Journal of Colloid And Interface Science (v.298, #2)


Fe3O4 and γ-Fe2O3 nanoparticles for the adsorption of Co2+ from aqueous solution by Abdusalam Uheida; German Salazar-Alvarez; Eva Björkman; Zhang Yu; Mamoun Muhammed (501-507).
The adsorption of Co2+ ions from nitrate solutions using iron oxide nanoparticles of magnetite (Fe3O4) and maghemite (γ-Fe2O3) has been studied. The adsorption of Co2+ ions on the surface of the particles was investigated under different conditions of oxide content, contact time, solution pH, and initial Co2+ ion concentration. It has been found that the equilibrium can be attained in less than 5 min. The maximum loading capacity of Fe3O4 and γ-Fe2O3 nanoparticles is 5.8 × 10 −5 and 3.7 × 10 −5   mol m −2 , respectively, which are much higher than the previously studied, iron oxides and conventional ion exchange resins. Co2+ ions were also recovered by dilute nitric acid from the loaded γ-Fe2O3 and Fe3O4 with an efficiency of 86 and 30%, respectively. That has been explained by the different mechanisms by including both the surface and structural loadings of Co2+ ions. The surface adsorption of Co2+ on Fe3O4 and γ-Fe2O3 nanoparticles has been found to have the same mechanism of ion exchange reaction between Co2+ in the solution and proton bonded on the particle surface. The conditional equilibrium constants of surface adsorption of Co2+ on Fe3O4 and γ-Fe2O3 nanoparticles have been determined to be log K = − 3.3 ± 0.3 and − 3.1 ± 0.2 , respectively. The structural loading of Co2+ ions into Fe3O4 lattice has been found to be the ion exchange reaction between Co2+ and Fe2+ while that into γ-Fe2O3 lattice to fill its vacancy. The effect of temperature on the adsorption of Co2+ was also investigated, and the value of enthalpy change was determined to be 19 kJ mol−1.
Keywords: Adsorption; Magnetite; Maghemite; Cobalt(II); Nanoparticles;

Generation of nanostructures of mica supported lysozyme molecules in aqueous solution by atomic force microscopy by Frank Leisten; Matthias Wiechmann; Oliver Enders; Hans-Albert Kolb (508-514).
Nanostructures of lysozyme molecules adsorbed to mica were generated by the tip of an atomic force microscope in contact, tapping, and force-distance mode in aqueous solution. In contact mode at high ionic strength and adjusted lysozyme concentration a monolayer of defined pattern and orientation could be formed by the scan process of the tip. A lysozyme monolayer with minimal pattern size of about 60 nm was achieved by line scan. At larger loading forces besides a monolayer also 3D-aggregates of lysozyme molecules could be generated. In force-distance mode the volume of 3D-aggregates grows with increasing generation time, lysozyme concentration in the bulk phase, loading force, and frequency of up- and down-movement of the substrate toward the fixed cantilever. In tapping mode 3D-aggregates could be generated as well. It is postulated that reduction of electrostatic interaction between the oppositely charged lysozyme molecules and mica surface by sufficient high ionic strength is essential for monolayer formation. It is discussed that for the underlying mechanism of monolayer generation in contact mode lysozyme molecules of the bulk phase adsorb to the tip, become pulled off and attach to the mica surface by the scan process of the tip.
Keywords: Nanostructures; Lysozyme; Mica; AFM;

Kinetic and calorimetric study of the adsorption of dyes on mesoporous activated carbon prepared from coconut coir dust by Jeremias de Souza Macedo; Nivan Bezerra da Costa Júnior; Luis Eduardo Almeida; Eunice Fragoso da Silva Vieira; Antonio Reinaldo Cestari; Iara de Fátima Gimenez; Neftali Lênin Villarreal Carreño; Ledjane Silva Barreto (515-522).
Mesoporous activated carbon has been prepared from coconut coir dust as support for adsorption of some model dye molecules from aqueous solutions. The methylene blue (MB) and remazol yellow (RY) molecules were chosen for study of the adsorption capacity of cationic and anionic dyes onto prepared activated carbon. The adsorption kinetics was studied with the Lagergren first- and pseudo-second-order kinetic models as well as the intraparticle diffusion model. The results for both dyes suggested a multimechanism sorption process. The adsorption mechanisms in the systems dyes/AC follow pseudo-second-order kinetics with a significant contribution of intraparticle diffusion. The samples simultaneously present acidic and basic sites able to act as anchoring sites for basic and acidic dyes, respectively. Calorimetric studies reveal that dyes/AC interaction forces are correlated with the pH of the solution, which can be related to the charge distribution on the AC surface. These AC samples also exhibited very short equilibrium times for the adsorption of both dyes, which is an economically favorable requisite for the activated carbon described in this work, in addition to the local abundance of the raw material.Kinetic and calorimetric studies of MB and RY adsorption onto activated carbon prepared from waste material showed that the process follows a pseudo-second-order kinetics with contribution of intraparticle diffusion.
Keywords: Activated carbon; Coir dust; Porosity; Adsorption kinetics; Heat of adsorption;

Equilibrium and breakthrough adsorptions on activated carbon fibers (ACF) were conducted for CO2 and CH4 gas mixtures and the selective separation of CO2 was demonstrated. An electric swing adsorption process (ESA) was exploited to effect the rapid desorption of adsorbed gas at atmospheric pressure. Also, the relationship between the electrical behavior and desorption characteristics of ACF is discussed. In a single component adsorption experiment, the amount of adsorbed CO2 reached up to 40 mg/g-ACF, twice as much as that of adsorbed CH4. Therefore, the separation factor, defined as the ratio of adsorbed CO2 to adsorbed CH4, was 2.0. Multicomponent experiments showed a higher separation factor of 5.2, owing to a roll-up phenomenon. The temperature increase is not linearly proportionate to the power input, while the passage of higher electrical voltage (30 V) caused the ACF temperature to exceed 200 °C within 30 s. CO2 desorption at low voltage was well accomplished by heating the ACF to temperatures <60 °C. An ACF adsorption bed regenerated with ESA showed a constant regeneration efficiency of over 85% with a regular breakthrough curve. The ESA method increased desorption efficiency by over 20%, compared with the vacuum method.An electric swing adsorption process (ESA) showed a higher separation factor of 5.2 and a constant regeneration efficiency over 85% with a regular breakthrough curve at atmospheric. The ESA method increased desorption efficiency by over 20%, compared with the vacuum method.
Keywords: Activated carbon fibers; Adsorption; Gas separation; Regeneration; Electrical properties;

