used in the synthesis of these additives, are considered. The physical properties of surfactant layers surrounding the surfaces of calcium carbonate particles were analyzed by using some nitroxide spin-probes (stable free radicals) and observing the corresponding ESR spectra. The spin-probe molecules contain polar groups which tend to tether them to the carbonate particle polar surface. They can reach these surfaces only if the surfactant layers are not very compact, hence the relative amounts of spin-probe molecules accessing carbonate surfaces are an index of the compactness of surfactant core. ESR signals of spin-probe molecules dissolved in oil or “locked” near the carbonate surfaces are different because of the different molecular mobility. Through deconvolution of the ESR spectra, the fraction of spin-probes penetrating surfactant shells have been calculated, and differences were observed according to the surfactant molecular structures.Moreover, by using specially labeled spin-probes based on stearic acids, functionalized at different separations from the carboxylic acid group, it was possible to interrogate the molecular physical behavior of surfactant shells at different distances from carbonate surfaces.Molecular modeling was applied to generate some three-dimensional micellar models of the colloidal stabilizations of the stabilized carbonate particles with different molecular structures of the surfactant.The diffusion of spin-probe molecules into the surfactant shells were studied by applying a starting force to push the molecules towards the carbonate surfaces and then observing the ensuing behavior.The simulations are in accordance with the ESR data and show that the geometrical organization of the surfactants depends on their molecular structure.The compactness of surfactant shells influences the properties of overbased detergents, especially their stability, their interaction with other additives used in lubricating oil formulations and with the acids produced by the combustion of fuel.
Keywords: Detergents; Overbased calcium sulfonate; Carbonate micelles; Spin-probe; ESR; Molecular modeling; Forced diffusion; Molecular dynamics
Foamability of aqueous suspensions of fine graphite and quartz particles with a triblock copolymer
by Diana N.H. Tran; Catherine P. Whitby; Daniel Fornasiero; John Ralston (pp. 460-468).
Photograph of foam transition for a 33wt.% graphite suspension from stage one in the foam evolution-curve.The foamability of a triblock copolymer solution was strongly influenced by the presence of particles. The stability of the foam was evaluated by measuring the foam volume, the drainage of water and particles, and the bubble size as a function of time. The higher stability of foams produced with hydrophilic quartz particles, compared with hydrophobic graphite particles, was related to the presence of quartz aggregates in the lamellae and Plateau borders reducing water drainage, and therefore thin film rupture and bubble coalescence. The copolymer adsorbed slightly more on the hydrophobic graphite, causing the particles to disperse and drain, with the water out of the foam, whereas the hydrophilic quartz aggregated and remain in the lamellar and Plateau borders of the foam.
Keywords: Foamability; Triblock copolymer; Film drainage; Bubble coalescence; Kinetic adsorption
Carbon dioxide/water, water/carbon dioxide emulsions and double emulsions stabilized with a nonionic biocompatible surfactant
by Enza Torino; Ernesto Reverchon; Keith P. Johnston (pp. 469-478).
Image of extremely small primary W/C droplets on the order of 150nm observed in the miniemulsion size range. The primary droplets formed the clusters of a relatively low polydispersity.Whereas microemulsions and emulsions of water and carbon dioxide have been reported for various surfactants with fluorocarbon surfactants, relatively few studies have been successful in forming these emulsions with hydrocarbon surfactants. Stable CO2/water and water/CO2 emulsions with droplets smaller than 1μm were formed at high shear with the nonionic surfactant polysorbate 80 (Tween 80). In order to understand the emulsion phase behavior at high shear, low shear phase behavior experiments were performed at the same temperature and pressure. For pressures up to 250bar and temperatures of 25–60°C, C/W emulsions were formed for water concentrations as low as 10%, as the surfactant is highly hydrophilic with limited CO2-philicity. However, with added NaCl, the surfactant partitioned away from water toward CO2, and W/C emulsions were formed with droplet sizes from a few 100nm to a few μm in diameter, which were stable for at least 24h. In addition C/W/C double emulsions are reported for the first time, as well as W/C/W/C triple emulsions. The ability to form emulsions with environmentally benign solvents, CO2 and water, and biocompatible surfactants is desirable for green reaction and separation processes, as well as production of materials including pharmaceutical particles and composites.
Keywords: Supercritical fluids; Emulsions; Tween 80; Nonionic surfactant; CO; 2; -in-water; Water-in-CO; 2; Double emulsions
Analysis of dynamic surfactant mass transfer and its relationship to the transient stabilization of coalescing liquid–liquid dispersions
by B.A. Grimes; C.A. Dorao; S. Simon; E.L. Nordgård; J. Sjöblom (pp. 479-490).
This work considers the implications of dynamic transport and adsorption of surfactant molecules during the separation of liquid–liquid dispersions via coalescence.In this work, experiments describing the behavior of the separation of a model liquid–liquid dispersion with various concentrations of a synthetic surfactant are presented which indicate that there is a dynamic stabilization of initially unstable emulsions that occurs when the initial surfactant concentration approaches the concentration that provides stable emulsions. A simple model is presented to suggest the mechanism for the dynamic stabilization of these emulsion systems that considers the redistribution of surfactant into the continuous phase after a coalescence event at the emulsion-bulk dispersed phase interface and the dynamic mass transport of surfactant in the continuous phase of the emulsion. The results indicate that coalescence at the interface between the emulsion layer and the bulk dispersed phase creates a local region in the vicinity of this interface where the concentration of the surfactant is much higher than the bulk surfactant concentration which could lead to a locally, dynamically stabilized emulsion at this interface. The extent to which the local excess surfactant concentration reduces the coalescence rate depends strongly on the rate of coalescence at the dense packed layer-bulk dispersed phase interface relative to the rate of surfactant diffusion through the dense packed layer and, of course, on the surfactant adsorption constant, the maximum adsorbed surfactant concentration, and the surface to volume ratio of the dispersed phase. Furthermore, the results indicate that coalescence can also act to significantly increase the local concentration of an initially very dilute surfactant in the vicinity of the interface between the emulsion layer and the bulk dispersed phase interface.
