Journal of Colloid And Interface Science (v.297, #2)


Inner- and outer-sphere complexation of ions at the goethite–solution interface by Rasoul Rahnemaie; Tjisse Hiemstra; Willem H. van Riemsdijk (379-388).
Formation of inner- and outer-sphere complexes of environmentally important divalent ions on the goethite surface was examined by applying the charge distribution CD model for inner- and outer-sphere complexation. The model assumes spatial charge distribution between the surface (0-plane) and the next electrostatic plane (1-plane) for innersphere complexation and between the 1-plane and the head end of the diffuse double layer (2-plane) for the outersphere complexation. The latter approach has been used because the distance of closest approach to a charged surface may differ for different ions. The surface structural approach implies the use of a Three-Plane model for the compact part (Stern layer) of solid–solution interface, which is divided into two layers. The thickness of each layer depends on the capacitance and the local dielectric constant. The new approach has been applied to describe the adsorption of magnesium, calcium, strontium, and sulfate ions. It is shown that the concept can successfully describe the development of surface charge in the presence of Ca+2, Mg+2, Sr+2, and SO−2 4 as a function of loading, pH, and salt level, and also the shift in the isoelectric point (IEP) of goethite. The CD modeling revealed that, for the conditions studied, magnesium is mainly adsorbed as a bidentate innersphere complex, calcium can be a combination of bidentate innersphere and a monodentate inner- or outer-sphere complexes, and strontium is probably adsorbed as an outersphere complex. Sulfate is present as a mixture of inner- and outer-sphere monodentate complexes. Outersphere complexation is less pH dependent than innersphere complexation. The CD model predicts that the outersphere complexation of divalent cations and anions is relatively favorable at respectively low and high pH. Increase of ion loading favors the formation of innersphere complexes.
Keywords: Diffuse double layer; Basic Stern; Three-Plane model; Adsorption; Electrolyte ions; Calcium; Magnesium; Strontium; Barium; Iron oxide; Hematite; HFO; Magnetite; CD model; MUSIC model; Quantum chemical calculation;

An efficient multiscale-linking algorithm, based on the self-consistent integration of Brownian dynamics simulation of particle trajectories with the solution of the continuum-level conservation equation for particle concentration subject to an adaptive Neumann boundary condition that accounts for the blocking effect of deposition, is developed. The algorithm has been already validated in the case of deposition of noninteracting hard spheres [R.V. Magan, R. Sureshkumar, Multiscale Model. Simul. 2 (2004) 475]. In this study, the above algorithm is extended to incorporate particle interactions modeled by the DLVO theory. The simulations are used to identify a time scale at which the deposition process transitions from a power-law to an asymptotic regime. Detailed characterization of the two regimes is provided for a wide range of ionic strength, particle surface charge density, bulk volume fraction, and substrate potential values. The radial distribution functions obtained for various ionic strengths can be collapsed into a master curve when the radial distance is normalized with respect to a characteristic length scale of inter-particle repulsion. Moreover, simulation results suggest a rescaled, uniformly valid soft random sequential adsorption (RSA) model. Simulation results for the kinetics and monolayers structure compare favorably with experimental data, without the use of adjustable parameters. Comparison with other dynamic simulation techniques shows that while their predictions are qualitatively similar, notable quantitative differences exist especially for small ionic strengths.
Keywords: Brownian dynamics simulation; Irreversible deposition; Monolayer; Colloidal; RSA; DLVO; Multiscale;

Cooperativity in the adsorption of magnetic colloidal particles by K. Komaee; B. Yellen; G. Friedman; N. Dan (407-411).
In this paper we investigate the adsorption of magnetic particles onto magnetically patterned substrates. We find that the adsorption process is cooperative, where the probability of adsorption decreases with increasing substrate occupancy (namely, density of adsorbed particles). The effect of cooperativity can be accounted for by a simple modification of the adsorption probability as manifested by the binomial distribution. The negative cooperativity found in the magnetic particle adsorption is not due to direct repulsion between particles, but to screening of the surface's magnetic field by previously adsorbed particles. Thus, the adsorption of magnetic colloids on magnetic substrates is a self-limiting process.
Keywords: Colloid; Adsorption; Magnetic; Heterogeneous surfaces;

The maximum bubble pressure technique has been used to study the adsorption kinetics of binary mixtures of an anionic Gemini surfactant C9pPHCNa with a cationic conventional surfactant C10TABr in aqueous solutions. The dynamic surface tension data were analyzed using the revised Ward and Tordai equations as well as the micelle dissociation kinetic model suggested by Joos et al. The apparent diffusion coefficient D a below the cmc, the adsorption barrier ε a and the micelle dissociation constant k mic were obtained. The D a s at short times and at long times were respectively 0.2 – 16 × 10 10 and 0.08 – 0.9 × 10 10   m 2 s −1 , the latter corresponded to the adsorption barrier ε a of 10–20 kJ mol−1. The minimum ε a appeared at the mole fraction of C9pPHCNa ( α 1 , on a surfactant-only basis) in the bulk solution being 0.33. The k mic s of the mixed micelles were about 16–2300 s−1. The most stable mixed micelles were formed at α 1 = 0.2 rather than at α 1 = 0.33 owing to great discrepancy of hydrophobicity between the two components. These results indicated that the composition of mixed solution was an important factor affecting the adsorption kinetics and the micelle stability.
Keywords: Adsorption dynamics; Gemini surfactant; Cationic–anionic surfactants mixtures; Adsorption barrier; Micellar dissociation;

Adsorption of hexavalent chromium onto manganese nodule leached residues was investigated as a possible alternative to the conventional methods of its removal from aqueous synthetic solutions. Adsorption behavior was studied as a function of time, pH, temperature, and concentration of adsorbate and adsorbent in acetic acid–sodium acetate buffer medium. Cr (VI) removal was pH dependent and was found to be of a maximum at pH 3. The applicability of the Langmuir isotherm to the present system was tested. Increased adsorption capacity with increased temperature indicates that the adsorption reaction was endothermic in nature. Based on these studies, thermodynamic parameters such as Gibbs free energy change ( Δ G 0 ), standard enthalpy change ( Δ H 0 ), and standard entropy change ( Δ S 0 ) were calculated.Manganese nodule leached residue is a waste, which can be used as an effective adsorbent for removal of hexavalent Cr (80%) from aqueous solution at pH 3.
Keywords: Manganese nodule leached residues; Hexavalent chromium; Adsorption; Thermodynamic parameters;

Selective adsorption of phosphate from seawater and wastewater by amorphous zirconium hydroxide by Ramesh Chitrakar; Satoko Tezuka; Akinari Sonoda; Kohji Sakane; Kenta Ooi; Takahiro Hirotsu (426-433).
Phosphate adsorption from single electrolyte (NaH2PO4), phosphate-enriched seawater, and model wastewater was studied using amorphous zirconium hydroxide, ZrO(OH)2⋅(Na2O)0.05⋅1.5H2O, as an adsorbent. Batch experiments were carried out to investigate the adsorption of phosphate. The effect of pH on phosphate adsorption from seawater showed that the uptake of phosphate increased with an increase in pH up to 6, and then decreased sharply with a further increase in pH of the solution. The equilibrium data of phosphate adsorption were followed with a Freundlich isotherm. The uptake of phosphate at the adsorbent/solution ratio 0.05 g/2 L was 10 and 17 mg-P/g for the phosphate-enriched seawater and the model wastewater, respectively. A much higher adsorptivity toward phosphate ions in seawater was observed on ZrO(OH)2⋅(Na2O)0.05⋅1.5H2O than on other representative adsorbents based on layered double hydroxides of Mg(II)–Al(III), Mg(II)–Fe(III), and Ni(II)–Fe(III). The effective desorption of phosphate ions on ZrO(OH)2⋅(Na2O)0.05⋅1.5H2O could be achieved using a 0.1 M NaOH solution. The usefulness of experimental data for practical applications in removing phosphate in seawater and wastewater is discussed.ZrO2 has two types of hydroxyl groups, which are responsible for phosphate adsorption: (i) terminal ―OH groups exist on the surface of the solid, and (ii) bridging ―OH groups lie in the interior part of the solid and are connected by two metal atoms.
Keywords: Zirconium hydroxide; Adsorption; Selectivity; Phosphate; Seawater;

The performance of a conventional (F400) and a surface modified activated carbon (F400AN) has been investigated for the sorption of benazolin and 2,4-dichlorophenoxy acetic acid (2,4-D) from water. It was observed that the modified carbon, F400AN, which was obtained by annealing the conventional sample had a higher BET surface area (960 m2 g−1 compared to 790 m2 g−1) and it had a higher proportion of micropores. This was attributed to the loss of oxygen containing functional groups during the thermal treatment. Zeta potential and pH titration measurements also showed that acidic functionality had been lost on the F400AN sample. The adsorption data were analysed and were fitted well using the Langmuir isotherm. The modified carbon marginally out-performed the conventional activated carbon for sorption of these two herbicides. Thermodynamic parameters ( Δ G 0 , Δ H 0 , and Δ S 0 ) were determined and their values indicated that the sorption process was spontaneous and endothermic for both herbicides. A pseudo-second-order kinetic model was employed for analysing the kinetic data. It was concluded that the herbicide sorption process was controlled by a film diffusion mechanism.The performance of a conventional (F400) and a surface modified activated carbon (F400AN) has been investigated for the sorption of benazolin and 2,4-dichlorophenoxy acetic acid (2,4-D) from water. It was observed that the modified carbon, F400AN, which was obtained by annealing the conventional sample had a higher BET surface area (960 m2 g−1 compared to 790 m2 g−1) and it had a higher proportion of micropores. This was attributed to the loss of oxygen containing functional groups during the thermal treatment. Zeta potential and pH titration measurements also showed that acidic functionality had been lost on the F400AN sample. The adsorption data were analysed and were fitted well using the Langmuir isotherm. The modified carbon marginally out-performed the conventional activated carbon for sorption of these two herbicides. Thermodynamic parameters ( Δ G 0 , Δ H 0 , and Δ S 0 ) were determined and their values indicated that the sorption process was spontaneous and endothermic for both herbicides. A pseudo-second-order kinetic model was employed for analysing the kinetic data. It was concluded that the herbicide sorption process was controlled by a film diffusion mechanism.
Keywords: Activated carbon; Chemical treatment; Thermal treatment; Surface oxygen complexes; Characterisation; Benazolin; 2,4-Dichlorophenoxy acetic acid (2,4-D); Adsorption isotherm; Kinetic studies; Pseudo-second-order kinetic model;