Action mechanism of water soluble ethanol on phospholipid monolayers using a quartz crystal oscillator by Yasushi Yamamoto; Keijiro Taga; Tadayoshi Yoshida; Hiroshi Kamaya; Issaku Ueda (529-534).
Interaction between phospholipid monolayers (dihexadecyl phosphate: DHP, dipalmitoyl phosphatidyl choline: DPPC) and water soluble ethanol has been studied using quartz crystal microbalance (QCM) method and quartz crystal impedance (QCI) method. The quartz crystal oscillator was attached horizontally on the DHP and DPPC monolayers that were formed on the water surface. At low concentration, increased ethanol concentration decreased the frequency for QCM and increased the resistance for QCI. Both frequency and resistance approached asymptotically to a saturation value. A further increase in ethanol concentration induced a sudden and discontinuous linear change (a decrease in frequency and an increase in resistance). Based on these results, we propose the following action mechanism of ethanol on phospholipid monolayers: at low concentration, the ethanol hydrates adsorb into the monolayer/water interface and saturate on the interface. The monolayer viscosity also increases with the adsorption of hydrates. A further increase in concentration causes multilayer formation of hydrates and/or penetration of hydrates into the monolayer core. The viscosity of the interfacial layer (monolayer and interfacial structured water) changes dramatically according to the action of ethanol hydrates.Ethanol-concentration dependent behavior of resistance (ΔR) for quartz crystal oscillator in contact with two monolayers after adding various ethanol concentrations. Circle: DHP, diamond: DPPC.
Keywords: Quartz crystal microbalance; Quartz crystal impedance; Phospholipid monolayer; Ethanol hydrate; Monolayer/water interface; Interfacial fluidity; Monolayer viscosity; Interfacial structured water; Anesthesia mechanism;

Preparation of cerium-loaded Y-zeolites for removal of organic sulfur compounds from hydrodesulfurizated gasoline and diesel oil by Mei Xue; Ramesh Chitrakar; Kohji Sakane; Takahiro Hirotsu; Kenta Ooi; Yuji Yoshimura; Makoto Toba; Qi Feng (535-542).
Ce(IV)-loaded Y-zeolites (CeY) were prepared for selective removal of the trace amount of organic sulfur compounds from hydrodesulfurization (HDS)-treated diesel oil. The CeY samples can be obtained from NH4–Y-zeolite (NH4Y) using liquid-phase ion-exchange and solid-state ion-exchange methods. The ion-exchange reactions, structures, and selective adsorptions of organic sulfur compounds of the CeY samples were investigated using XRD, IR, XPS, TEM, and GC sulfur analyzer. The organic sulfur compound uptakes strongly depend on the amount and the valency of Ce in the zeolite structure. Ce(IV) shows much higher adsorptive ability than Ce(III). A CeY–S sample prepared by solid-state ion-exchange reaction of NH4Y and Ce(NO3)3 with Ce/NH4 mole ratio of 0.63 at 250 °C showed a maximum sulfur uptake from a model solution of HDS-treated gasoline containing thiophene [ S = 5 ppm (ppm = mg/L)]. A desulfurization from a HDS-treated diesel oil containing organic sulfur compounds ( S = 1.87 ppm ) and H2S ( S = 0.73 ppm ) was investigated with a combination of the CeY–S and a CuO adsorbent for removal of H2S by a batch method. The sulfur content was reduced to below 0.01 ppm for the first time. This method provides a promising desulfurization process to prepare a clean fuel for fuel cells.The CeY–S samples prepared by solid-state ion-exchange reaction shows high sulfur uptakes. We propose a mechanism for the reaction system. When Ce/NH4 < 0.63, most of Ce(IV) species is inserted into the zeolite phase. When Ce/NH4 > 0.63, a parts of Ce species can be inserted into the zeolite phase, and the residual Ce species change to CeO2 phase.
Keywords: Thiophene; Cerium; Zeolite; Sulfur removal; Solid-state reaction; Hydrodesulfurization; Diesel oil; Organic sulfur;

In situ sensing of metal ion adsorption to a thiolated surface using surface plasmon resonance spectroscopy by Jungwoo Moon; Taewook Kang; Seogil Oh; Surin Hong; Jongheop Yi (543-549).
The kinetics of the adsorption of metal ions onto a thiolated surface and the selective and quantitative sensing of metal ions were explored using surface plasmon resonance (SPR) spectroscopy. The target metal ion was an aqueous solution of Pt2+ and a thin-gold-film-coated glass substrate was modified with 1 , 6 -hexanedithiol (HDT) as a selective sensing layer. SPR spectroscopy was used to examine the kinetics of metal ion adsorption by means of the change in SPR angle. The selectivity of the thiolated surface for Pt2+ over other divalent metal ions such as Cu2+, Ni2+, and Cd2+ was evident by the time-resolved SPR measurement. SPR angle shift, Δ θ SPR , was found to increase logarithmically with increasing concentration of Pt2+ in the range of 1.0 × 10 −5 – 1.0 mM . The rate of Pt2+ adsorption on HDT observed at both 0.1 and 1 mM Pt2+ accelerates until the surface coverage reaches approximately 17%, after which the adsorption profile follows Langmuirian behavior with the surface coverage. The experimental data indicated that heavy metal ions were adsorbed to the hydrophobic thiolated surface by a cooperative mechanism. A mixed self-assembled monolayer (SAM) composed of HDT and 11-mercaptoundecanoic acid was used to reduce the hydrophobicity of the thiol-functionalized surface. The addition of hydrophilic groups to the surface enhanced the rate of adsorption of Pt2+ onto the surface. The findings show that the adsorption of metal ions is strongly dependent upon the hydrophilicity/hydrophobicity of the surface and that the technique represents an easy method for analyzing the adsorption of metal ions to a functionalized surface by combining SPR spectroscopy with a SAM modification.The kinetics of the adsorption of metal ions to a thiolated surface and the selective and quantitative sensing of metal ions was explored using surface plasmon resonance (SPR) spectroscopy. The target metal ion was Pt2+ in an aqueous solution and a thin gold film coated on glass substrate was modified with 1,6-hexanedithiol (HDT) as a selective sensing layer. SPR spectroscopy was used to investigate the kinetics of metal ion adsorption by means of the change in SPR angle. Experimental data indicated that metal ions are adsorbed to a hydrophobic thiolated surface by a cooperative mechanism. This technique represents a facile method for analyzing the adsorption of metal ions onto a functionalized surface by combining SPR spectroscopy with a SAM modification.
Keywords: SPR; Metal ions; Adsorption; Kinetics; Mixed SAM;