Keywords: Liquid–liquid dispersions; Emulsions; Surfactants; Sedimentation; Creaming; Coalescence; Gravity separation
General rules for the scaling behavior of linear wormlike micelles formed in catanionic surfactant systems
by Haiming Fan; Yun Yan; Zichen Li; Yi Xu; Lingxiang Jiang; Limin Xu; Bo Zhang; Jianbin Huang (pp. 491-497).
Scaling exponents for catanionic wormlike micelle systems can agree with values derived from the Cates model as the mixing ratio shifts toward electroneutral.We report in this work on the scaling behavior of wormlike micelles formed in a series of mixed systems of oppositely charged surfactants, including sodium decanote (SD)/hexadecyltrimethylammonium bromide (CTAB), sodium laurate (SL)/hexadecyltrimethylammonium bromide, sodium didecaminocystine (SDDC)/hexadecyltrimethylammonium bromide, and sodium dilauraminocystine (SDLC)/hexadecyltrimethylammonium bromide. Steady and dynamic rheological measurements were performed to characterize these wormlike micelles. The scaling behavior for these systems at various mixing ratios was systematically investigated and was compared with that given by the Cates model. It was found that the Cates law can be applied in these systems simply by manipulating the mixing ratio or the surfactant structure. Energetic analysis demonstrates that the scaling behavior of wormlike micelles in nonequimolar mixed cationic and anionic surfactant systems can be close to that predicted by the Cates model, if the electrostatic contribution is below a threshold value.
Keywords: Wormlike micelles; Scaling behavior; Cates model; Catanionic surfactants; Mixed systems
Biocompatible lecithin-based microemulsions with rhamnolipid and sophorolipid biosurfactants: Formulation and potential applications
by Thu T.L. Nguyen; Ashley Edelen; Bridgett Neighbors; David A. Sabatini (pp. 498-504).
Successful microemusion formation using biosurfactant mixtures of lecithin, rhamnolipid and sophorolipid with isopropyl myristate (solid line) and limonene (dashed line) at 25°C.The objectives of this research are first to evaluate the hydrophilicity/hydrophobicity of sophorolipid biosurfactants relative to conventional synthetic surfactants and then to formulate and evaluate microemulsions of lecithin/rhamnolipid/sophorolipid biosurfactants with a range of oils (varying EACN values and oil types). We found that sophorolipid biosurfactants are more hydrophobic than sodium bis(2-ethyl) dihexyl sulfosuccinate (SBDHS), which is more hydrophobic than sodium dihexyl sulfosuccinate (SDHS) and rhamnolipid biosurfactant. Sophorolipid thus played an important role as the hydrophobic component in lecithin/rhamnolipid/sophorolipid biosurfactant formulation. This biosurfactant formulation was able to produce Winsor Type I, III and II microemulsions and the corresponding ultralow IFT for limonene, decane, isopropyl myristate and hexadecane. The phase behavior of this formulation with isopropyl myristate did not change significantly with changing temperature (10,25,40°C) and electrolyte concentration (0.9% and 4.0%w/v), making it desirable for cosmetic and drug delivery applications. The hexadecane detergency performance of our biocompatible formulation was higher than that of a commercial liquid detergent at the same surfactant active concentrations. This paper thus shows the ability and robustness of mixed biosurfactant systems in formulating microemulsions for a range of oils and their potential applications.
Keywords: Biocompatible; Rhamnolipid; Sophorolipid; Microemulsion; Phase behavior; Detergency
Effect of added monovalent electrolytes on the myelin formation from charged lipids
by Meiyu Lin; Li Li; Feng Qiu; Yuliang Yang (pp. 505-510).
Effect of NaCl concentration in hydrating solutions on the myelin formation from negatively charged cardiolipin. The scale bars represent 20μm. (a) Myelin figures with onion-like structures at 0.010M NaCl solution; (b) myelin figures at 0.150M NaCl solution and (c) thinner myelin figures with some irregular structures at 0.370M NaCl solution.The effect of added monovalent electrolytes on the myelin formation of cardiolipin is investigated by optical microscopy observations. The results show that the myelin formation strongly depends on the concentration rather than the type of electrolytes. Myelin figures are observed only in a certain concentration range of electrolytes, and the diameter of the myelin figures decreases with increasing of the electrolyte concentration. Furthermore, the theoretical model of myelin formation for the neutral lipids developed by Huang–Zou–Witten [J.R. Huang, L.N. Zou, T.A. Witten, Eur. Phys. J. E. 18 (2005) 279–285] is extended to the charged membrane system by taking into account the electrostatic interaction to understand the mechanism of myelin formation. The theoretical results well produce our experimental results.
Keywords: Myelin; Electrolyte; Electrostatic interaction; Charged lipid
X-ray grazing incidence diffraction and Langmuir monolayer studies of the interaction of β-cyclodextrin with model lipid membranes
by Michał Flasiński; Marcin Broniatowski; Jarosław Majewski; Patrycja Dynarowicz-Łątka (pp. 511-521).