Ferrous iron sorption by hydrous metal oxides by Genevieve Villaseñor Nano; Timothy J. Strathmann (443-454).
Ferrous iron is critical to a number of biogeochemical processes that occur in heterogeneous aquatic environments, including the abiotic reductive transformation of subsurface contaminants. The sorption of Fe(II) to ubiquitous soil minerals, particularly iron-free mineral phases, is not well understood. Colloidal TiO2, γ-AlOOH, and γ-Al2O3 were used as model hydrous oxides to investigate Fe(II) sorption to iron-free mineral surfaces. Rapid Fe(II) sorption during the first few hours is followed by a much slower uptake process that continues for extended periods (at least 30 days). For equivalent solution conditions, the extent of Fe(II) sorption decreases in the order TiO2 >γ-Al2O3γ-AlOOH. Short-term equilibrium sorption data measured over a wide range of conditions (pH, ionic strength, Fe(II)-to-sorbent ratio) are well described by the diffuse double layer model. Fe(II) sorption to TiO2 is best described by a single-site model that considers formation of two surface complexes, SOFe+ and SOFeOH0. For γ-AlOOH and γ-Al2O3, sorption data are best described by a two-site model that considers formation of SOFe+ complexes at weak- and strong-binding surface sites. Accurate description of sorption data for higher Fe(II) concentrations at alkaline pH conditions requires the inclusion of a Fe(II) surface precipitation reaction in the model formulation. The presence of common groundwater constituents (calcium, sulfate, bicarbonate, or fulvic acid) had no significant effect on Fe(II) sorption. These results demonstrate that iron-free soil minerals can exert a significant influence on Fe(II) sorption and speciation in heterogeneous aquatic systems.Iron (II) sorption to hydrous metal oxide surfaces is well described using the generalized diffuse double layrer (DDL) surface complexation model.
Keywords: Ferrous iron; Sorption; Surface complexation; Metal oxide; Titanium dioxide; Aluminum oxide; Anoxic environments;

Self-organization of 3,5-dihydroxybenzylalcohol (DHBA) based dendrimers of generations 0–3 (G0–G3) on bare and functionalized single crystal silicon (Si/SiO2) surfaces has been examined. The underlying monolayer plays a significant role in the supramolecular assembly leading to ordered structures of DHBA (G0) and generation 1–3 (G1–G3) dendrimers at interfaces. Ordered hyperbranched structures are formed on surfaces containing self-assembled monolayers with complimentary features to the assembling molecules, whereas no such organized assemblies are observed on unfunctionalized surfaces.Self-organization of 3,5-dihydroxybenzylalcohol (DHBA) based dendrimers of generations 0–3 (G0–G3) leads to ordered hyperbranched structures on surfaces containing self-assembled monolayers with complimentary features to the assembling molecules.
Keywords: Dendrimers; Molecular self-assembly; Monolayer interfaces; Surface crystallization;

Adsolubilization of 2-naphthol into an adsorbed layer of poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) triblock copolymers (Pluronics) on hydrophilic silica has been investigated. Four kinds of Pluronics (P103, P105, P123, and F108) were used in order to understand the effect of the hydrophobicity of surfactant on the adsolubilization. The order of the adsorption in the saturation level was found to be P123 ≈ P103 > P105 ≫ F108, meaning that Pluronics with higher hydrophobicity can adsorb preferentially to the silica surface. Indeed, this order was parallel to the order of the adsolubilization amount of 2-naphthol. In the case of co-addition of the Pluronics and 2-naphthol, the adsolubilization amount increased gradually at lower surfactant concentration regions, reached a maximum, and then decreased with increasing concentration of the Pluronics. The maximum amount appeared at critical polymolecular micelle concentration of each Pluronics. On the other hand, the final decrement was not observed when 2-naphthol was added after replacement of the Pluronics supernatant by the Pluronics free solution. These results suggest that adsolubilization behavior is influenced by the existence of the polymolecular micellar aggregates in the solution phase.Adsolubilization of 2-naphthol into an adsorbed layer of Pluronics on hydrophilic silica has been investigated. Four kinds of Pluronics (Pluronic P103, P105, P123, and F108) were used.
Keywords: Adsolubilization; Pluronics; 2-Naphthol; HLB; Dispersion stability;

Wettability of calcite and mica modified by different long-chain fatty acids (C18 acids) by K.A. Rezaei Gomari; R. Denoyel; A.A. Hamouda (470-479).
The effect of long-chain fatty acid adsorption on the wetting states of calcite and mica powders is investigated. The selected long-chain fatty acids are saturated or unsaturated aliphatic acids (stearic acid and oleic acid, respectively) and naphthenic acids with saturated or unsaturated aromatic rings (18-cyclohexyloctadecanoic acid and 18-phenoloctadecanoic acid, respectively). The amount of irreversibly adsorbed acid is determined by thermogravimetric analysis. The affinity of water and n-decane for these samples before and after modification is deduced from their adsorption isotherm and microcalorimetry. Thermodynamic analysis of surface pressure and spreading tension are performed based on adsorption isotherms. The enthalpy versus coverage curve for water adsorption and its comparison to liquefaction enthalpy is shown to be a meaningful method for characterizing the wettability of a surface. The naphthenic acid with unsaturated aromatic ring deeply modifies the calcite to an oil-wet state. The mica powder was not as strongly modified as calcite by these acid molecules.Characterization of a surface in terms of hydrophilicity/hydrophobicity determined by water vapor adsorption isotherm
Keywords: Wettability; Calcite; Mica; Long-chain fatty acids; Adsorption isotherms; Microcalorimetry; Energy of adsorption;

Nitrogen adsorption on a surface of a non-porous reference material is widely used in the characterization. Traditionally, the enhancement of solid–fluid potential in a porous solid is accounted for by incorporating the surface curvature into the solid–fluid potential of the flat reference surface. However, this calculation procedure has not been justified experimentally. In this paper, we derive the solid–fluid potential of mesoporous MCM-41 solid by using solely the adsorption isotherm of that solid. This solid–fluid potential is then compared with that of the non-porous reference surface. In derivation of the solid–fluid potential for both reference surface and mesoporous MCM-41 silica (diameter ranging from 3 to 6.5 nm) we employ the nonlocal density functional theory developed for amorphous solids. It is found that, to our surprise, the solid–fluid potential of a porous solid is practically the same as that for the reference surface, indicating that there is no enhancement due to surface curvature. This requires further investigations to explain this unusual departure from our conventional wisdom of curvature-induced enhancement. Accepting the curvature-independent solid–fluid potential derived from the non-porous reference surface, we analyze the hysteresis features of a series of MCM-41 samples.
Keywords: Density functional theory; Nitrogen adsorption; MCM-41 materials; Non-porous silica; Solid–fluid potential;

A new biosorbent for removing toxic metal ions from water/industrial wastewater has been investigated using by-product lignin from paper production. Lignin was extracted from black liquor waste, characterized and utilized for the removal of copper and cadmium from aqueous solutions in single, binary and multi-component systems. Adsorption studies were conducted at different temperatures, lignin particle sizes, pHs and solid to liquid ratios. All the studies were conducted by a batch method to determine equilibrium and kinetic parameters. The Langmuir and Freundlich isotherm models were applied. The Langmuir model fits best the equilibrium isotherm data. The maximum lignin adsorption capacities at 25 °C were 87.05 mg/g (1.37 mmol/g) and 137.14 mg/g (1.22 mmol/g) for Cu(II) and Cd(II), respectively. Adsorption of Cu2+ (68.63 mg/g at 10 °C and 94.68 mg/g at 40 °C) and Cd2+ (59.58 mg/g at 10 °C and 175.36 mg/g at 40 °C) increased with an increase in temperature. Copper and cadmium adsorption followed pseudo-second order rate kinetics. From kinetic studies, various rate and thermodynamic parameters such as effective diffusion coefficients, activation energy, and activation entropy were evaluated. Adsorption occurs through a particle diffusion mechanism at temperatures 10 and 25 °C while at 40 °C it occurs through a film diffusion mechanism. The sorption capacity of black liquor lignin is higher than many other adsorbents/carbons/biosorbents utilized for the removal of Cu(II) and Cd(II) from water/wastewater in single and multi-component systems.Kraft lignin derived from Eucalyptus black Liquor can be used as a metal ion adsorbent for treating water/wastewater contaminated with Cu(II) and/or Cd(II) in both single and multicomponent systems. The use of Kraft lignins as a value added adsorbent (over its fuel value), while simultaneously reducing the quantity of this waste, should be now considered. The sorption capacity of this biosorbent is higher than adsorbents/carbons/biosorbents now utilized for the removal of Cu(II) and Cd(II) from water/wastewater
Keywords: Lignin; Black liquor; Multi-component adsorption; Copper; Cadmium; Metal ions removal;