The adsorption of sodium poly(4-styrene sulfonate) on oppositely charged β-FeOOH particles is studied by electrooptics. The focus of this paper is on the release of condensed counterions from adsorbed polyelectrolyte upon surface charge overcompensation. The fraction of condensed Na+ counterions on the adsorbed polyion surface is estimated according to the theory of Sens and Joanny and it is compared with the fraction of condensed counterions on nonadsorbed polyelectrolyte. The relaxation frequency of the electrooptical effect from the polymer-coated particle is found to depend on the polyelectrolyte molecular weight. This is attributed to polarization of the layer from condensed counterions on the polyion surface, being responsible for creation of the effect from particles covered with highly charged polyelectrolyte. The number of the adsorbed chains is calculated also assuming counterion condensation on the adsorbed polyelectrolyte and semiquantative agreement is found with the result obtained from the condensed counterion polarizability of the polymer-coated particle. Our findings are in line with theoretical predictions that the fraction of condensed counterions remains unchanged due to the adsorption of highly charged polyelectrolyte onto weakly charged substrate.
Keywords: Polyelectrolyte adsorption; Condensation of counterions; Counterion release; Colloid/polyelectrolyte complexation; Overcharging of colloidal particles;

Sorption of selenite ions on hematite by M. Duc; G. Lefèvre; M. Fédoroff (556-563).
The sorption of selenite from aqueous solutions onto hematite was investigated as a function of pH (2–12), ionic strength (0.01–0.1 M), and concentration of selenium ( 10 −7 – 10 −2   M ). The sorption may proceed according to two processes: surface complexation, followed by the precipitation of ferric selenite starting at approximate [ Se ] = 4 × 10 −4   M (surface coverage > ca. 2 at nm−2). The sorption isotherms have been fitted by a Tempkin equation. A surface complexation model (2-pK/Constant Capacitance Model) was used to fit the sorption data. The nature of the surface species of selenite cannot be determined by modeling since monodentate >FeO―Se(O)O or >FeO―Se(O)OH and bidentate (>FeO)2SeO surface complexes are both able to fit the experimental data. The reversibility and kinetics of sorption were also studied. The affinity of selenite ions toward hematite, expressed as the distribution coefficient with respect to the surface area ( K D in L m−2), was compared with results published for other ferric oxides (goethite and amorphous ferric oxide). It was found that the reactivity toward selenite is similar, contrary to acid–base properties which depend on the nature of the oxide and its level of purity.Sorption of selenite ions modeled by a bidentate complex.
Keywords: Selenium; Iron oxide; Isotherm; Surface complex;

The pull-off force required to separate two elastic bodies in adhesive binding depends on the surface shapes of the corresponding binding regions on the two bodies. Given a fixed binding area A, the optimal shapes are those which give the maximum pull-off force σ th A where σ th is the theoretical strength of interactive forces between the two solids. Here we study closed form solutions to the optimal shapes for adhesive binding over a small circular region where slip is allowed whenever shear stress along the contact interface exceeds a critical value.The pull-off force required to separate two elastic bodies in adhesive binding depends on the surface shapes of the corresponding binding regions on the two bodies. Here we study closed form solutions of optimal surface shapes that lead to the maximum pull-off force adhesive binding over a fixed circular area which is divided into a slipping ( a ⩽ r ⩽ R ) and nonslipping ( r < a ) region according to the shear strength of the contact interface.
Keywords: Adhesion; Binding; Contact mechanics; Slip; Intermolecular adhesion; Friction; Hankel transform;

Effect of aqueous acetic, oxalic, and carbonic acids on the adsorption of europium(III) onto α-alumina by Cyrille Alliot; Lionel Bion; Florence Mercier; Pierre Toulhoat (573-581).
Chemical retention, i.e., partition of the element between aqueous solution and mineral surface, is a key phenomenon for assessing the safety of possible nuclear waste disposal. For this purpose, the sorption of Eu(III) onto a model mineral—α-alumina—is studied here, including the effects of groundwater chemistry: pH and concentrations of small organic and inorganic ligands (acetate, oxalate, and carbonate anions). This work presents some experimental evidence for a synergic mechanism of sorption of europium–ligand complexes onto the alumina. Only cationic complexes were necessary to consider to model experimental results. Using the ion-exchange theory (IET) and a corresponding restricted set of parameters—exchange capacities and thermodynamic equilibrium constants—the whole set of sorption experiments of Eu(III) cationic species onto the α-alumina was modeled under various chemical conditions.The synergic effects of complexing organic acids on europium(III) sorption onto α-alumina.
Keywords: Alumina; Europium(III); Oxalate; Acetate; Carbonate; Sorption; Synergic; Ion-exchange theory;

Many mine soils are chemically, physically, and biologically unstable and deficient. They are sometimes amended with sewage sludge and ashes but often contain heavy metals that increase the already high mine soils' heavy metal contents. Cd, Cr, Cu, Ni, Pb, and Zn in mutual competition were added to five mine soils (Galicia, Spain). Soil capacities for heavy metal sorption and retention were determined by means of distribution coefficients and selectivity sequences among metals. Influence of soil characteristics on sorption and retention was also examined. Retention selectivity sequences indicate that, in most of the soils, Pb is the preferred retained metal, followed by Cr. The last metals in these sequences are Ni, Cd, and Zn. Soil organic matter content plays a fundamental role in control of Pb sorption. Gibbsite, goethite, and mica influence Cr retention. Soil organic matter, oxides, and chlorite contents are correlated with K d ∑ sp medium . Heavy metals are weakly adsorbed by soils and then desorbed in high amounts. To recover these soils it is necessary to avoid the use of residues or ashes that contain heavy metals due to their low heavy metal retention capacity.Mine soils from Touro (Galicia, Spain) amended with sewage sludge and ashes containing heavy metals.
Keywords: Mine soils; Heavy metals; Sorption–desorption; Selectivity sequences;