Scheme of the cyclodextrin induced withdrawal of cholesterol from the investigated mixed monolayers.The interactions of β-CD with one component monolayers of cholesterol (chol), 1-stearoyl-sn-glycero-3-phosphocholine (lyso-PC), 1,2-dipalmitpyl-sn-phosphocholine (DPPC), sphingomyelin (SM) and the SM/chol and DPPC/chol mixtures have been investigated by the Langmuir monolayer technique and the synchrotron grazing incidence X-ray diffraction (GIXD). The investigated lipid monolayers have been studied with and without the 10−3M solution of β-CD in the aqueous subphase. The surface pressure–area ( π– A) isotherms and the relaxation of the monolayers (surface pressure–time curves) were monitored. Our experiments reveal that there is not impact of β-CD on the packing properties of the DPPC monolayers, while the presence of β-CD in subphase changes the in-plane organization of SM molecules. Monolayers composed of pure chol molecules have been rapidly affected by the presence of the β-CD in the subphase. Our data show that β-CD can complex and desorb one-chain phospholipid (lyso-PC) but this process is relatively slow and, as indicated by the GIXD data, β-CD molecules are present at the air/water interface.Subtraction of cholesterol by the β-CD from mixed binary systems containing SM/chol (70/30, 50/50 and 30/70mol ratio) and DPPC/chol (70/30 and 50/50mol ratio) has also been investigated. Our experiments proved that cholesterol can be removed from the mixed monolayers only when it is unbound. The β-CD was not capable to distract the monolayers of the SM/chol, forming a stable complex of the 2:1 stoichiometry (as observed in the model lipid raft). Interestingly, at the surface pressure of 30mN/m also at the molar proportion of 50/50 no cholesterol removal was observed. This was interpreted by relatively strong SM/chol interactions and the tight packing of the mixed monolayer. For model membranes, in which cholesterol was in large excess (SM/chol, 30/70) the β-CD extraction of cholesterol was observed, and the membrane composition evolves towards the lipid proportion corresponding to the stable complex stoichiometry (SM/chol 2:1).
Keywords: Lipid monolayers; β-cyclodextrin; Grazing incidence X-ray diffraction; Model lipid rafts
Cloud point phenomena of polyoxyethylene-type surfactants in ionic liquid mixtures of emimBF4 and hmimBF4
by Tohru Inoue; Yasutaka Iwasaki (pp. 522-528).
The cloud point of C14E5 in mixed ionic liquid composed of emimBF4 and hmimBF4 increases with hmimBF4 content in the mixture because of preferential interaction of the surfactant molecule with hmimBF4.Cloud point phenomena were observed for polyoxyethylene (POE)-type nonionic surfactants in ionic liquid mixtures composed of 1-ethyl-3-methylimidazolium tetrafluoroborate (emimBF4) and 1-hexyl-3-methylimidazolium tetrafluoroborate (hmimBF4). The cloud point temperature vs. concentration curve (cloud point curve) shifts toward higher temperatures with an increase in POE chain length and with a decrease in hydrocarbon chain length of the surfactants, reflecting the fact that POE chains and hydrocarbon chains act as a solvophilic group and a solvophobic group, respectively. The analysis of1H NMR chemical shifts revealed that hmimBF4 interacts with the surfactant preferentially in the ionic liquid mixture. Two liquid phases, one being surfactant rich and the other ionic liquid rich, coexist in equilibrium above the cloud point curve. In accordance with the preferential interaction of hmimBF4 with the surfactant, hmimBF4 is more concentrated in the surfactant-rich phase, while emimBF4 is more concentrated in the ionic liquid-rich phase compared with the composition of the original ionic liquid mixture. The temperature dependence of1H NMR chemical shifts suggests that the desolvation of hmim cation from the POE chains proceeds with an increase in temperature. In other words, the solvophilicity of the surfactant POE chain is reduced with temperature, which would be responsible for the liquid–liquid phase separation occurring at elevated temperature. The present results suggest that the property of ionic liquid as a solvent to support the self-assembly of amphiphilic compounds can be tuned by mixing two ionic liquid species, since the present surfactants show no cloud point in hmimBF4 solution and are immiscible with emimBF4.
Keywords: Polyethylene glycol alkyl ether; Nonionic surfactant; Cloud point in ionic liquid; Ionic liquid mixture; Surfactant–ionic liquid interaction
A Monte Carlo integration method to determine accessible volume, accessible surface area and its fractal dimension
by L. Herrera; D.D. Do; D. Nicholson (pp. 529-536).
Characterization for surface area and pore volume of a defective pore with a Monte Carlo integration scheme.We present a self-consistent Monte Carlo integration scheme to determine the accessible volume and the accessible surface area of a porous solid with known atomistic configuration. The new feature of this method is the determination of the variation of volume not only with respect to the distance from the surface (geometrical factor) but also with respect to the energy of the closest solid atom type. The variation with respect to distance gives us information about the area of the solid–fluid boundary (which is defined as one on which a spherical particle has zero solid–fluid potential energy) while the variation of the interfacial area of a contour at any distance from the surface, yields the surface curvature, for both convex and concave surfaces. On the other hand, the variation with respect to the type of solid atom yields information about the distribution of the area in terms of the heterogeneity of the surface. We illustrate our new method with a number of examples, ranging from a simple channel pore to complex solids, such as metal organic frameworks (MOF) and bundles of carbon nanotubes.
Keywords: Adsorption; Monte Carlo integration; Accessible volume; Accessible area; Fractal dimensions
Methylene blue adsorption by the waste of Abu-Tartour phosphate rock
by Gihan F. Malash; Mohammad I. El-Khaiary (pp. 537-545).