Monodisperse soap-free P(MMA-EA-MAA) latex particles were synthesized by seeded emulsion polymerization of methyl methacrylate (MMA), ethyl acrylate (EA) and methacrylic acid (MAA), and the particles with void morphology were obtained after undergoing alkali post-treatment. Effects of treatment conditions on particle morphology were investigated. Results showed that the void particles can be obtained under the conditions of the temperature >60 °C, initial pH >10.0, treatment time >20 min and 2-butanone amount >2.0 ml. The particle volume and the void size increased to the maximum and then decreased with the increases of initial pH and the treatment time, and these two values increased monotonously with the treatment temperature or 2-butanone amount increased. When the treatment temperature was elevated to 90 °C, the treatment time was longer than 180 min, or the 2-butanone amount was more than 8.0 ml, the relatively small voids inside most of the particles combined together to form a large one. The void structure disappeared completely as the initial pH was higher than 12.0. The generation mechanism of the void morphology was discussed.TEM photograph of P(MMA-EA-MAA) latex particles after alkali treatment at 80 °C.
Keywords: Soap-free latex particles; Seeded emulsion polymerization; Void morphology; Post-treatment; Mechanism;

The interaction forces between poly(N-isopropylacrylamide) (PNIPAAm)-grafted surfaces and colloidal particles in an aqueous solution were investigated using an atomic force microscope. Measurements were conducted between smooth silicon wafers on which PNIPAAm was terminally grafted and silica particles hydrophobized with a silanating reagent in an aqueous electrolyte solution under controlled temperature. Below the lower critical solution temperature (LCST) of PNIPAAm, there were large repulsive forces between the surfaces, both on approach and separation of the surfaces. On the other hand, above LCST, attractive forces were observed both in approaching and in separating force curves. When surface hydrophobicity of the particles increased, the maximum attractive force tended to increase. The changes of hydration state of the grafted PNIPAAm chains depending on temperature are considered to greatly alter the interaction force properties. The role of the intermolecular interaction between the PNIPAAm chains and the hydrophobic particles in the interaction forces is discussed.
Keywords: Atomic force microscope; Interaction force; Thermo-responsive polymers; N-Isopropylacrylamide; Graft; Colloidal particle; Hydrophobic interaction;

Vapor-induced film formation from low- T g particles for different solvent compositions by Ertan Arda; Selim Kara; Ayfer Sarac; Önder Pekcan (520-524).
The photon transmission method was used to study latex film formation from poly(vinyl acetate) (PVAc) particles induced by two different solvents. Films with the same latex content were prepared from PVAc particles and exposed to vapor of ethanol–water and acetone–water mixtures in various compositions. Transmitted photon intensities, I tr , from these films increased with increasing vapor exposure time. The increase in I tr is attributed to the increase in crossing density at the polymer–polymer junction. The Prager–Tirrell model was employed to obtain the back-and-forth frequency, ν, of the reptating polymer chain during film formation induced by solvent vapor. It was observed that the produced ν values increase as the solvent content is increased for both solvents. Abilities of both solvents to form films were interpreted with the solubility parameters of the solvents and the PVAc.Prager–Tirrell model was employed to obtain reptation frequency, ν, of PVAc chain during film formation induced by solvent vapor. The produced ν values increase as the acetone and ethanol content is increased.
Keywords: Film formation; Solvent vapor; Chain reptation; Reptation frequency;

Dynamic light scattering (DLS) measurement provides an effective way to investigate the formation of nanotube of γ-cyclodextrin (γ-CD) induced by N , N ′ -diphenylbenzidine (DPB) in water. With the combination of steady-state fluorescence and fluorescence anisotropy experiments, it was found that for α- and β-CD, only 1:2 (guest:host) inclusion complexes were formed and for γ-CD, cyclodextrin nanotube was formed involving 16 γ-CD units at maximum. The pH effect studies with both DLS and fluorescence anisotropy measurements indicated that the hydrogen bonding between neighboring CDs was necessary to the formation of cyclodextrin nanotube. In the temperature experiment, we found that the nanotube of DPB-γ-CD could exist stably at relatively high temperatures and the transition point for structural collapse was estimated to be around 54 °C. The aggregation states of both γ-CD itself and DPB-γ-CD nanotube were observed with TEM.
Keywords: Dynamic light scattering; Cyclodextrin nanotube; Fluorescence anisotropy; Hydrogen bonding; TEM;

Self-assembly in evaporated polymer solutions: Influence of the solution concentration by Edward Bormashenko; Roman Pogreb; Albina Musin; Oleg Stanevsky; Yelena Bormashenko; Gene Whyman; Oleg Gendelman; Zahava Barkay (534-540).
Amorphous polymers were dissolved in chlorinated organic solvents and deposited on thin horizontal substrates. The solutions with various concentrations of polymers were deposited and evaporated under ambient conditions in a slow air current. Self-assembled oriented mesoscopically scaled patterns were observed. The patterns were studied with optical and atomic force microscopy. The concentration of the solution exerts a decisive influence on the mesoscopic cell characteristic dimension. Cell dimensions grow linearly with the polymer solution concentration for all kinds of tested polymers, chlorinated solvents and substrates. The dependence could be explained by a physical mechanism, based on the mass transport instability occurring under the intensive evaporation of the solvent. In situ FTIR study of the process was performed first. It was established with FTIR spectroscopy that film porosity is not due to water droplet condensation under evaporation.3D AFM image of a typical mesoscopic cell formed on horizontal quartz glass substrate; polymer—PMMA, solvent—chloroform, concentration of the solution—10 wt%.
Keywords: Polymer solution; Concentration; Evaporation; Patterning; AFM microscopy; FTIR spectroscopy; Mass transport instability; Mesoscopic; Self-assembly; Pores;

Dispersion of organically modified clays within n-alcohols by N.H. Tran; G.R. Dennis; A.S. Milev; G.S.K. Kannangara; P. Williams; M.A. Wilson; R.N. Lamb (541-545).
A method for formation of polymer–clay nanocomposites involves dispersion of the nanometer silicate layers of clays into a solvent, followed by dispersion into polymers. The dispersion of layered silicates within solvents affects the structure and properties of the nanocomposites. We report the dispersion of organically modified clays, used for formation of nanocomposites with organic polymers, within a range of alcohol solvents. Experiments involved stirring a mixture containing approximately 1 wt% of alkylammonium-modified clays in n-alcohols with general molecular structure R n OH, where n represents the number of carbons of alkyl chains, varying from 2 to 8. The clays precipitated from the dispersion when R n OH solvents with n < 5 were used, however, they formed gels for solvents with n ⩾ 5 . The increased dispersion was related to the decrease of polarity and hydrogen bonding force within solvents. X-ray diffraction for the dispersed clays indicated that the interlayer spaces (1.8 nm), formed by regular stacking of the silicate layers, expanded to a maximum of 3.0 nm after treatment with R n OH with n ⩾ 5 . The interlayer expansion was due to the intercalation of n-alcohol molecules within the interlayer spaces. It is suggested that the alkyl chains of n-alcohols remain parallel to the silicate surface in the intercalate. Preliminary experiments on the influence of these alcohol solvents on the intercalation of polyol (polyether) are also reported.The interlayer spaces of the clays were expanded after dispersion within R n OH with n ⩾ 5 (n: number of carbons of alkyl chains). The expansion was due to the intercalation of n-alcohol molecules within the interlayer spaces. The alkyl chains of n-alcohols would remain parallel to the silicate surface of the clays.
Keywords: Organically modified clay; Cloisite 30B; Dispersion; Intercalation; X-ray diffraction; X-ray photoemission spectroscopy;

Interaction of small amounts of bovine serum albumin with phospholipid monolayers investigated by surface pressure and atomic force microscopy by Nara C. de Souza; Wilker Caetano; Rosangela Itri; Carlos A. Rodrigues; Osvaldo N. Oliveira; José A. Giacometti; Marystela Ferreira (546-553).
The influence of small amounts of bovine serum albumin (BSA) (nM concentration) on the lateral organization of phospholipid monolayers at the air–water interface and transferred onto solid substrates as one-layer Langmuir–Blodgett (LB) films was investigated. The kinetics of adsorption of BSA onto the phospholipid monolayers was monitored with surface pressure isotherms in a Langmuir trough, for the zwitterionic dipalmitoylphosphatidyl ethanolamine ( N , N -dimethyl-PE) and the anionic dimyristoylphosphatidic acid (DMPA). A monolayer of N , N -dimethyl-PE or DMPA incorporating BSA was transferred onto a solid substrate using the Langmuir–Blodgett technique. Atomic force microscopy (AFM) images of one-layer LB films displayed protein–phospholipid domains, whose morphology was characterized using dynamic scaling theories to calculate roughness exponents. For DMPA–BSA films the surface is characteristic of self-affine fractals, which may be described with the Kardar–Parisi–Zhang (KPZ) equation. On the other hand, for N , N -dimethyl-PE–BSA films, the results indicate a relatively flat surface within the globule. The height profile and the number and size of globules varied with the type of phospholipid. The overall results, from kinetics of adsorption on Langmuir monolayers and surface morphology in LB films, could be interpreted in terms of the higher affinity of BSA to the anionic DMPA than to the zwitterionic N , N -dimethyl-PE. Furthermore, the effects from such small amounts of BSA in the monolayer point to a cooperative response of DMPA and N , N -dimethyl-PE monolayers to the protein.The scheme (a) suggests that the most of the squeezed-out BSA/ N , N -dimethyl-PE complexes remain beneath, but close to the monolayer during the compression, being adsorbed back to the surface as the lateral pressure decreases. The scheme (b) suggests the BSA molecules are squeezed out from the DMPA monolayer, without any significant effect on phospholipid migration to the bulk phase. Again, when the monolayer is decompressed, the protein adsorbs back to DMPA monolayer.
Keywords: BSA; Protein; Interaction; Phospholipids; DMPA; N , N -dimethyl-PE; Langmuir films; LB films; AFM; Morphological analysis;