A phenomenological multilayer adsorption model for a well-dispersed, homogeneous, nonporous adsorbent and a molecular adsorbate is presented. The model provides explicit kinetic expressions associating the adsorbed amounts to the fraction of the surface occupied and reduces to the first- and second-order adsorption models for special cases. Parameters of the model are a pair of true rate constants related to the adsorbate–adsorbent and adsorbate–surface adsorbate affinities. A general graphical procedure and analytical equations for special cases are provided to estimate the rate constants from kinetic adsorption data. Data from the adsorption of sodium stearate onto α-alumina from water were used to test the model. The predicted values of the rate constants suggested that the stearate was distributed homogeneously on the alumina surface and essentially adsorbed as a monolayer before starting to form the second layer.A phenomenological multilayer adsorption model for well-dispersed, homegeneous, nonporous adsorbent–molecular adsorbate system is proposed. It provides explicit kinetic expressions associating the adsorbed amounts to fractional surface coverage.
Keywords: Adsorption; Modeling; Kinetics; Multilayer;

Phosphate adsorption on synthetic goethite and akaganeite by Ramesh Chitrakar; Satoko Tezuka; Akinari Sonoda; Kohji Sakane; Kenta Ooi; Takahiro Hirotsu (602-608).
Low crystalline iron hydroxides such as goethite (α-FeOOH) and akaganeite (β-FeOOH) were synthesized, and the selective adsorption of phosphate ions from phosphate-enriched seawater was examined. The results of the distribution coefficients ( K d ) of oxoanions in mixed anion solutions at pH 8 follow the selectivity order Cl, NO 3, SO2− 4  ≪ CO2− 3, HPO2− 4 for goethite, and Cl, CO2− 3  < NO 3  < SO2− 4≪ HPO2− 4 for akaganeite. In seawater, both adsorbents show high selectivity for phosphate ions despite the presence of large amounts of major cations and anions in seawater. The adsorption isotherms fitted better with the Freundlich equation and the maximum uptake of phosphate from phosphate-enriched seawater was 10 mg P/g at an equilibrium phosphate concentration of 0.3 mg P/L on both adsorbents. The phosphate adsorption/desorption cycles show that akaganeite is an excellent adsorbent even after 10 cycles and its chemical stability is good.Low crystalline goethite and akaganeite are selective toward phosphate ions in seawater.
Keywords: Goethite; Akaganeite; Phosphate; Seawater; Adsorption;

The effect of potassium, sodium, calcium, magnesium, and hydrogen cations on adsorption of guar gum onto quartz was investigated at natural pH. The role of the background ions was analyzed in terms of their water-structure making or breaking capabilities. In dilute solutions (0.01 mol/L) of structure-makers (NaCl, HCl, CaCl2, and MgCl2), the guar gum adsorption density did not change compared to the adsorption densities obtained in distilled water. Potassium, the only structure-breaking ion (chaotrope) among the tested cations, significantly enhanced guar gum adsorption. The results obtained in mixed electrolytes demonstrate that the strong structure-breaking properties of K+ overcome any contributions from weak structure making ions (kosmotropes), and guar gum adsorption remains at the levels observed in KCl alone. Only when strongly hydrated Mg2+ ions are mixed with KCl, the overall effect becomes additive and the influence of potassium is proportionally reduced by increasing concentrations of magnesium cations. In this approach, guar gum adsorption on quartz is viewed as a competition between polysaccharide and water molecules for silanol surface sites. The hydration of the quartz surface inhibits the adsorption process but the competition equilibrium, and hence polysaccharide adsorption, can be affected by the presence of chaotropes or kosmotropes.The adsorption of guar gum onto quartz is a function of the hydration of background cations.
Keywords: Guar gum; Quartz; Polymer adsorption; Ionic strength; Water structure;

The impact of Mn oxide coatings on Zn distribution by Thipnakarin Boonfueng; Lisa Axe; Ying Xu; Trevor A. Tyson (615-623).
Zinc sorption to hydrous manganese oxide (HMO)-coated clay was investigated macroscopically, kinetically, and spectroscopically. Adsorption edges and isotherms revealed that the affinity and capacity of the HMO-coated montmorillonite was greater than that of montmorillonite, and when normalized to the oxide present, the coatings behaved similarly to the discrete Mn oxide. Over two pH conditions, 5 and 6, a linear relationship was observed for the isotherms; further analysis with X-ray absorption spectroscopy (XAS) resulted in one type of sorption configuration as a function of loading and ionic strength at pH 5. However, at a surface loading of 10 −3   mol Zn g HMO - coated clay −1 when the pH increased from 5 to 7, the first shell distance decreased slightly, while the atoms and coordination numbers remained the same; this change may be attributed to an increase in electrostatic interactions. After a contact time of 4 months where an additional 60% of the sites become occupied, the slower sorption process was modeled as intraparticle surface diffusion. Best fit diffusivities ranged from 10−18 to 10 −17   cm 2 / s , where a slower process was observed for the coated surface as compared to the discrete oxide. Interestingly, the porosity of the Mn oxide coating appears to be influenced by the substrate during its growth, as its increase and shift to a smaller pore size distribution resulted in a diffusivity between that observed for discrete HMO and montmorillonite.Proposed Zn sorption configuration on hydrous manganese oxide (HMO) shows (a) tridentate corner-sharing octahedral coordination, and (b) the unit cell of HMO structure.
Keywords: Zn; Sorption; XAS; Manganese oxide; Montmorillonite; HMO-coated montmorillonite; Intraparticle surface diffusion;

Preparation of sodium oleate/layered double hydroxide composites with acid-resistant properties by Yoshikazu Kameshima; Hisako Yoshizaki; Akira Nakajima; Kiyoshi Okada (624-628).
Mg―Al―CO3 type layered double hydroxides (LDHs) with Mg/Al ratios ranging from 2 to 5 were synthesized by coprecipitation. Composites with sodium oleate/LDH were prepared by ion exchange and reconstruction of the LDH in sodium oleate solution. The amount of sodium oleate in the composites prepared by this reconstruction method was higher than that in samples prepared by the ion-exchange method. The basal spacings of the LDHs increased to 3.9 and 1.8 nm after synthesis of the composites, these spacings being in good agreement with models based on the assumption that the oleate ions are intercalated as bilayer and/or micelle structures, and as monolayers in the LDH interlayers, respectively. The number of sorbed oleate ions was higher than calculated from the anion-exchange capacities of the LDHs in most of the samples, increasing as the Mg/Al ratios of the LDHs were increased from 2 to 5. These results suggest that the oleate ions are present not only in the interlayers but also on the surfaces of the LDH particles. The acid-resistant properties of the composites were found to be much higher than for the pure LDHs. It is thus confirmed that the surfaces of the LDH particles in the composites are mostly covered with sorbed oleate ions and that the composites are good candidates as drug delivery materials.
Keywords: Layered double hydroxide; Sodium oleate; Composite; Acid-resistant properties;