The multinearity in pore-diffusion plots indicate a decrease in the rate of diffusion of dye into smaller pores.Phosphate rock (PR) is an abundant ore and represents the basic raw material for the phosphatic fertilizer industry. Prior to industrial processing, PR is concentrated by grinding-and-screening to separate a fine fraction that is very poor in P2O5. This fine fraction is a solid waste and represents a disposal problem. The present study shows that the fine fraction of ground-and-screened Abu-Tartour PR can be used as an adsorbent for the removal of methylene blue dye from aqueous solutions. The amount of dye adsorbed was found to vary with initial methylene blue concentration and contact time. Raising the temperature enhances the rate of adsorption but has no effect on the adsorption capacity at equilibrium. The adsorption equilibrium data were found to fit the Langmuir isotherm, indicating monolayer adsorption on a homogeneous surface. The Elovich model can be used to predict the adsorption kinetics at ambient temperatures especially when the initial concentration of MB is relatively high, while Ho’s model deviates from the data as the initial concentration increases. However, as the temperature increases and MB concentration decreases, Ho’s model fits the data better than the Elovich model. On studying the mechanism of adsorption, the results showed that the overall rate of dye uptake is controlled by intraparticle diffusion. The multilinear plots of intraparticle diffusion were modeled by piecewise linear regression and related to pore-size distribution of the adsorbent.
Keywords: Adsorption; Isotherm; Kinetic; Methylene blue; Phosphate rock
Adsorption of polar and nonpolar compounds onto complex nanooxides with silica, alumina, and titania
by V.M. Gun’ko; G.R. Yurchenko; V.V. Turov; E.V. Goncharuk; V.I. Zarko; A.G. Zabuga; A.K. Matkovsky; O.I. Oranska; R. Leboda; J. Skubiszewska-Zięba; W. Janusz; G.J. Phillips; S.V. Mikhalovsky (pp. 546-558).
The adsorption capacity of mixed fume oxides for polar adsorbates is much greater than for nonpolar ones.Adsorption of low-molecular adsorbates (nonpolar hexane, nitrogen, weakly polar acetonitrile, and polar diethylamine, triethylamine, and water) onto individual (silica, alumina, titania), binary (silica/alumina (SA), silica/titania (ST)), and ternary (alumina/silica/titania, AST) fumed oxides was studied to analyse the effects of morphology and surface composition of the materials. Certain aspects of the interfacial phenomena dependent on the structural characteristics of oxides were analysed using calorimetry,1H NMR, and Raman spectroscopies, XRD, and ab initio quantum-chemical calculations. The specific surface area SBET,X-to-SBET,N2 ratio (X is an organic adsorbate) changes from 0.68 for hexane adsorbed onto amorphous SA8 (degassed at 200°C) to 1.85 for acetonitrile adsorbed onto crystalline alumina (degassed at 900°C). These changes are relatively large because of variations in orientation, lateral interactions, and adsorption compressing of molecules adsorbed onto oxide surfaces. Larger SBET,X/SBET,N2 values are observed for mixed oxides with higher crystallinity of titania or/and alumina phases in larger primary nanoparticles with greater surface roughness and hydrophilicity. Polar adsorbates can change the structure of aggregates of oxide nanoparticles that can, in turn, affect the results of adsorption measurements.
Keywords: Oxide nanoparticles; Complex fumed oxides; Structural characteristics; Nonpolar adsorbates; Polar adsorbates; Interfacial phenomena
Catalytic rate enhancement observed for alkyne hydrocarboxylation using ruthenium carbonyl-capped nanostructures
by Yuan Yi Chong; Wei Bin Goh; Sze Tat Tan; Wai Yip Fan (pp. 559-564).
[Ru2(MPA)4(CO)4] n oligomers-capped Ag nanocubes and nanoparticles show significant catalytic rate enhancement for alkyne hydrocarboxylation as compared to free ruthenium oligomers.Surface functionalization of Ag nanocubes and nanoparticles with catalytically active ruthenium carbonyl oligomers has been carried out successfully. These functionalized nanostructures catalyze hydrocarboxylation onto terminal alkynes at significantly enhanced rates (33 times) compare to those observed for free ruthenium oligomers. The rate enhancement is facilitated by adsorption of substrates on the surface of the nanoparticles, thus bringing them into close proximity with the catalyst. The size and shape of the Ag nanostructures were retained, indicating that the metallic cores act mainly as a docking site.
Keywords: Hydrocarboxylation; Catalysis; Ruthenium carbonyl; Silver nanocubes
Adsorption, immobilization, and activity of β-glucosidase on different soil colloids
by Jinlong Yan; Genxing Pan; Lianqing Li; Guixiang Quan; Cheng Ding; Ailan Luo (pp. 565-570).
Immobilized β-glucosidase on soil colloidal particles was more stable and less sensitive to the aging process than the free β-glucosidase.For a better understanding of enzyme stabilization and the subsequent catalytic process in a soil environment, the adsorption, immobilization, and activity of β-glucosidase on various soil colloids from a paddy soil were studied. The calculated parameters maximum adsorption capacity ( q0) for fine soil colloids ranged from 169.6 to 203.7μgmg−1, which was higher than coarse soil colloids in the range of 81.0–94.6μgmg−1, but the lower adsorption affinity ( KL) was found on fine soil colloids. The percentages of β-glucosidase desorbed from external surfaces of the coarse soil colloids (27.6–28.5%) were higher than those from the fine soil colloids (17.5–20.2%). β-Glucosidase immobilized on the coarse inorganic and organic soil colloids retained 72.4% and 69.8% of activity, respectively, which indicated the facilitated effect of soil organic matter in the inhibition of enzyme activity. The residual activity for the fine soil clay is 79–81%. After 30days of storage at 40°C the free β-glucosidase retained 66.2% of its initial activity, whereas the soil colloidal particle-immobilized enzyme retained 77.1–82.4% of its activity. The half-lives of free β-glucosidase appeared to be 95.9 and 50.4days at 25 and 40°C. Immobilization of β-glucosidase on various soil colloids enhanced the thermal stability at all temperatures, and the thermal stability was greatly affected by the affinity between the β-glucosidase molecules and the surface of soil colloidal particles. Due to the protective effect of supports, soil colloidal particle-immobilized enzymes were less sensitive to pH and temperature changes than free enzymes. Data obtained in this study are helpful for further research on the enzymatic mechanisms in carbon cycling and soil carbon storage.