Aggregation of the biotemplates in mineralization processes is a considerable obstacle in preparing well-dispersed bio-inorganic hybrid materials. In this study, aggregation and mineralization of Tobacco mosaic virus (TMV) biotemplates were investigated as a function of the copper precursor (CuCl2) concentration. The mean hydrodynamic radius of TMV in an aqueous CuCl2 solution was determined by dynamic light scattering for the monitoring of the TMV aggregation. At CuCl2 concentration of 0.5 mM or higher, the mean hydrodynamic radius of TMV increased dramatically indicating aggregation of the TMV particles. Numerical calculations on the long-range interaction energy between parallel model TMV particles agreed with the experimental observations for the TMV aggregation. Mineralization of copper precursors on the TMV biotemplates was achieved only at the CuCl2 concentrations that induced considerable aggregation of the biotemplate. From the numerical calculations and experimental results, it was concluded that a dense copper cluster deposition cannot be achieved without aggregation of TMV templates.
Keywords: Tobacco mosaic virus; Copper; Interaction energy; Aggregation;

The molten globule (MG) state can be an intermediate in the protein folding pathway; thus, its detailed description can help understanding protein folding. Alkyl trimethylammonium bromides including dodecyl trimethylammonium bromide, DTAB; tetradecyl trimethylammonium bromide, TTAB; and hexadecyl trimethylammonium bromide, HTAB; cationic surfactants that are commonly used to mimic hydrophobic binding environments such as cell membranes, are known to denature some native state proteins, including horse cytochrome c (cyt c). In this article, refolding of alkaline and acid-denatured cyt c are studied under the influence of n-alkyl trimethylammonium bromides to form MG-like states at both low concentration (pH 11) and above the critical micelle concentration (pH 2) using ultraviolet and visible absorption, fluorescence and circular dichroism (CD). The addition of n-alkyl trimethylammonium bromides to the unfolded state of cyt c in alkaline and acidic condition appears to support the stabilized form of the MG state. The m-values of the refolded state of cyt c by DTAB, TTAB and HTAB showed substantial variation. The enhancement of m-values as the stability criterion of the MG state corresponded with increasing chain length of the cited n-alkyl trimethylammonium bromides. Based on the results obtained, the merits of two models of the protein-surfactant structure are discussed for various n-alkyl trimethylammonium bromides concentration in inducing the MG state at two different pH conditions. Therefore, hydrophobic interactions play a dominant role in stabilizing the MG state.The “necklace and bead” structure of protein–surfacant complexes and its two possibilities. (A) The protein wraps around the micelle. (B) The micelles nucleate on the protein hydrophobic sites. Separate “necklace bead” structures could explain the cyt c-cationic surfacants complexes behavior under different conditions. For 5 μM cyt c, the results suggest that the protein chain wraps around the micelle at below CMC (pH 11), whereas the micelle nucleates on the protein hydrophobic sites at high [n-alkyl trimethylammonium bromides] concentrations (upon to CMC at pH 2).
Keywords: Cytochrome c; Cationic surfactants; Molten globule-like state; Protein folding; Hydrophobic interaction; Stabilization;

Controlled organization of ZnO building blocks into complex nanostructures by Huihu Wang; Changsheng Xie; Dawen Zeng; Zhihong Yang (570-577).
ZnO complex nanostructure with special mushroom-like morphology was prepared by hydrolysis of zinc acetate dehydrate (Zn(CH3COO)2⋅2H2O) in water–methanol mixed solvent at 60 °C. The formation mechanism was studied using XRD investigation and FE-SEM observation, which showed that the mushroom-like particles were transformed from cauliflower-like layered basic zinc acetate (LBZA), Zn5(OH)8(CH3COO)2⋅2H2O, and composed of ZnO subunits with average size less than 10 nm. The introduction of hexamethylenetetramine (HMTA, C6H12N4) to the solution before deposition led to drastic changes in the morphologies of both aggregation particles and ZnO subunits. The novel ZnO microspheres, which were made of regular hexagonal plate-like ZnO with dimensional size 35 × 10   nm , were formed. These hexagonal plate-like ZnO subunits stacked very compactly and aligned regularly. Kinetic study of this unique complex nanostructure using TEM and FE-SEM observation showed the presence of HMTA played an important role on the formation of hexagonal ZnO subunits through different mechanisms related to the different parts of microspheres.A novel curved nanostructure that ZnO submicron spheres organized by the building blocks—hexagonal nanoplates
Keywords: Complex nanostructure; Building blocks; Microspheres; Controlled organization;

Nanofibers of barium strontium titanate (BST) by sol–gel processing and electrospinning by Santi Maensiri; Wiwat Nuansing; Jutharatana Klinkaewnarong; Paveena Laokul; Jinda Khemprasit (578-583).
This paper describes the fabrication of barium strontium titanate (Ba0.6Sr0.4TiO3 or BST) nanofibers by electrospinning method using a solution that contained poly(vinylpyrrolidone) and a sol–gel solution of BST. The as-spun and calcined BST/PVP composite nanofibers were characterized by TG-DTA, X-ray diffraction, FT-IR, SEM and TEM, respectively. After calcination of the as-spun BST/PVP composite nanofibers at above 700 °C in air for 2 h, BST nanofibers of 188 ± 25   nm in diameter having well-developed cubic-perovskite structure were successfully obtained. The crystal structure and morphology of the nanofibers were influenced by the calcination temperature. Calcination at below 700 °C resulted in amorphous phase whereas BST with second phase such as barium titanate were formed at above 700 °C. Diameters of the nanofibers decreased from 208 ± 35 to 161 ± 18   nm with increasing calcination temperature between 600 and 800 °C.
Keywords: Barium strontium titanate; Ferroelectrics; Perovskite; Nanofibers; Sol–gel processing; Electrospinning; Transmission electron microscopy; X-ray diffraction;

Phase transfer of gold nanoparticles from aqueous to organic solution containing resorcinarene by Tarun Kumar Misra; Tse-Shien Chen; Chuen-Ying Liu (584-588).
Citrate-capped gold nanoparticles (NPs) in aqueous solution were transferred directly into the organic solution mesitylene containing C-undecylcalix[4]-resorcinarene (C11-resorcinarene). C11-resorcinarene, which has long hydrophobic tails and phenolic hydroxyl groups, acted as both a phase-transfer and a capping agent. The C11-resorcinarene-capped gold particles could be isolated and dispersed in different organic solvents. Optical absorption spectra corresponding to surface plasmon resonance provided a broad band centered at 534 nm for C11-resorcinarene-capped gold NPs in mesitylene. High-resolution transmission electron micrograph images revealed that the average particle diameter of C11-resorcinarene-capped gold NPs is ∼12 nm.Citrate-capped gold nanoparticles (NPs) in aqueous solution were transferred directly into the organic solution mesitylene containing C-undecylcalix[4]-resorcinarene (C11-resorcinarene). Studies of optical absorption spectra and high-resolution transmission electron micrograph (HRTEM) images have demonstrated that C11-resorcinarene-capped gold NPs are well dispersed and stabilized in the organic solutions.
Keywords: Phase transfer; Organo-capped; Gold nanoparticles; Resorcinarene;

Uniform Y2O3 coating on multi-component phosphor powders by modified polyol process by Donjo Kim; Sunho Jeong; Jooho Moon; Seog Hyun Cho (589-594).
We have developed a method to coat the phosphors comprising of multi-component systems to prevent them from aging effect. Y2O3 was selected as a protective material because of its superior ability to resist against mercury adsorption and oxidation and its good UV transparency at the wavelength used for phosphor activation. By dispersing the phosphor particles in the polyol medium that contains the yttrium precursor, heterogeneous nucleation and growth on the particle surface were induced. This allows us to obtain a thick and uniform coating of the phosphors with amorphous Y2O3 sols. The heat-treatment condition for Y2O3 sols was carefully controlled to keep the phosphors from surface oxidation and at the same time to assure the complete crystallization and burn-out of organic impurity by XRD and TG/DTA. The surface morphology of the coated phosphors was examined by SEM as a function of reaction time and temperature and precursor concentration.We have developed a method to coat the phosphors comprising of multi-component systems to prevent them from aging effect using the modified polyol precess.
Keywords: Phosphor; Coating; Polyol process; Heterogeneous nucleation;

Selective recovery of polyhydroxyalkanoate inclusion bodies from fermentation broth by dissolved-air flotation by Pim van Hee; Andrea C.M.R. Elumbaring; Rob G.J.M. van der Lans; Luuk A.M. Van der Wielen (595-606).
Selective dissolved-air flotation for the separation of medium-chain-length polyhydroxyalkanoate (PHA) inclusion bodies (IBs) from Pseudomonas putida cell debris is investigated. Measurements show that both P. putida cell debris and PHA IBs have an iso-electric point of approximately pH 3.5. Selective aggregation and as a result selective flotation of PHA IBs was observed near this pH. Qualitative prediction of the aggregation behaviour was possible on the basis of the Van der Waals, hydrophobic and electrostatic interactions. In some cases however, the stability of the suspension could not be explained with these forces alone. It was therefore suggested that additional interactions, such as steric/brush effects, play an important role in the aggregation process.
Keywords: Particle–particle separation; Pseudomonas putida; Dissolved-air flotation; Polyhydroxyalkanoate (PHA); Inclusion body; Cell debris; Recovery;

The surface of ZnS and PbS has been modified by interfacing PbS on ZnS and ZnS on PbS nanoparticles. This produced core–shell nanocomposites ZnS/PbS and PbS/ZnS with tunable electronic properties. In both structures PbS particles are present in cubic form with an average diameter of about 6 nm. The addition of Pb2+ ( ⩾ 3 × 10 −4   mol dm −3 ) to Q-ZnS ( 1.5 × 10 −4   mol dm −3 ) in the basic pH range produces size-quantized fluorescent PbS particles coated by metal hydroxides. In these particles the relaxation kinetics of charge carriers has been followed using a picosecond single-photon counting technique. At ⩽ 1.5 × 10 −4   mol dm −3 Pb2+ an interfacial relaxation of charge from ZnS to PbS phase could be observed in subnanosecond time domain. An increase in [Pb2+] from 2 × 10 −4 to 1 × 10 −3   mol dm −3 enhanced the average emission lifetime from 9.4 to 19.4 ns. Composite PbS/ZnS particles are produced at high [ZnS] only. These particles had emission lifetime in μs time range. The extent of charge separation and the dynamics of charge carriers could be manipulated by the surface modification of these nanostructures.The interfacing of Q-ZnS with PbS and Q-PbS with ZnS has been utilized to produce tailored PbS nanocomposites with tunable electronic properties. The addition of smaller amounts of Pb2+ to ZnS produces Q-PbS particles at its interface whereas at its higher concentrations Pb(OH)2/Zn(OH)2 coated luminescent PbS nanoparticles are produced. Lifetime measurements of these nanocomposites demonstrate a rapid relaxation followed by the slow relaxation of charge in ZnS and PbS phases, respectively. The separation of charge is enhanced in case of PbS/ZnS core–shell particles. This aspect may have promising applications in the areas of photophysics, photonics and photocatalysis.
Keywords: Q-PbS; Photophysical properties; Q-ZnS/PbS; Q-PbS/ZnS; Nanocomposites;