The effect of inhomogeneous stickiness on polymer aggregation by Aisling M. Metcalfe; Serge Stoll; Adrian Burd (629-638).
The aggregation of polymers is important in the formation of marine aggregates and the vertical transport of material in the ocean. A polymer may be inhomogeneous along its length, with associating groups at some points along its length where bonds are more likely to form. In this paper we investigate the effects of inhomogeneous ‘stickiness’ along the polymer length. We describe the results of three-dimensional off-lattice simulations of polymer–polymer aggregation for four different types of polymer: polymers which are sticky along their entire length, polymers which are sticky at the ends only and two types of polymer which are slightly sticky along their entire length. We examine the mean radius of gyration and the fractal dimension of the resulting aggregates and the dynamics of aggregation. The slightly sticky polymers and the polymers which are sticky only at the ends form aggregates with a higher fractal dimension than the polymers which are sticky along their entire length. However, the mean radius of gyration of the aggregates formed by polymers which are sticky only at the ends is significantly larger than that of the aggregates formed from slightly sticky polymers. The aggregation dynamics are also different for the polymers which are sticky only at the ends compared to the slightly sticky polymers. A single ‘stickiness value’ is therefore likely to be inadequate to describe a polymer. We also examine the effect of polymer rigidity; it seems that the effect of inhomogeneous stickiness is greater for almost-straight polymers than for coiled chains.
Keywords: Polymer; Aggregation; Inhomogeneous stickiness; Fractal dimension; Modelling; Computer simulation;

Morphology control of poly(vinylidene fluoride) thin film made with electrospray by Ivo B. Rietveld; K. Kobayashi; H. Yamada; K. Matsushige (639-651).
Thin polymer films of poly(vinylidene fluoride) were prepared with electrospray. Effects of solvent, initial spray concentration, temperature, solution conductivity, and polymer size on the film morphology were studied with AFM. The two main factors controlling polymer film morphology are the droplet size of the spray and the viscosity of the solution at deposition. These factors determine the flow of the polymer-solvent mixture over the substrate, the density of the film, and its smoothness. The solvent is a key parameter of the entire process. It affects spray stability, polymer solubility, droplet size of the spray, and viscosity of the solution at deposition. Solvents with a low vapor pressure provide a wider window for optimization of other parameters and are therefore preferred over solvents with high vapor pressure. The viscosity at deposition is mainly controlled with the initial spray concentration, polymer size, temperature, and droplet size. The droplet size is best controlled by the conductivity of the solution and the flow rate of the spray.
Keywords: Poly(vinylidene fluoride); Thin film; Electrospray; Electrohydrodynamic atomization; Polymer; Morphology control; Electrospray deposition;

The Johnson–Kendall–Roberts (JKR) theory of elastic contact, extended to take viscoelastic effects into account, is used to evaluate work of adhesion and modulus of elastomeric films. In this paper, we present a comparison of five approaches to analyze quasi-static and dynamic JKR force curve data obtained using instrumented indentation. The load-displacement experiments were performed using a 200-μm radius borosilicate glass sphere against poly(dimethyl siloxane) (PDMS). By applying a small oscillation to the tip during indentation, dynamic stiffness vs load data were also obtained for frequencies between 25 and 160 Hz. Direct curve fitting as well as simplified 2- and 3-point analysis methods were used to compare modulus values obtained from load-displacement and stiffness-load data. Fit methods not requiring determination of the initial point of tip–sample contact (“zero” displacement) provided modulus values closest to those obtained by direct curve fitting. The dynamic stiffness-load data revealed a frequency dependent modulus; load-displacement measurements obtained simultaneously were consistent with the relaxed, or low-frequency, modulus of the PDMS sample. These experiments demonstrate that both the frequency dependent and relaxed modulus can be obtained from a single experiment.This paper demonstrates that dynamic force curves can provide both the relaxed and dynamic moduli of compliant polymers when analyzed using JKR theory modified to take viscoelastic effects into account.
Keywords: Nanoindentation; Force curve; Adhesion; Viscoelastic; JKR; PDMS; Dynamic modulus; Relaxed modulus; AFM; Polymer films;

Synthesis of highly monodisperse polystyrene microspheres via dispersion polymerization using an amphoteric initiator by Jeongwoo Lee; Jin Uk Ha; Soonja Choe; Chang-Soo Lee; Sang Eun Shim (663-671).
The highly monodisperse polystyrene (PS) microspheres were produced by dispersion polymerization using an amphoteric initiator, 2 , 2 ′ -azobis [N-(2-carboxyethyl)-2-2-methylpropionamidine] (VA-057). The polymerization characteristics were investigated and compared with conventional initiators, 2,2-azobis(isobutyronitrile) (AIBN) and benzoyl peroxide (BPO). The monodisperse PS microspheres having the coefficient of variation ( C v ) of diameter all less than 4% are obtained at very low stabilizer, poly(vinyl pyrrolidone) (PVP) concentrations of 1 and 2 wt%. It is found that the size dependence of the VA-057 system, D n ∝ [VA-057]0.267, is less sensitive than a conventional initiator system. When the same amount, 2 wt%, of AIBN, BPO, and VA-057 is used under the identical PVP concentration of 2 wt%, the D n / C v 's are 1.95/11.57, 1.47/22.44, and 2.08 μm/2.50%, respectively. The uniformity of particles was characterized employing an optical analyzer, Turbiscan. For the VA-057 system, the back scattering intensity is linearly reduced with time having a constant sedimentation rate of 48.98 μm/min throughout the settling process. The uniformity of PS particles in the VA-057 system stems from (1) the higher rate of polymerization in early stage of polymerization, followed by significantly faster reduction of the rate, and (2) good dispersion stability of primary particles. Therefore, it is found that the use of an amphoteric initiator, VA-057, is promising for producing monodisperse particles in dispersion polymerization.The highly monodisperse polystyrene (PS) microspheres were produced by dispersion polymerization using an amphoteric initiator, 2 , 2 ′ -azobis [N-(2-carboxyethyl)-2-2-methylpropionamidine] (VA-057) in alcoholic media.
Keywords: Colloids; Dispersion polymerization; Polystyrene; Amphoteric initiator; Microspheres;