Keywords: β-Glucosidase; Soil colloids; Adsorption; Immobilization; Activity; Thermal stability
The determination of oxide surface charging parameters for a predictive metal adsorption model
by Marc Schreier; Theresa E. Feltes; Melanie T. Schaal; John R. Regalbuto (pp. 571-578).
An optimization procedure was developed to predict oxide surface charging parameters from simple experimental procedures, which were then applied to enhance the prediction of metal adsorption for improved catalyst preparation.The procurement of oxide surface charging parameters has been a widely researched topic in recent years . In this study, a one-site, two- pK surface charging mechanism is used in combination with a diffuse double-layer description of the electric double-layer to fit pH shift data over silica and alumina. From these fits of pH data, with no further adjustment of parameters, metal adsorption can be predicted over both supports to a reasonable degree of accuracy.A multi-dimensional optimization procedure employing a Nelder–Mead simplex algorithm is used to optimize the Δ pK ( pK2– pK1) parameter to obtain a best fit of the pH shift data with fixed PZC and hydroxyl density (N s). The resulting set of parameters is then used with no adjustment in a purely electrostatic adsorption model (the Revised Physical Adsorption or RPA model) in order to predict anionic chloroplatinic acid (CPA, [PtCl6]−2) adsorption on alumina and cationic platinum tetraammine (PTA, [Pt(NH3)4]+2) adsorption on alumina and silica. The optimization procedure developed in this study gives reasonable values of the Δ pK compared to other values reported in the literature, with fits to the pH shift data at various oxide loadings with relative errors below 2.8%.
Keywords: Physical adsorption; pK; Platinum; Alumina; Silica
Fluoride removal from water by granular ceramic adsorption
by Nan Chen; Zhenya Zhang; Chuanping Feng; Norio Sugiura; Miao Li; Rongzhi Chen (pp. 579-584).
SEM reveals the surface morphology of the ceramic granules before adsorption and after adsorption.A new medium, granular ceramic, has been developed for fluoride removal from water. Granular ceramic is a solid-phase medium that produces a stable Al–Fe surface complex for fluoride adsorption. BET, SEM, and EDS were used to characterize the physical attributes (particle size, pore size and distribution, surface roughness) of the granular ceramic. Fluoride adsorption characteristics were studied in a batch system with respect to changes in initial concentration of fluoride, pH of solution, and coexisting ions. Fluoride adsorption was found to be pH dependent and the maximum removal of fluoride was obtained at pH 5.0–8.0. equilibrium adsorption data were obtained at 293, 303, and 323K, and interpreted in terms of the Langmuir and Freundlich isotherm equations. The experimental data revealed that the Freundlich isotherm equation gives a more satisfactory fit for fluoride removal. The adsorption process was observed to follow a pseudo-second-order kinetic model and intraparticle diffusion was indicated to play a major role in fluoride uptake. Fluoride adsorption was reduced in the presence of phosphate and sulfate ions and increased slightly in the presence of chloride and nitrate ions.
Keywords: Granular ceramic; Fluoride removal; Adsorption isotherms; Adsorption kinetics
Adsorption of bisphenol A from water by surfactant-modified zeolite
by Yi Dong; Deyi Wu; Xuechu Chen; Yan Lin (pp. 585-590).
Modification of zeolite with surfactant greatly enhanced the retention of bisphenol A from water. This figure shows the possible interaction mechanisms of bisphenol A with surfactant-modified zeolite.Zeolite synthesized from coal fly ash (ZFA) was modified with hexadecyltrimethylammonium (HDTMA) and was examined for the adsorption of bisphenol A (BPA) from water. Two ZFAs were prepared in our laboratory and were characterized to obtain chemical and mineralogical composition, surface area, and total and external cation-exchange capacity among other parameters. HDTMA was confirmed to form bilayer micelles on external surfaces of zeolites. Results indicate that, while ZFA had no affinity for BPA, the surfactant-modified ZFA (SMZFA) showed greatly enhanced adsorption capacity. Uptake of BPA was greatly influenced by pH, increasing at alkaline pH conditions which enable the deprotonation of BPA to form organic anions. The SMZFA with higher BET area and higher amount of loaded HDTMA showed greater retention for BPA. Uptake of BPA by SMZFA was improved slightly in the presence of NaCl, and was enhanced at a low temperature. We propose that BPA anions interact strongly with the positively charged heads of HDTMA, with the two hydrophobic benzene rings of BPA pointing to the inside of HDTMA bilayers. The adsorption of uncharged BPA probably involved hydrophobic partitioning into HDTMA bilayers and the coordination of the oxygen atoms of BPA with positively charged heads of HDTMA.