Electrorheological analysis of nano laden suspensions by Karen Lozano; Carlos Hernandez; Troy W. Petty; Michael B. Sigman; Brian Korgel (618-624).
The synthesis and characterization of Pb3O2Cl2 nanowires and the electrorheological (ER) properties of carbon nanofiber (CNF), carbon nanotube (CNT) and Pb3O2Cl2 nanowire (NW) laden suspensions is presented. The ER properties were investigated through oscillatory shear experiments. The viscoelastic response in the presence of dc electric fields was analyzed. Actuation behavior for the CNF and NW laden suspensions was observed at low voltages and low concentration of the reinforcements (0.05 wt%). In the case of the CNT laden suspensions, an effect was observed at a concentration of 0.0125 wt%. Positive and negative electrorheological behaviors were observed due to differences in electrical conductivity and polarization mechanisms.(A) HRTEM image and (B) corresponding electron diffraction pattern of a NW oriented with respect to the [001] zone axis showing belt growth in the [010] direction.
Keywords: Nanotubes; Nanofibers; Nanowires; Actuators; Switches; Electrorheology; Microelectromechanical systems; Nanoelectromechanical systems;

Nano/micro-structure of bis(propyl)triethoxysilane substituted perylenediimide (1) with nanoparticle and twisted microrod morphologies were obtained by reprecipitation method induced by water and petroleum ether, respectively. It is believed that the different nucleation and growth processes involved are responsible for the formation of the nano/micro-structure with different morphologies of 1. UV–vis absorption and photoluminescence measurements show that their UV–vis absorption and photoluminescence properties are different from each other as well as their monomer and bulk materials due to the different effects on the charge transfer (CT) transition energy levels caused by their different aggregation behaviors.
Keywords: Morphologies; Nucleation; Optical properties; Organic nanostructures; Perylenediimide;

Breakup of carbon nanotube flocs in microfluidic traps by Paul R. Start; Steven D. Hudson; Erik K. Hobbie; Kalman B. Migler (631-636).
The critical stress to break flocs of multiwalled-carbon nanotubes suspended in low-molecular-weight polymer fluid is measured in planar elongational flow. Through image analysis of aggregates and their fragments, the extension rate of the flow and the size and aspect ratio of the aggregates are measured in real time. While trapping an aggregate at the stagnation point of the device, the flow rate is increased continually and breaking events are recorded, establishing a correlation between aggregate size and the critical elongation stress for fragmentation σ. This relationship resembles that for the breakup of flocs comprising spherical particles, yet it indicates that the strength of these fibrous flocs depends much more strongly on the local particle concentration. Fracture avalanches (or cascades) are also observed.The critical stress to break flocs of multiwalled-carbon nanotubes suspended in low-molecular-weight polymer fluid is measured in planar elongation flow produced in a microfluidic trap.
Keywords: Dispersion; Breakup; Nanotubes; Flocs; Microfluidics; Elongational flow;

Self-assembly of Ag nanoparticle–biotin composites into long fiberlike microstructures by Shweta Hegde; Sudhir Kapoor; Satyawati Joshi; Tulsi Mukherjee (637-643).
An end-to-end assembly of spherical Ag nanoparticles takes place in the presence of biotin to form long fiberlike microstructures. These microstructures are about 4 μm long with a thickness of 1 μm, obtained from SEM studies. TEM studies showed the presence of spherical silver nanoparticles having an average size of 20 nm. ATR–FTIR studies revealed that silver ions interact with biotin involving the carboxylate group. A weak binding of the silver particles with the thioether and ureido groups helps in connecting the Ag nanoparticles to form long fiberlike structures. Elucidation of the mechanism of formation of the spherical Ag clusters was done by pulse radiolysis.
Keywords: Ag nanoparticles; Fiberlike microstructures; Biotin;

A rapidly convergent series for calculation of the interaction energies between two similar plane double-layers for z + / z − = − 2 asymmetric electrolytes at positive surface potential are obtained by introducing a parameter λ in elliptical integral. When dimensionless surface potential is less or equal to 20, the number of the series terms required to obtain the interaction energies with six significant digits are not more than 4. The accurate numeral results are given and they can be used to check up the validity of approximate expressions people obtain. The present results are also fit for z + / z − = − 1 / 2 asymmetric electrolytes at negative surface potential. V z − z ′ and V ′ in the figure are the interaction energies of symmetric and z + / z − = − 2 asymmetric electrolytes at y > 0 , respectively. V z − z ′ must intersect V ′ at a certain ξ d . When ξ d is smaller V ′ > V z − z ′ ; when ξ d is larger, V ′ < V z − z ′ . The difference value ( V ′ − V z − z ′ ) increases with the increase of y 0 .
Keywords: Rapidly convergent series; Double layers; Interaction energies; Asymmetric electrolytes; Elliptical integral;

Lamellar nanocomposites based on exfoliated SbP 2 O 8 − nanosheets and ionic polyacetylenes by G.K. Prasad; N. Kumada; J. Yamanaka; Y. Yonesaki; T. Takei; N. Kinomura (654-659).
Novel lamellar nanocomposites composed of exfoliated SbP 2 O 8 − nanosheets and poly(N-methyl-2-ethynyl pyridinium iodide) (PNMe) or poly(N-octadecyl-2-ethynyl pyridinium bromide) (PNO) have been synthesized by exfoliation and re-stacking method. The XRD data of the nanocomposites SbP 2 O 8 − :PNMe and PNO: SbP 2 O 8 − indicate the formation of nanostructures containing SbP 2 O 8 − nanosheets and PNMe or PNO with interlayer expansions of 2.22 and 4.2 nm along the stacking direction of SbP 2 O 8 − nanosheets. Formation of these nanocomposites is further supported by the results obtained by FT-IR spectroscopy, scanning transmission electron microscopy and thermogravimetry. The values of electrical conductivity of the polymers and nanocomposites have also been measured.Novel lamellar nanocomposites composed of exfoliated SbP 2 O 8 − nanosheets and poly(N-methyl-2-ethynyl pyridinium iodide) (PNMe) or poly(N-octadecyl-2-ethynyl pyridinium bromide) (PNO) have been synthesized by exfoliation and re-stacking method. The XRD data of the nanocomposites SbP 2 O 8 − :PNMe and PNO: SbP 2 O 8 − indicate the formation of nanostructures containing SbP 2 O 8 − nanosheets and PNMe or PNO with interlayer expansions of 2.22 and 4.2 nm along the stacking direction of SbP 2 O 8 − nanosheets. Formation of these nanocomposites is further supported by the results obtained by FT-IR spectroscopy, scanning transmission electron microscopy and thermogravimetry. The values of electrical conductivity of the polymers and nanocomposites have also been measured.
Keywords: Lamellar nanocomposites; Nanosheets; Re-stacking; Nanostructure;

Synthesis of Ag–Fe3O4 heterodimeric nanoparticles by Ling Zhang; Yong-Hua Dou; Hong-Chen Gu (660-664).
We report a general synthetic method for construction of size-controlled Ag–Fe3O4 heterodimeric nanoparticles using the Fe3O4 nanoparticles as the seeds. The Ag–Fe3O4 heterodimeric nanoparticle can be controlled by tuning the size of the Fe3O4 seed and reaction conditions for synthesis of the Ag nanoparticles grown on it. The as-synthesized nanoparticles can be readily converted into aqueous-soluble form with newly introduced functional groups on the surface of Ag–Fe3O4 heterodimeric nanoparticles.The Ag–Fe3O4 (9–12 nm) heterodimeric nanoparticle can be constructed by synthesis of Ag nanoparticle grown on the Fe3O4 seed.
Keywords: Heterostructure; Magnetite; Nanoparticles; Nanostructure; Silver;

Inner-sphere adsorption geometry of Se(IV) at the hematite (100)–water interface by Jeffrey G. Catalano; Zhan Zhang; Paul Fenter; Michael J. Bedzyk (665-671).
The 3-dimensional structure of adsorption complexes on mineral surfaces provides insight into the fundamental mechanisms controlling sorption processes. This is important to the development of a general understanding of the behavior of contaminants such as selenite in the environment. The adsorption of selenite (SeO2− 3) on the hematite (100) surface was studied using X-ray standing wave (XSW) measurements. Inner-sphere bidentate surface complexes bridging between adjacent singly-coordinated oxygen sites were identified as the primary adsorption site. The lack of binding to doubly-coordinated oxygen sites that were also exposed on the surface was likely due to differences in the reactivity or exchange kinetics of these sites or cation–cation repulsion, although the latter appears to be a secondary effect based on past observations. While these bridging bidentate geometries are similar to those inferred in past spectroscopic studies, the Se–Fe distances are such that these species might be misidentified as edge-sharing complexes if studied by EXAFS spectroscopy, highlighting the need for a fundamental understanding of mineral surface structure.Selenite forms bidentate inner-sphere surface complexes bridging between adjacent singly-coordinated oxygen sites at the hematite (100)–water interface.
Keywords: Selenite; Hematite; Inner-sphere adsorption; XSW;