To study the interaction between liposomes and proteins, intact liposomes were immobilized on a metal planar support by chemical binding and/or bioaffinity using a quartz crystal microbalance (QCM). A large decrease in the resonance frequency of quartz crystal was observed when the QCM, modified by a self-assembled monolayer (SAM) of carboxythiol, was added to liposome solutions. The stable chemical immobilization of intact liposomes onto SAM was judged according to the degree with which adsorbed mass depended on the prepared size of liposomes, as well as on the activation time of SAMs when amino-coupling was introduced, where the liposome coverage of electrodes was 69 ± 8 % in optimal conditions. When avidin–biotin binding was used on amino-coupling liposome layers, liposome immobilization finally reached 168% coverage of the electrode surface. Denatured protein was also successfully detected according to the change in the frequency of the liposome-immobilized QCM. The adsorbed mass of denatured carbonic anhydrase from bovine onto immobilized liposomes showed a characteristic peak at a concentration of guanidine hydrochloride that corresponded to a molten globule-like state of the protein, although the mass adsorbed onto deactivated SAM increased monotonously.The stable chemical immobilization of intact liposomes onto SAM was achieved. The adsorbed mass of denatured carbonic anhydrase from bovine onto immobilized liposomes showed a characteristic peak at a concentration of guanidine hydrochloride that corresponded to a molten globule-like state of the protein, although the mass adsorbed onto deactivated SAM increased monotonously.
Keywords: Immobilization of liposome; Amino-coupling; Avidin–biotin binding; Phospholipid membrane-protein interaction; Denatured protein; Quartz crystal microbalance;

Organic dye molecules as reducing agent for the synthesis of electroactive gold nanoplates by Jadab Sharma; Kunjukrishna P. Vijayamohanan (679-684).
Highly crystalline, hexagonal and triangular nanoplates of gold are synthesized in high yield by a new wet chemical method using multifunctional molecules, Bismarck brown R (BBR) and Bismarck brown Y (BBY). This method involves a simple approach by keeping a mixture of aqueous HAuCl4 solution and BBR/BBY solution in presence of poly(vinyl pyrrolidone) for 24 h. These nanostructures show unprecedented electrochemical properties exhibiting surface confinement effect. The UV–visible (UV–vis) spectrum shows certain distinct features with absorptions at 300, 400, and 650 nm extending up to the near infrared region. Selected area electron diffraction patterns of these nanoparticles show highly oriented (111) crystal facets. X-ray diffraction analysis also confirms the predominant orientation in the (111) crystal planes with lattice constant ∼4.07 Å of face-centered-cubic (fcc) gold. X-ray photoelectron (XP) and Fourier transform infrared (FTIR) spectroscopic analysis shows the presence of a fraction of reducing molecules as surface passivating agent either in the unreacted molecular state or as a mixture of reacted and unreacted product, which probably undergoes charge transfer with gold nanocrystals giving absorption at ∼300 nm.
Keywords: Gold nanoplates; Bismarck brown; Poly(vinyl pyrrolidone); Surface plasmon resonance; Cyclic voltammetry;

Fine tuning photoluminescence properties of CdSe nanoparticles by surface states modulation by Jie Zeng; Wei Lu; Xiaoping Wang; Bing Wang; Guanzhong Wang; J.G. Hou (685-688).
Fine control of the photoluminescence properties of CdSe nanoparticles (NPs) dispersed in CHCl3 is achieved by simple adjustment of the NPs concentration, and the wavelength of photoluminescence emission of CdSe NPs can be tuned within the nanometer accuracy. The mechanism of the process is proposed to be relevant to the modulation of the surface states of NPs by the concentration. This solution-based approach offers an attractive and complementary process to the conventional band gap engineering of semiconductor NPs with fine tunable optical properties.The process of HDA adsorbed on and desorbed from CdSe nanoparticles (NPs) in CHCl3 can modulate the amount of the surface states of NPs by the concentration, which can be used to fine tune the photoluminescence of CdSe NPs.
Keywords: Nanoparticles; Semiconductor; Surface states modulation; Optical properties;

Silver nanowires were synthesized by the hydrothermal route in aqueous solution of gemini surfactant 1,3-bis(cetyldimethylammonium) propane dibromide (16-3-16) at a relatively low temperature. The as-prepared silver nanowires were characterized by X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD), transmission electron microscope (TEM), electron diffraction (ED), and UV–vis absorption spectrum. The obtained silver nanowires are of high aspect ratios with an average diameter of ∼30 nm and length ranging from several to tens of micrometers.Silver nanowires were synthesized by the hydrothermal route in aqueous solution of gemini surfactant 1,3-bis(cetyldimethylammonium) propane dibromide (16-3-16) at a relatively low temperature. The obtained silver nanowires are of high aspect ratios with an average diameter of ∼30 nm and length ranging from several to tens of micrometers.
Keywords: Silver nanowires; Hydrothermal synthesis; Gemini surfactant;

Temperature effect on the stability of bentonite colloids in water by Sandra García-García; Mats Jonsson; Susanna Wold (694-705).
The stability of natural bentonite suspensions has been investigated as a function of temperature at pH 9 and ionic strength 10−3 M. The sedimentation rate of the particles is directly related to their stability. The sedimentation kinetics was determined by examining the variation of particle concentration in solution with time. The observed kinetics for sedimentation is discussed quantitatively in terms of the potential energy between particles. The ζ-potential of the particles was measured and the DLVO theory was used to calculate attractive and repulsive potentials. Experimental observations are consistent with DLVO model predictions and show that the stability of bentonite colloids increases with temperature. Differences with other colloidal systems can be attributed to the temperature dependence of the surface charge of bentonite particles.The stability of bentonite colloids was found to increase with increasing temperature.
Keywords: Bentonite colloids; DLVO theory; PCS; Zeta potential; Sedimentation;

Characterization of silica-coated tobacco mosaic virus by Elizabeth Royston; Sang-Yup Lee; James N. Culver; Michael T. Harris (706-712).
The deposition of silica on the surface of tobacco mosaic virus (TMV) is achieved at a higher pH (>7) as a means to enhance its usefulness as a template for the synthesis of nanostructures. Electron energy loss spectroscopy definitively shows the presence of a silica shell on the surface of the TMV while small angle X-ray scattering differentiates successfully between silica-coated TMV and silica particles in the presence of uncoated TMV. Importantly, coating reactions done in a 50% w/v methanol/water solution produce smaller silica nanostructures during the condensation of the hydrolysis intermediates, possibly aiding in obtaining uniform coating. Furthermore, TMV-templated silica coatings are found to enhance the stability of the virus particle in methanol at conditions that would ordinarily disrupt the assembled particle. Combined these findings demonstrate that TMV can function as an efficient template for the controlled deposition of silica at neutral pH.
Keywords: Tobacco mosaic virus; Silica; EELS; SAXS;