Keywords: Adsorption; Bisphenol A; pH; Mechanism; Surfactant; Zeolite
Surface complexation modeling of arsenic(III) and arsenic(V) adsorption onto nanoporous titania adsorbents (NTAs)
by Dong Suk Han; Ahmed Abdel-Wahab; Bill Batchelor (pp. 591-599).
The predicted model speciation of As(III) adsorbed on Ti(25)–SBA-15 at the lowest and highest initial As(III) concentrations. This figure shows the different contributions of surface species (mono- and bidentate binuclear surface complexes) over the range of pH examined.Nanoporous titania adsorbents (NTAs) were synthesised and applied to remove As(III) and As(V). Optimal pH ranges for As(III) removal were between pH 4 and pH 7 for Ti(25)–SBA-15 and between pH 8 and pH 11 for MT. Maximum removal efficiencies for As(V) by Ti(25)–SBA-15 were observed to be near pH 4 and the maximum for MT was in the pH range between pH 4 and pH 7. The SCM for As(III,V) adsorption by NTAs demonstrated the role of mono- and bidentate surface complexes in arsenic adsorption. For As(III) sorption on Ti(25)–SBA-15, monodentate surface complexes were more important than bidentate ones over the entire pH range investigated, but bidentate complexes played a role near pH 8. When As(III) was being sorbed onto MT, the model predicted that monodentate complexes dominate arsenic removal, except below pH 6 when a higher initial concentration was used. For As(V) adsorption, monodentate surface complexes are apparently responsible for As(V) removal over the entire pH range at both initial As(V) concentrations. At higher solid concentrations of Ti(25)–SBA-15, the patterns of surface speciation that were observed for both As(III) and As(V) adsorption were the same as those observed at lower solid concentrations. This behavior was also true for As(III) adsorbed to MT. For As(V) adsorption onto MT, however, the contribution of bidentate surface complexes at low pH became more intense than observed for lower solid concentrations with the same initial As(V) concentration.
Keywords: Surface complexation model; Arsenic(III); Arsenic(V); Adsorption; Nanoporous; Titania; Adsorbent
Eco-friendly and morphologically-controlled synthesis of porous CeO2 microstructure and its application in water purification
by Rajendra Srivastava (pp. 600-607).
An economical, eco-friendly and one-step synthesis route is developed for 3D flowerlike ceria nanostructure and the materials were utilized for the removal of As and Cr from water.A novel and eco-friendly route for the synthesis of porous CeO2 microstructure is reported. The citric acid mediated economical route is developed for the synthesis of a three-dimensional (3D) flowerlike micro/nanocomposite structure. Materials were characterized by a complementary combination of X-ray diffraction (XRD), nitrogen sorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron microscopy (XPS). CeO2 samples obtained have remarkably high surface area when compared to the commercial CeO2 sample. The surface area of CeO2 sample decreased upon calcination at higher temperature. However, the surface area is still almost 20 times more when compared to the commercial CeO2 sample. TEM investigation reveals that upon calcination at higher temperature, the size of the crystal increased but the short range order was merely disturbed. The analyses shows that the present method is suitable as a direct route for synthesizing nanoporous CeO2. Micro/nanocomposite CeO2 was found to be an excellent sorbent for the removal of poisonous pollutants present in water, such as arsenic (As) and chromium (Cr).
Keywords: Cerium oxide; Morphology-controlled synthesis; Nanoporous materials; Mesoporous CeO; 2; Water purification
Dynamics of supported lipid bilayer deposition from vesicle suspensions
by Seyda Bucak; Chen Wang; Paul E. Laibinis; T. Alan Hatton (pp. 608-614).
Schematic representation of the proposed mechanism of vesicle adsorption on silica.The equilibrium and dynamic adsorption behavior of mixed lipid (DMPC and DMPG) vesicles on a hydrophilic silica bead substrate indicate that the adsorption is a two-step process. Vesicles initially adsorb and spread on the silica surface as lamellar bilayer discs, with a rate mediated by the charge–charge interactions between vesicles and the silica beads. Vesicle adsorption occurs more readily on the growing discs than on the bare silica surface, and consequently the adsorption rate increases as the discs grow. Eventually, the growth is arrested because of unfavorable charge interactions between the discs as they cover more of the surface, and the equilibrium condition of partial surface coverage is attained.
Keywords: Solid-supported membranes; Liposomes; Surface coverage; Adsorption kinetics
Ammonia adsorption and its effects on framework stability of MOF-5 and MOF-177
by Dipendu Saha; Shuguang Deng (pp. 615-620).
FT-IR spectra of pristine and ammonia exposed MOF-5 and MOF-177.Ammonia adsorption equilibrium and kinetics on MOF-5 and MOF-177 were measured volumetrically at 298K and ammonia pressures up to 800torr. This study allowed us to determine the ammonia adsorption properties and stability of both MOFs after exposure to ammonia. MOF-177 adsorbed more ammonia than MOF-5 at ammonia pressures below 150torr and the ammonia adsorption capacity on both MOFs at 800torr was about the same (12.2mmol/g). It can be inferred from the adsorption results that physical adsorption of ammonia on both MOFs dominated at ammonia pressures below 150torr after which chemical reactions between ammonia and MOF frameworks take place. After exposure to ammonia both MOFs lost majority of their pore textures as evidenced by a drastic decrease of specific surface area and pore volume. The X-ray diffraction study suggested a complete loss of crystallinity of both MOFs, and the FT-IR and Raman spectral analyses showed the generation of free organic ligands within both MOF-5 and MOF-177 after they were exposed to ammonia. Ammonia molecules are proposed to destroy the MOF frameworks by forming hydrogen bonds with Zn4O clusters of MOFs.