Calcination of a cerium-S-phenylene-O-holmium-O-phenylene-S hybrid copolymer under a vacuum gave cerium oxide–carbon cluster–holmium oxide composite material. The material calcined at 600 °C loaded with Pt particles could decompose water to H2 and O2 with a H2/O2 ratio of 2 under visible light irradiation. ESR spectral examinations of the calcined materials revealed the possibility of a two-step electron transfer in the process of CeO2 → carbon cluster → Ho2O3 → Pt with an oxidation site at CeO2 particles and a reduction site at Pt particles.
Keywords: Cerium oxide–carbon cluster–holmium oxide composite material; Two-step electron transfer; Water photodecomposition;

Adsorbability and photocatalytic degradability of humic substances in water on Ti-modified silica by Takeshi Moriguchi; Muneaki Tahara; Kazuhiko Yaguchi (678-686).
From the viewpoint of development of a removal agent for humic substances, we prepared Ti-modified silica gel, SiO2–Ti, from titanium alkoxide and microsized silica gel. The prepared silica agent was investigated in adsorption and photocatalytic degradation of humic substances in water. In these experiments, four humic substances, commercially available Wako humic acid (Wako-HA), Nordic aquatic humic acid (Nordic-HA), Nordic aquatic fulvic acid (Nordic-FA), and Suwannee river fulvic acid (Suwannee-FA), were used, and Freundlich constants ( K F and 1 / n ) and photodegradation rates were evaluated. Wako-HA, which has the highest aromaticity ratio [Ar–OH]/[COOH] and molecular weight, had the highest adsorbability ( K F = 17.5   ( mg / g ) ( L / mg ) 1 / n , 1 / n = 0.67 ) but the lowest photodegradability (<80%). On the other hand, Suwannee-FA, which has the lowest aromaticity, [Ar–OH]/[COOH] ratio, and molecular weight, afforded lesser adsorbability ( K F = 7.1   ( mg / g ) ( L / mg ) 1 / n , 1 / n = 0.39 ) but the highest photodegradability (>99%). Nordic-HA and Nordic-FA afforded adsorbabilities similar to that for Suwannee-FA, and medium photodegradabilities between those for Wako-HA and Suwannee-FA. Adsorption and photodegradation capacities of SiO2–Ti were improved with increased Ti content and phosphorescence emission amount, respectively. From XRD analysis, we found that the structure of anatase-type TiO2 features the Ti modifiers of SiO2–Ti. Therefore, humic substance molecules effectively interact with the Ti modifiers and are decomposed by OH radicals generated in situ. We hope that SiO2–Ti will be used as a photodegradation catalyst in water purification plants.This paper describes that Ti-modified silica prepared can be used as a removal agent for humic substances from water by adsorption and photodegradation mechanisms.
Keywords: Titanium; Silica gel; Humic substances; Freundlich constants; Adsorption; Photocatalytic degradation;

We have investigated the electrocatalytic dehalogenation of β-methylallyl chloride (β-mAC), widely used in the polymer industry, using [Co(I)(bpy)3]+ (where bpy = 2,2′-bipyridine) electrochemically generated in situ from [Co(II)(bpy)3]2+ at a glassy carbon electrode in the presence of three different cationic surfactants in aqueous solution. Cetyltrimethylammonium bromide (CTAB), tetradecyltrimethylammonium bromide (TDTAB), and cetylbenzyldimethylammonium chloride (CBDAC) were employed in the present investigation. The [Co(II)(bpy)3]2+–cationic surfactant systems show excellent electrocatalytic activity toward dehalogenation of β-mAC. The dependence of the catalytic current, the corresponding potential, and the current function on the potential scan rate has been analyzed to assess the nature of the catalytic reaction. The second-order rate constant, k chem, for the reaction between the β-mAC substrate and the electrogenerated-micelle stabilized-Co(I) complex has been calculated by a cyclic voltammetry technique. The reduction products after 3 h of bulk electrolysis have been identified by GC/MS to be one nonchloro compound (2-methyl-1,5-hexadiene (IV)) and two chloro compounds (1-chloro-2,5-dimethyl-2,5-hexadiene (V) and spiro[1.2]cylopropyl-6-chloro-5-methyl-hex-4-ene (VI)). Based on the electrochemical results and the mass spectral data, a reaction scheme involving all the reduction products has been proposed. Finally, a good correlation between the catalytic efficiency and the structural features of the surfactant molecules is demonstrated. The present study emphasizes the need for further optimization work to achieve maximum yield of nonchloro compound (IV) to employ the present [Co(II)(bpy)3]2+–cationic surfactant systems with a high catalytic efficiency as promising for possible applications.Electrochemically generated Co(I) bipyridine complex stabilized by micellar aggregates of cationic surfactant (CTAB or TDTAB or CBDAC) has been used for mediated reduction of β-methylallyl chloride in aqueous solutions, and a good correlation between structural features of surfactant molecules and the efficiency of the catalytic mediation reaction has been demonstrated.
Keywords: Electrochemical mediated catalysis; ECCAT mechanism; Second-order rate constant; Outer sphere electron transfer mechanism; Micellar stabilization; GC/MS;

The dissolution behavior of montroydite (HgO) has been studied using a fully automated system. Dissolution data under equilibrium conditions are in agreement with previously published data and indicate that HgO solubility is relatively high and constant between pH 4 and 10.1 and increases markedly at pH < 4. The dissolution rate also has similar behavior: it is relatively high and constant between pH 4 and 10.1 and increases sharply at pH < 4. The dissolution process obeys a three-dimensional contraction or attrition mechanism. The dissolution rate increases with increasing temperature and stirring rate and is the result of mixed transport and reaction control. The rate of HgO dissolution is considerably higher than that of other divalent metal oxides at low pH. This high rate is due to the ability of Hg(II) to rapidly exchange its ligands. Data suggest that montroydite will only occur in nature in highly contaminated sites and indicate that Hg oxidation products that are formed at the liquid Hg/water interface may dissolve rapidly.The high dissolution rate of HgO is a consequence of the ability of Hg(II) to rapidly exchange its ligands, and explains why HgO is rarely found in the environment.
Keywords: Mercury oxide; Dissolution kinetics; Dissolution mechanism; Oxide minerals;

Nano-sized poly(ethylene glycol dimethacrylate-co-acylic acid) (poly(EGDMA-co-AA)) were effectively self-assembled on poly(divinylbenzene-co-styryl methylpyridinium chloride) (poly(DVB-co-StMPyCl)) surfaces to form the raspberry-like composite by a charge compensation mechanism through the affinity complex between carboxylic group and pyridinium group. The effects of pH and salt electrolyte on the morphology of the self-assembled polymer composites were investigated. The resulting heterocoagulates were highly stable in water and acid solution. These heterocoagulates were reversible through the self-assembly in acidic or neutral media and the dissociation in the basic medium due to the charge compensation through the strong affinity complex between hydroxide anion and pyridinium group cation. The resulting heterocoagulates were characterized with scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM) and Fourier transform infrared spectroscopy (FTIR). As a result, a new method for tuning the structure of a charge compensation directed polymer composite was developed.
Keywords: Affinity complex; Charge compensation; Composite polymer; Self-assemble; Raspberry-like polymer;

Dynamic instability at liquid/vapor interface far from equilibrium by R.P. Rastogi; R.C. Srivastava; Y.K. Agrawal (711-714).
Attempt has been made to elucidate the mechanism of electric potential oscillations at oil–aqueous solution interface involving adsorption at oil–vapor interface on a semi-theoretical basis. The mechanism stipulates adsorption of ammonia, amines and pheromones at the liquid–vapor interface followed by transfer of ions through membrane–aqueous solution interface and subsequent interaction of ammonium (amine) ions and carbocations from pheromones with diffusing halide ions from the bulk. Relationship of the above mechanism with sensing mechanism of smell by olfactory nerves has also been pointed out.Schematic diagram of Yoshikawa oscillator: A = 0.5 M NaCl, B = 0.5 M KCl, C = millivoltmeter, D = liquid membrane (4.5 mm), E = cotton-soaked solution of olfactory agent in a tube, ammonia in the present case.
Keywords: Interfacial oscillations; Non-linear science; Electrophysiology; Dynamic instability at interface;

The oxide content in Al powders has been found to have a significant effect on the expansion and stability of foams made via a PM route. With low oxide contents (O < 0.3 wt%) expansion is moderate and the foam structure is unstable. Larger expansions, improved foam stability and more homogeneous foam structures are achieved if the amount of oxide in the powder is moderate (O = 0.3–0.6 wt%). Foaming precursors with excessive oxide contents (O > 0.6 wt%) results in small expansions but very stable foam structures. Oxides were observed to form clusters of crumpled films, which at higher levels form a network which restricts the drainage of liquid from the cell walls and Plateau borders, but which also inhibit foam expansion. Oxide clusters in the cell walls lead to a decrease in the minimum cell wall thickness, resulting in an increase in foam expansion.The oxide content in Al powders has been found to have a significant effect on the expansion and stability of foams made via a PM route. With low oxide contents (O < 0.3 wt%) expansion is moderate and the foam structure is unstable. Larger expansions, improved foam stability and more homogeneous foam structures are achieved if the amount of oxide in the powder is moderate (O = 0.3–0.6 wt%). Foaming precursors with excessive oxide contents (O > 0.6 wt%) results in small expansions but very stable foam structures. Oxides were observed to form clusters of crumpled films, which at higher levels form a network which restricts the drainage of liquid from the cell walls and Plateau borders, but which also inhibit foam expansion. Oxide clusters in the cell walls lead to a decrease in the minimum cell wall thickness, resulting in an increase in foam expansion.
Keywords: Aluminium; Metallic foam; Oxides; Powder processing;