Direct-write fabrication of colloidal photonic crystal microarrays by ink-jet printing by Jungho Park; Jooho Moon; Hyunjung Shin; Dake Wang; Minseo Park (713-719).
An array of the colloidal photonic crystals was directly fabricated using an ink-jet printing. The colloidal ink droplets containing the monodispersed polystyrene latex particles were selectively deposited on a hydrophobic surface. Solvent evaporation from each ink droplet leads to a formation of microdome-shaped colloidal assembles of close-packed structures. Microspectroscopic analysis has confirmed that the individual assembly serves as a photonic crystal and its optical properties can be correlated with the microstructural features. Unlike other techniques of patterned growth of colloidal photonic crystal, the substrate does not need to be patterned first and no template is needed in the direct writing by the ink-jet printing. Using our strategy, we have rapidly produced the colloidal photonic crystal microarrays composed of different-sized spheres addressably patterned on the same substrate.An array of colloidal photonic crystal with was fabricated using an ink-jet printing. Colloidal crystals comprised of different-sized spheres were patterned on the same substrate, reflecting two different colors.
Keywords: Self-assembly; Colloid crystal; Ink-jet printing;

Selective separation of pyrite and galena from mixture of the two minerals was achieved through interaction with cells and metabolic products from a culture of Paenibacillus polymyxa. Adsorption of cells and metabolic products onto minerals and electrokinetic studies of minerals after interaction with cells and metabolic products were carried out to examine the resulting surface modification on the mineral surfaces. Flocculation and flotation techniques were successfully applied in the selective separation of minerals after bacterial interaction. The effect of varying conditions for production of extracellular polysaccharides and protein provided an insight into the possible mechanism involved in microbially induced flocculation and flotation of pyrite and galena.Selective separation of pyrite and galena from mixture of the two minerals was achieved through interaction with cells and metabolic products from a culture of P. polymyxa. Adsorption of cells and metabolic products onto minerals and electrokinetic studies of minerals after interaction with cells and metabolic products were carried out to examine the resulting surface modification on the mineral surfaces. Flocculation and flotation techniques were successfully applied in the selective separation of minerals after bacterial interaction. The effect of varying conditions for production of extracellular polysaccharides and protein provided an insight into the possible mechanism involved in microbially induced flocculation and flotation of pyrite and galena.
Keywords: Extracellular biopolymers; Adsorption; Flocculation; Flotation; Pyrite; Galena;

The recently published points of zero charge (PZC) of various materials are compiled to update previous compilations [M. Kosmulski, Chemical Properties of Material Surfaces, Dekker, New York, 2001; M. Kosmulski, J. Colloid Interface Sci. 253 (2002) 77; M. Kosmulski, J. Colloid Interface Sci. 275 (2004) 214]. The recent results corroborate the previously found PZC with a few exceptions. The PZC of alumina obtained from the second-harmonic generation response is substantially lower than the PZC obtained by means of standard methods, while for titania the difference is less significant. PZC of Tl2O3 at pH 7.9 was reported for the first time. A surprisingly insignificant temperature effect on the IEP of rutile was found. Recent model studies aimed at explanation of the effect of the nature of 1–1 electrolytes on the course of charging curves and of discrepancies in the PZC of different materials having the same chemical formula are summarized.The PZC/IEP of alumina reported in recent papers.
Keywords: Point of zero charge; Isoelectric point; Surface charge; Zeta potential;

Stabilizer-free nanosized gold sols by Daniel Andreescu; Tapan Kumar Sau; Dan V. Goia (742-751).
The paper describes a convenient, rapid, and reproducible method for the synthesis of stable dispersions of uniform gold nanoparticles at ambient temperatures by mixing aqueous solutions of tetrachloroauric acid and iso-ascorbic acid. The influence of the experimental conditions on the size of the gold particles and the stability of the final sols was monitored by dynamic light scattering and UV–vis spectrophotometry. It was found that the size of the resulting nanoparticles is affected by the concentration and the pH of gold solution, while the stability of the electrostatically stabilized final sols is strongly dependent on the excess of reductant in the system, the ionic strength, and the temperature of the precipitation. Since the preparation process does not require the addition of a dispersing agent, the surface of the resulting gold nanoparticles can be easily functionalized to make them suitable for applications in medicine, biology, and catalysis.The paper describes a convenient and reproducible method to synthesize stable gold sols in the absence of dispersants by rapidly mixing HAuCl4 and iso-ascorbic acid aqueous solutions at ambient temperature.
Keywords: Gold nanoparticles; Gold sol; Iso-ascorbic acid; Plasmon band; Stabilizer; Tetrachloroauric acid;

A novel simplified method for synthesis of surface-enhanced Raman scattering tags has been reported. This synthesis method is based on reverse micelle technique using Igepal CO-520 as a surfactant and the mixed solution of silver nitrate and rhodamine dyes with isothiocyanate group as water pool followed by hydrazine hydrate reduction and TEOS polymerization leading to the formation of silica layer surrounding the silver core. Compared to the method reported in literature, the proposed methodology eliminates the necessity of vitrophilic pretreatment and makes it possible to complete all different processes including the preparation of silver nanoparticles, the conjugation of dye molecules and the formation of silica shell in the microreactor. The nanoparticle-based surface-enhanced Raman tags obtained are composed of silver core conjugated with rhodamine dyes and an encasing silica shell. Both the dyes themselves and the Ag/SiO2 core–shell nanoparticles without the encapsulation of dyes exhibit no Raman signals. However, the Ag/SiO2 core–shell nanoparticles exhibit strong Raman signals when encapsulated with these dyes. This is due to the appearance of fluorescence quenching and surface-enhanced Raman scattering effect resulting from the conjugation of dyes and silver core. The Raman tags were characterized using transmission electron microscopy (TEM), UV–visible absorption spectrometry, and Raman spectrometry.Ag/SiO2 core–shell nanoparticle-based surface-enhanced Raman tags have been developed using reverse microemulsion technology which possesses the property that all the reactions involved are completed in a microreactor.
Keywords: Surface-enhanced Raman scattering; Core–shell nanoparticles; Microemulsion;