Keywords: Ammonia; Adsorption; MOF-5; MOF-177; Framework stability
Adsorption of nitrosamines by mesoporous zeolite
by Wei Gang Lin; Feng Wei; Fang Na Gu; Xin Dong; Ling Gao; Ting Ting Zhuang; Ming Bo Yue; Jian Hua Zhu (pp. 621-627).
Mesoporous zeolite exhibits a good adsorption capacity in laboratory tests, superior to either microporous zeolite or mesoporous silica, providing a valuable candidate for controlling nitrosamines in the environment.On the basis of a study of the adsorption of zeolite and mesoporous silica, we attempted to create a hierarchical structure in the new nitrosamines trapper. Thus, mesoporous HZSM-5 zeolite was fabricated through impregnating a structure-directing agent into the as-synthesized MCM-41 followed by dry-gel conversion to transform amorphous silica to zeolite crystal. The texture of mesoporous ZSM-5 was tailored by adjusting the Si/Al ratio in the MCM-41 source and the thermal treatment time. The resulting samples were characterized by N2 adsorption to evaluate their textural properties. One volatile nitrosamine, N-nitrosopyrrolidine (NPYR), was used as probe molecule in instantaneous adsorption to survey the function of the resulting composites. Adsorptions of N′-nitrosonornicotine (NNN) in dichloromethane solution and tobacco-specific nitrosamines (TSNA) in tobacco-extract solution were also utilized for the same purpose. As expected, mesoporous zeolite exhibits a good adsorption capacity in laboratory tests, superior to either microporous zeolite or mesoporous silica, providing a valuable candidate for controlling nitrosamines in the environment.
Keywords: Mesoporous zeolite; Transformation; Nitrosamines; Adsorption
Adsorption–desorption studies of indigocarmine from industrial effluents by using deoiled mustard and its comparison with charcoal
by Vinod K. Gupta; Rajeev Jain; S. Malathi; Arunima Nayak (pp. 628-633).
Removal of indigocarmine over charcoal and deoiled mustard at different pHs.Deoiled mustard obtained from local oil mills has been used as an inexpensive and effective adsorbent for the removal of indigocarmine dye from industrial effluents. The influence of various factors on the adsorption capacity has been studied by batch experiments. The adsorption studies validate both Langmuir and Freundlich adsorption isotherms. Thermodynamic parameters such as Δ G°, Δ H°, and Δ S° for the adsorption process were calculated, which indicated the feasibility of the adsorption process. Desorption profiles revealed that a significant portion (85%) could be desorbed from deoiled mustard by using 30% glycerol as eluting agent.
Keywords: Adsorption; Deoiled mustard; Indigocarmine; Desorption
Wetting properties of silicon films from alkyl-passivated particles produced by mechanochemical synthesis
by Steffen Hallmann; Mark J. Fink; Brian S. Mitchell (pp. 634-641).
High energy ball milling presents a facile and efficient method to produce alkyl-passivated monocrystalline silicon particles for superhydrophobic coatings of arbitrary surfaces.A facile and efficient method using high energy ball milling (HEBM) to produce surfaces with a static and advancing contact angle in the superhydrophobic regime consisting of alkyl-passivated crystalline silicon particles is described. Deposition of the functionalized silicon material forms stable films on a variety of surfaces due to strong hydrophobic interactions between the individual particles. The process offers the ability to control the particle size from a micro-scale to a nano-scale region and thus to tune the surface roughness. Because of changing surface morphology and the decreasing surface roughness of the films due to the increasing milling times the static and dynamic contact angles follow a polynomial function with a maximum dynamic advancing contact angle of 171°. This trend is correlated to the commonly used Wenzel and Cassie-Baxter models.
Keywords: Silicon films; Monocrystalline silicon; High energy ball milling; Mechanochemical synthesis; Superhydrophobic properties
Electron transfer dynamics from the singlet and triplet excited states of meso-tetrakis( p-carboxyphenyl)porphyrin into colloidal TiO2 and AuTiO2 nanoparticles
by A. Kathiravan; R. Renganathan; S. Anandan (pp. 642-648).
Electron transfer dynamics of TCPP adsorbed on TiO2 and AuTiO2 nanoparticles have been investigated by time resolved absorption and fluorescence spectroscopy. The ket for TCPP–AuTiO2 is much faster than TCPP–TiO2.Electron transfer dynamics of meso-tetrakis( p-carboxyphenyl)porphyrin [TCPP] adsorbed on colloidal TiO2 and AuTiO2 nanoparticles have been investigated by time resolved absorption and fluorescence spectroscopy. Optical absorption studies reveal that the TCPP form complex with TiO2 and AuTiO2 nanoparticles. Excitation of TCPP adsorbed on the TiO2 nanoparticle surface leads to electron injection on the conduction band of TiO2. Electron injection has been confirmed by direct detection of cation radical of the adsorbed dye (TCPP+). The rate constant for the electron injection process is determined from both the singlet and triplet state respectively. The rate of electron injection for TCPP–AuTiO2 is much faster than TCPP–TiO2. The injected electrons are quickly transferred to Au and it escorts to ignore the back electron transfer (recombination) process.
Keywords: Colloidal AuTiO; 2; nanoparticles; Electron transfer dynamics; Back electron transfer
Novel electroless copper deposition on carbon fibers with environmentally friendly processes
by Jeong Hoon Byeon; Jang-Woo Kim (pp. 649-653).