Synthesis of high surface area Al-containing mesoporous silica from calcined and acid leached kaolinites as the precursors by Chengala D. Madhusoodana; Yoshikazu Kameshima; Akira Nakajima; Kiyoshi Okada; Toshihiro Kogure; Kenneth J.D. MacKenzie (724-731).
Al-containing mesoporous silicas were synthesized by hydrothermal treatment of microporous silica prepared by selectively acid leached metakaolinites with Si/Al = 3.9–92.5 mixed with a surfactant of cetyltrimethylammonium bromide (CTABr). The specific surface area of the products increased with higher surfactant/microporous silica (surf/Si) ratio and Si/Al ratio of the microporous silica, reaching about 1400 m2/g at CTABr/Si ⩾ 0.1 and Si/Al ⩾ 40. The XRD patterns of these products show a hexagonal (100) peak with the lattice parameter a 0 = 4.2 – 4.3 nm and the N2 adsorption isotherms show steep increase of adsorption between relative pressure of 0.3 and 0.4. Hexagonal mesoporous microstructure is observed by high resolution TEM. The pore size distributions of the products show a sharp peak at 2.8 nm by the BJH method. The high specific surface area of the present mesoporous samples is attributed to the lower matrix density and surface roughness of mesopore wall. The highest specific surface area of the products reached up to 1420 m2/g and this value is apparently higher than those reported in hexagonal mesoporous silicas. A unique microporous structure of the starting material is thought to be related to achieve such a high specific surface area of the products.
Keywords: Al-containing mesoporous silica; Specific surface area; Microporous silica; Cetyltrimethylammonium bromide; Kaolinite;

Measurement of thickness and composition of a solvent film on a bubble by H.M. Tarkan; S. Gélinas; J.A. Finch (732-737).
Solvent-coated air bubbles in the air-assisted solvent extraction (AASX) process achieve the dual role of high solvent specific surface area and ease of phase separation. The properties and thickness of the solvent film control the process. As an approach to the study, the layer interferometry (in the UV–vis region) and FT-IR spectroscopy were used to measure the time dependent thickness and chemical composition, respectively, of a film formed by blowing an air bubble in kerosene-based solvents. The film was stabilized by the presence of 1.5 ppm silicone oil, as employed in AASX. The film appears to comprise two layers; an outer layer of almost constant thickness and an inner layer which decreased in thickness with time. The latter is considered relevant to AASX. Generally, the initial thickness was ∼ 3   μm which decreased over several minutes to a final rupture thickness of ⩽ 500   nm . The initial thickness is of the order determined indirectly. The chemical composition of the layer did not change with time.The layer interferometry and FT-IR spectroscopy were used to measure the time dependent thickness and chemical composition, respectively, of a film formed by blowing an air bubble in kerosene-based solvents.
Keywords: Thin film; UV–visible; FT-IR; Coated bubble;

Pore-network study of the characteristic periods in the drying of porous materials by Andreas G. Yiotis; Ioannis N. Tsimpanogiannis; Athanassios K. Stubos; Yannis C. Yortsos (738-748).
We study the periods that develop in the drying of capillary porous media, particularly the constant rate (CRP) and the falling rate (FRP) periods. Drying is simulated with a 3-D pore-network model that accounts for the effect of capillarity and buoyancy at the liquid–gas interface and for diffusion through the porous material and through a boundary layer over the external surface of the material. We focus on the stabilizing or destabilizing effects of gravity on the shape of the drying curve and the relative extent of the various drying periods. The extents of CRP and FRP are directly associated with various transition points of the percolation theory, such as the breakthrough point and the main liquid cluster disconnection point. Our study demonstrates that when an external diffusive layer is present, the constant rate period is longer.
Keywords: Porous media; Drying; Pore-network model; Invasion percolation; Drying curve;

This work was a study of the chemical modification of diatomaceous earth (DE) using hydrofluoric acid (HF) solution. Under the experimental conditions investigated, it was found that HF under controlled conditions significantly etched inward into the interior of the existing pore structure in the clay mineral due to its high content of silica, leaving a framework possessing a larger BET surface area (ca. 10 m2 g−1) in comparison with that (ca. 4 m2 g−1) of its precursor (i.e., DE). Further, the results indicated that the HF concentration is a more determining factor in creating more open pores than other process parameters (temperature, holding time, and solid/liquid ratio). This observation was also in close agreement with the examinations by the silicon analysis, scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. The adsorption kinetics and the adsorption isotherm of methylene blue onto the resulting clay adsorbent can be well described by a pseudo-second-order reaction model and the Freundlich model, respectively.Effect of HF concentration on BET surface areas of modified diatomaceous earths prepared at the temperatures 60 and 80 °C, holding time 0.5 h, and solid/liquid ratio of 5 g/100 ml.
Keywords: Diatomaceous earth; Chemical modification; Hydrofluoric acid; Characterization; Adsorption;

Pressure dependence of the contact angle in a CO2–H2O–coal system by Nikolai Siemons; Hans Bruining; Hein Castelijns; Karl-Heinz Wolf (755-761).
Carbon dioxide injection into coal layers serves the dual purpose to enhance coal bed methane production (ECBM) and to store CO2. The efficiency of this process is expected to be much higher if water is the non-wetting phase in the coal–water–gas system. Therefore, contact angles in the coal–water–CO2 system have been measured using the captive bubble technique in the pressure range between atmospheric pressure and 141 bar at a temperature of 45 °C. At atmospheric pressure the contact angle of a shrinking CO2 droplet increases with time, but stays below 90°. At higher pressures (>2.6 bar) the contact angle increases beyond 90°. The pressure dependence of the contact can be represented by θ = ( 111 ° ± 10.5 ° ) + ( 0.17 ± 0.14 ) P   [bar] . The exceptional behavior at atmospheric pressure is possibly related to the stability of water patches on the coal surface. It is concluded that water is the non-wetting phase in this coal–water–CO2 system.Contact angles in the coal–water–CO2 system have been measured using the captive bubble technique between 1 and 141 bar at 45 °C. The pressure dependence of the contact can be represented by θ = ( 111 ° ± 10.5 ° ) + ( 0.17 ± 0.14 ) P   [bar] .
Keywords: Wetting properties; Water–CO2–coal system; High pressure; Contact angle;

Cusp at the three-fluid contact line in a cylindrical pore by M.I.J. van Dijke; K.S. Sorbie (762-771).
In a cylindrical pore of arbitrary wettability, we analyse the existence of a three-fluid contact line connecting the fluid–fluid interfaces between two bulk phases and the third phase contained in a cusp near the pore wall. This analysis is supported by the very similar, but simpler, analysis for a constriction between parallel plates. From the force balance at the contact line and the equations for the interface curvatures we derive expressions for the cusp height and for the capillary entry pressure related to piston-like displacement between the two bulk phases. The latter is independent of the existence of a cusp and its phase pressure. Based on some realistic assumptions, of which the most important is that a cusp grows continuously from the onset when its phase pressure is increased, we analyse under which conditions a cusp can exist, and, when it exists, what its behaviour is as a function of the cusp phase pressure. We find a simple criterion involving (two ratios of) the three interfacial tensions and two of the three contact angles, which determines whether the three-fluid contact line and, consequently, a cusp exists. The range of contact angles, as well as the size of the cusp increases, when the cusp phase is close to spreading. Not only cusps of the wetting phase can occur, but also of the intermediate-wetting phase. Numerical examples are presented to illustrate the range of behaviour of the cusps.Analysis of contact line connecting fluid–fluid interfaces between two bulk phases and third phase contained in cusp, balanced by interfacial tensions σ i j , in cylindrical pore of arbitrary wettability.
Keywords: Three-fluid contact line; Cusp; Interfacial tension; Contact angle; Capillary entry pressure; Constant total curvature;

Contact angle hysteresis of a macroscopic droplet on a heterogeneous but flat substrate is studied using the interface displacement model. First, the apparent contact angle of a droplet on a heterogeneous surface under the condition of constant volume is considered. By assuming a cylindrical liquid–vapor surface (meniscus) and minimizing the total free energy, we derive an equation for the apparent contact angle, which is similar but different from the well-known Cassie's law. Next, using this modified Cassie's law as a guide to predict the behavior of a droplet on a heterogeneous striped surface, we examine several scenarios of contact angle hysteresis using a periodically striped surface model. By changing the volume of the droplet, we predict a sudden jump of the droplet edge, and a continuous change of the apparent contact angle at the edge of two stripes. Our results suggest that as drop volume is increased (advancing contact lines), the predominant drop configuration observed is the one whose contact angle is large; whereas, decreasing drop volume from a large value (receding contact lines) yields drop configuration that predominantly exhibit the smaller contact angle.Contact angle hysteresis of a macroscopic cylindrical drops on a model heterogeneous striped surface is studied using the interface displacement model.
Keywords: Contact angle hysteresis; Cassie's law; Striped surface;

Water mass transfer in W/O emulsions by Marina Yu. Koroleva; Evgeny V. Yurtov (778-784).
Water transportation through the oil phase in W/O emulsions and in W1/O/W2 systems (W/O emulsion in contact with water) was examined. Substance diffusion through interfaces led to interface instability and spontaneous emulsification which caused nanodispersion formation. The photomicrographs of Pt/C replicas of emulsions showed the presence in the continuous oil phase a lot of nanodispersion droplets with a diameter in the range 17–25 nm. Diffusion coefficient (D) of water calculated on the base of Lifshiz–Slezov–Wagner (LSW) equation was about 15 times lower than the coefficients of molecular diffusion. Since such emulsions were extremely unstable toward coalescence, the growth of water droplets took place through as Ostwald ripening as coalescence. In three-phase W1/O/W2 systems diffusion of water, Rhodamine C, and ethanol was studied. D calculated on the base of the equation of nonstationary diffusion were approximately 1000 times lower than molecular ones. It was assumed, that nanodispersion droplets were more likely water carriers in investigated W/O emulsions stabilized by sorbitan monooleate.
Keywords: Ostwald ripening; W/O emulsion;