An interesting deposition two-step process that is simple and effective is described, leading to copper film on fibers by initial activation (spark-generated silver nanoparticles) followed by liquid bath immersion.A novel electroless deposition (ELD) of copper (Cu) on carbon fibers (CFs) with environmentally friendly processes, silver (Ag) aerosol activation and subsequent nonformaldehyde Cu ELD, was developed. Spark-generated Ag aerosol nanoparticles (∼10nm in mode diameter) were deposited (48.4μgAg/gCF in activation intensity) onto the surfaces of CFs. After annealing (at 220°C in a nitrogen atmosphere), the catalytically activated CFs were placed into a solution for Cu ELD (at 82°C). Homogeneous Cu coating (∼5.1nm/min) on CFs was achieved with 90min of deposition and the corresponding mass deposition rate and Cu grain size for 30–90min of deposition had ranges of 0.25–1.14mgCu/gCF-min and 14.8–37.2nm, respectively. The porosity of CFs decreased by depositing the Cu for 30–90min, and the specific surface area and pore volume of CFs decreased from 1536 to 1399m2/g and from 0.65 to 0.57cm3/g, respectively.
Keywords: Electroless copper deposition; Carbon fiber (CF); Environmentally friendly process; Silver (Ag) aerosol activation; Nonformaldehyde ELD
Influence of short chain organic acids and bases on the wetting properties and surface energy of submicrometer ceramic powders
by Bram Neirinck; Dimitri Soccol; Jan Fransaer; Omer Van der Biest; Jef Vleugels (pp. 654-660).
The influence of short chained organics on the wetting properties and surface energy of ceramic particles was quantified by means of a modified Washburn method and DRIFT spectroscopy.The effect of short chained organic acids and bases on the surface energy and wetting properties of submicrometer alumina powder was assessed. The surface chemistry of treated powders was determined by means of Diffuse Reflectance Infrared Fourier Transform spectroscopy and compared to untreated powder. The wetting of powders was measured using a modified Washburn method, based on the use of precompacted powder samples. The geometric factor needed to calculate the contact angle was derived from measurements of the porous properties of the powder compacts. Contact angle measurements with several probe liquids before and after modification allowed a theoretical estimation of the surface energy based on the surface tension component theory. Trends in the surface energy components were linked to observations in infrared spectra. The results showed that the hydrophobic character of the precompacted powder depends on both the chain length and polar group of the modifying agent.
Keywords: Contact angle; Wettability; Submicrometer powders; Surface energy; Washburn
Effect of temperature and composition on the surface tension and thermodynamic properties of binary mixtures of 1-butyl-3-methylimidazolium thiocyanate with alcohols
by Urszula Domańska; Marta Królikowska (pp. 661-667).
The use of ionic liquids in separation processes might offer considerable potential for future technologies. Surface tension was measured in the binary solutions with alcohols and the thermodynamic functions were calculated.The surface tensions of pure ionic liquid, 1-butyl-3-methylimidazolium thiocyanate ([BMIM][SCN]), and binary mixtures of [BMIM][SCN] with alcohols (1-butanol, 1-pentanol, 1-hexanol) have been measured at atmospheric pressure at five temperatures in the range from 298.15 to 328.15K. These measurements have been provided to complete information of the influence of temperature on surface tension for the selected ionic liquid, which was chosen as a possible new entrainer in extraction processes. The surface thermodynamic functions such as surface entropy and enthalpy have been derived from the temperature dependence of the surface tension values, as well as the critical temperature, parachor, and speed of sound for pure ionic liquid. The investigations include the effect of the alkyl chain length of an alcohol and polarity of a solvent on the surface tension.
Keywords: Ionic liquid [BMIM][SCN]; +; alcohol (1-butanol, 1-pentanol, or 1-hexanol); Molecular interactions; Thermodynamic functions; Parachor; Experimental density and surface tension measurements; Speed of sound
Stimuli-responsive poly(4-vinyl pyridine) hydrogel nanoparticles: Synthesis by nanoprecipitation and swelling behavior
by Ana Arizaga; Gemma Ibarz; Rafael Piñol (pp. 668-672).
We describe the synthesis of stimuli-responsive poly(4-vinyl pyridine) nanospheres without crosslinker with high stability and swelling capacity. Their size varies significantly as a function of pH and ionic strength.Stimuli-responsive polymer nanospheres of poly(4-vinyl pyridine) have been obtained using a very simple modified nanoprecipitation technique. This process is conducted without help of crosslinking or monomer polymerization, methods used until now for this purpose. The influence of the surfactant concentration used in the preparation on particle size, the stability and the swelling kinetics of these hydrogels are studied. Furthermore, the nanospheres are shown to be pH and ionic strength responsive, undergoing swelling with equilibration times in the range of days. Dynamic light scattering and scanning electron microscopy were used to determine the structure, size, dispersion and morphology of these materials. Due to their response to stimuli, these nanoparticles are of potential interest for a number of biomedical applications such as drug delivery or biosensors.
Keywords: Colloids; Hydrogels; Nanoparticles; Stimuli-sensitive polymers; Swelling
Poly(N-isopropylacrylamide) (PNIPAM) is never hydrophobic
by Robert Pelton (pp. 673-674).
Phase separated PNIPAM contains too much water to be considered hydrophobic.PNIPAM chains have hydrophobic and hydrophilic domains below and above the LCST. Temperature dependent interactions between PNIPAM and solutes arise because of changes in the local environment around the hydrophobic isopropyl domains. Below the LCST the isopropyl groups are surrounded by water, whereas above the LCST the hydrophobic groups are in contact with both water and polymer segments. Contrary to numerous claims in the literature, PNIPAM is not a hydrophobic material at temperatures above the LCST.
Keywords: Keyword; PNIPAM LCST hydrophobicity