Stability of water/crude oil emulsions based on interfacial dilatational rheology by Christophe Dicharry; David Arla; Anne Sinquin; Alain Graciaa; Patrick Bouriat (785-791).
The dilatational viscoelasticity behaviors of water/oil interfaces formed with a crude oil and its distilled fractions diluted in cyclohexane were investigated by means of an oscillating drop tensiometer. The rheological study of the w/o interfaces at different frequencies has shown that the stable w/o emulsions systematically correspond to interfaces which present the rheological characteristics of a 2D gel near its gelation point. The stability of emulsions was found to increase with both the gel strength and the glass transition temperature of the gel. As expected, the indigenous natural surfactants responsible for the formation of the interfacial critical gel have been identified as the heaviest amphiphilic components present in the crude oil; i.e., asphaltenes and resins. Nevertheless, we have shown that such a gel can also form in the absence of asphaltene in the oil phase.
Keywords: Water-in-oil emulsion; Emulsion stability; Interfacial dilatational rheology; Oscillating pendant drop tensiometer; Gel; Asphaltenes; Resins;

Three fragrances, phenethylalcohol, benzaldehyde, and limonene (that differ in their polarity), were solubilized in lamellar liquid crystal using the polyethylene oxide–polypropylene oxide–polyethylene oxide, (EO27PO61EO27), P104 triblock copolymer, and water. The interlayer spacing of the lamellar liquid crystal were established using small angle X-ray scattering (SAXS). The SAXS data are used to calculate the interfacial area per polyethylene oxide (PEO) block and to determine the location of each fragrance in the association structure. The results show the presence of phenethylalcohol at the interface while part of benzaldehyde contributing to the interface and the other part being located inside the polar/apolar domains. The third fragrance, limonene, did not participate in the formation of the interface and is located inside the apolar domain.Phenethylalcohol is present at the interface. Part of the benzaldehyde contributes to the interface while the other part is located inside the polar/apolar domains. Limonene is not located at the interface but rather inside the nonpolar part.
Keywords: Fragrance; Block copolymer; Solubilization;

Interaction of cationic surfactants with carboxymethylcellulose in aqueous media by Jitendra Mata; Jaykumar Patel; Nirmesh Jain; Gautam Ghosh; P. Bahadur (797-804).
We have examined the polymer–surfactant interaction in mixed solutions of the cationic surfactants, i.e., dodecyltrimethylammonium chloride, dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, tetradecyltriphenylphosphonium bromide, and tetradecylpyridinium bromide and a semiflexible anionic polyelectrolyte carboxymethylcellulose in water and aqueous salt solutions by various techniques: tensiometry, viscosimetry or ion-selective electrode method, and dynamic light scattering. We have investigated the effect of varying surfactant chain length, head group size, counterion, and ionic strength on the critical aggregation concentration (CAC) of mixed polymer surfactant systems and the collapse of the polymer molecule under different solution conditions. The CAC decreases with increasing alkyl chain length. Above a certain surfactant concentration, mixed aggregates start growing until their macroscopic phase separation. The growth is more rapid with greater surfactant tail length and with increasing head group size. This is attributed in both cases to the increasing hydrophobic interaction between polymer and surfactant. Among surfactants with monovalent halide counterions, iodide induces the strongest binding, reflected by the onset of growth of the mixed aggregates at low surfactant concentration. This is perhaps related to the decreasing hydration of the counterion from chloride to iodide. The surfactant concentration at which the viscosity of the solution starts to decrease sharply is smaller than the CAC, and probably reflects polymer chain shrinkage due to noncooperative binding.
Keywords: Carboxymethylcellulose; Tensiometry; Noncooperative binding;

Sorbitan trioleate (Span 85) modified with Cibacron Blue F-3GA (CB) was used as an affinity surfactant (CB-Span 85) to form affinity-based reversed micelles in n-hexane. It was found that the addition of hexanol to the reversed micellar system resulted in a significant increase in water content and hydrodynamic radius of the affinity-based reversed micelles. Moreover, the reversed micelles with hexanol revealed broader aggregation number distribution and larger average aggregation number than the reversed micelles without hexanol addition. This is considered to be due to the decreases in the micellar curvature and rigidity of the micellar interfacial layer and the increase in the micellar interfacial fluidity. Consequently, the solubilization capacity of lysozyme increased about 70% in the reversed micellar solution with 3 vol% hexanol. On the other hand, the capacity of BSA was only 30% increased under the same conditions due to its larger molecular size than lysozyme. Kinetic analysis revealed that the increase in the micellar interfacial fluidity in the presence of hexanol resulted in faster release of lysozyme from the micelles, thus leading to an increase of the overall volumetric mass transfer coefficient in the back extraction.
Keywords: Affinity-based reversed micelles; Span 85; Cibacron Blue F-3GA; Water content; Hydrodynamic radius; Solubilization; Proteins;

Microstructure and rheological properties of liquid crystallines formed in Brij 97/water/IPM system by Zhongni Wang; Zhaoyu Diao; Feng Liu; Ganzuo Li; Gaoyong Zhang (813-818).
The phase diagram of Brij 97/water/IPM systems was determined at 25 °C. Rich liquid crystalline phases including L α , H 1 , and cubic Fd 3 m phases were identified by means of small angle X-ray scattering (SAXS). Microstructure transitions of liquid crystals with changes in surfactant concentration and oil content are explained qualitatively by the surfactant packing parameter ( v L / a S l c ). Dynamic rheological results indicate that all three kinds of liquid crystals investigated show high elasticity. The lamellar, L α , phases formed in Brij 97/water with two different oils, oleic acid and geraniol, were also studied in comparison with those of Brij 97/water/IPM systems. The strength of the network of lamellar phases formed in Brij 97/water/oleic acid and Brij 97/water/geraniol systems are appreciably stronger than for Brij 97/water/IPM systems, indicated by the smaller area of surfactant molecules at the interface and the higher moduli ( G ′ and G ″ ).Phase diagram for Brij 97/IPM/water system at 25 °C.
Keywords: Brij 97 nonionic surfactant; Liquid crystals; SAXS; Rheology;

Microelectromechanical systems (MEMS) employing spatially and/or temporally nonuniform electric fields have been extensively employed to control the motion of suspended particles or fluid flow. Design and control of microelectromechanical processes require accurate calculations of the electric field distribution under varying electrolyte conditions. Polarization of electrodes under the application of an oscillating voltage difference produces dynamic electrical double layers. The capacitive nature of the double layers significantly inhibits the penetration of the electric field through the double layer and into the surrounding bulk electrolyte at low frequencies. This paper quantitatively discusses the effect of electrode impedance on the electric field distribution as a function of field frequency, electrolyte composition, and electrode zeta potential in microelectrode systems. The design principles for the electrode geometry and configuration are also discussed in terms of their effects on the electric field magnitude and nonuniformity.This paper quantitatively discusses the effect of electrode impedance and electrode geometry and configuration on the electric field distribution in microelectrode systems.
Keywords: MEMS; Electrode impedance; Microelectrode arrays; AC electric field;

Eddies in a bottleneck: An arbitrary Debye length theory for capillary electroosmosis by Stella Y. Park; Christopher J. Russo; Daniel Branton; Howard A. Stone (832-839).
Using an applied electrical field to drive fluid flows becomes desirable as channels become smaller. Although most discussions of electroosmosis treat the case of thin Debye layers, here electroosmotic flow (EOF) through a constricted cylinder is presented for arbitrary Debye lengths ( κ −1 ) using a long wavelength perturbation of the cylinder radius. The analysis uses the approximation of small potentials. The varying diameter of the cylinder produces radially and axially varying effective electric fields, as well as an induced pressure gradient. We predict the existence of eddies for certain constricted geometries and propose the possibility of electrokinetic trapping in these regions. We also present a leading-order criterion which predicts central eddies in very narrow constrictions at the scale of the Debye length. Eddies can be found both in the center of the channel and along the perimeter, and the presence of the eddies is a consequence of the induced pressure gradient that accompanies electrically driven flow into a narrow constriction.Schematic of an axisymmetric cylinder with radial shape variation viewed as a cross section along the z-axis. The “perimeter” eddy paths—discussed in Section 3—are mapped out in gray with the direction of the eddies indicated by the curved arrows. The larger arrows indicate the overall direction of EOF. The perturbation wavelength is L and the invariant radius of the channel away from the constriction region is a 0 .
Keywords: Electroosmosis; Geometric variation; Eddy formation; Perturbation method; Recirculating flow; Shape variation;

We consider the 1-D Cahn–Hilliard equation with the order parameter v and derive an equation for a modified order parameter g such that g ″ = v ‘ . The new equation allows for separation of variables. This yields exact solutions for v expressed in terms of generalized hypergeometric functions. These solutions have an infinite gradient at their zeros and the first three derivatives of zero at their extrema. The amplitude of these patterns decreases as the inverse square root of time. It is suggested that the phenomenon of compartmentalization of evolving structures typically observed in evolutionary models of the Cahn–Hilliard type is a manifestation of relaxation patterns similar to those derived in this paper.For the Cahn–Hilliard equation, new exact solutions are derived. They have an infinite gradient at their zeros and the first three derivatives of zero at their extrema. Their amplitude decreases as the inverse square root of time.
Keywords: Nonlinear dynamics; Surface transport; Cahn–Hilliard;

A complementarity for extended Langmuir method by Qingdao Wang; Genxiang Luo; Haoping Wang; Chuangye Hou; Jun Jin (845-848).
The interaction free energy per unit area between parallel flat plates with high surface potential in the case of constant surface potential is again presented. It is complementarity for extended Langmuir method [G. Luo, H. Wang, J. Jin, Langmuir 17 (2001) 2167 and G. Luo, R. Feng, J. Jin, H. Wang, J. Colloid Interface Sci. 241 (2001) 81]. These approximate expressions work quite well for all values of the surface potentials so as the plates separations are small.
Keywords: Double layer interaction; Poisson–Boltzmann equation; Plate particles;

by Arthur Hubbard (849).