Study on the formation and depolymerization of acridine orange dimer in acridine orange–sodium dodecyl benzene sulfonate–protein system by Fei Wang; Jinghe Yang; Xia Wu; Xiaobo Wang; Lishun Feng; Zhen Jia; Changying Guo (757-764).
Experiment indicates that the fluorescence of acridine orange (AO) can be greatly quenched by anionic surfactant sodium dodecyl benzene sulfonate (SDBS), but when protein is added into the AO–SDBS system, the fluorescence intensity of the latter is enhanced. It is considered that SDBS can promote the formation of AO dimer, resulting in the quenching of the fluorescence of AO. When bovine serum albumin (BSA) is added into AO–SDBS system, BSA and SDBS can interact and form negative micelle-like cluster complex with “aromatic ring stacking,” which destroys the formation conditions of AO dimer and makes some AO dimers turn into monomer, resulting in the fluorescence enhancement of AO–SDBS system. Whereas the positive AO and residual AO dimer are dissolved in the negative BSA–SDBS cluster through electrostatic and hydrophobic forces and form a large association. Here, the fluorescence enhancement of AO–SDBS is considered to originate from the hydrophobic microenvironment provided by BSA and SDBS, the depolymerization of AO dimer and intermolecular energy transfer between BSA and AO.The interaction model of the BSA–AO–SDBS system.
Keywords: Formation; Depolymerization; Acridine orange dimer; Protein; Surfactant;

Surface enhanced Raman scattering based on silver dendrites substrate by Wei Song; Yuchuan Cheng; Huiying Jia; Weiqing Xu; Bing Zhao (765-768).
A simple method of the reduction of AgNO3 by copper foil in aqueous medium was used to prepare silver dendrites, which can be used as a novel good reproducible surface enhanced Raman scattering (SERS) active substrate. The SERS spectra of 4-pyridinethiol on this novel substrate reflected the different SERS activities on the minuteness and strong Ag dendrites. The electromagnetic coupling enhancement and chemical enhancement mechanisms are used to explain the SERS effect.A novel surface enhanced Raman scattering (SERS) active substrate of silver dendrites was prepared by reduction of AgNO3 by copper foil in aqueous medium.
Keywords: Surface enhanced Raman scattering; Ag dendrites; Copper foil;

The surface fluorescence of methyl orange (MO) adsorbed onto colloidal silver was investigated. It was found that the 420 nm fluorescence band of MO aqueous solution quenched sharply. While the enhancement factor of the other fluorescence band at 530 nm was up to 20, and at the same time, the band had a red shift of 30 nm. These notable phenomena are explained in the main aspects of the influence of fluorescence quenching and fluorescence enhancing by the radiationless energy transfer channel.
Keywords: Methyl orange; Silver particles; Fluorescence quenching and enhancing; Radiationless energy transfer;

Effect of temperature on the acid–base properties of the alumina surface: Microcalorimetry and acid–base titration experiments by Jean-Pierre Morel; Nicolas Marmier; Charlotte Hurel; Nicole Morel-Desrosiers (773-779).
Sorption reactions on natural or synthetic materials that can attenuate the migration of pollutants in the geosphere could be affected by temperature variations. Nevertheless, most of the theoretical models describing sorption reactions are at 25 °C. To check these models at different temperatures, experimental data such as the enthalpies of sorption are thus required. Highly sensitive microcalorimeters can now be used to determine the heat effects accompanying the sorption of radionuclides on oxide–water interfaces, but enthalpies of sorption cannot be extracted from microcalorimetric data without a clear knowledge of the thermodynamics of protonation and deprotonation of the oxide surface. However, the values reported in the literature show large discrepancies and one must conclude that, amazingly, this fundamental problem of proton binding is not yet resolved. We have thus undertaken to measure by titration microcalorimetry the heat effects accompanying proton exchange at the alumina–water interface at 25 °C. Based on (i) the surface sites speciation provided by a surface complexation model (built from acid–base titrations at 25 °C) and (ii) results of the microcalorimetric experiments, calculations have been made to extract the enthalpic variations associated respectively to first and second deprotonation of the alumina surface. Values obtained are Δ H 1 = 80 ± 10   kJ mol −1 and Δ H 2 = 5 ± 3   kJ mol −1 . In a second step, these enthalpy values were used to calculate the alumina surface acidity constants at 50 °C via the van't Hoff equation. Then a theoretical titration curve at 50 °C was calculated and compared to the experimental alumina surface titration curve. Good agreement between the predicted acid–base titration curve and the experimental one was observed.Acid–base titration of 1 g/L of alumina at 50 °C: experimental results and modeling.
Keywords: Alumina; Microcalorimetry; Sorption; Temperature effect;

Effect of surface hydrophobicity/hydrophilicity of mesoporous supports on the activity of immobilized lipase by Jing He; Yan Xu; Hui Ma; Qiong Zhang; David G. Evans; Xue Duan (780-786).
Taking advantage of the virtue of hydrophilic surface, lipase was firstly immobilized on SBA-15 as a support. Then the surface of the SBA-15 with enzyme entrapped inside the channels was modified by grafting with organic moieties. It has been found that the silylation with n-decyltrimethoxysilane (DE) and 3-(trimethoxysilyl)propyl methacrylate (MA) following the lipase immobilization increases the surface hydrophobicity. But the surface modified by MA shows more hydrophilicity than that modified by DE. The activity assay indicates that the hydrolytic activity for the hydrolysis of insoluble or partly soluble substrates increases with enhanced surface hydrophobicity.The surface property of the support entrapping PPL plays a significant role in the catalytic activity of lipase immobilized. The hydrolytic activity for the hydrolysis of insoluble or partly soluble substrates increases with enhanced surface hydrophobicity.
Keywords: Hydrophobicity/hydrophilicity; Mesoporous support; Lipase immobilization; Grafting;

Zinc oxide was prepared by different methods by varying precipitating agents, the source of the salt precursors and the microwave irradiation time and was characterized by XRD, BET-surface area, surface acidity and crystallite sizes. The photocatalytic reactions were carried out under solar radiation in batch reactors towards oxidation of 4-nitrophenol and reduction of Cr(VI) by varying different parameters such as irradiation time, pH of the solution, catalyst amount and substrate concentration and the activities were correlated with the physico-chemical parameters. Zinc oxide samples prepared by microwave irradiation and calcined at 300 °C exhibit highest surface area, acid sites and lowest crystallite sizes and show highest activity towards photocatalytic reactions.Microwave irradiation has beneficial effect on photocatalytic activity of ZnO. Microwave irradiated sample heated at 300 °C shows more surface area, less crystallinity size and hence it shows better activity among all the samples. Under optimization of reaction conditions, 15 min microwave irradiated sample in 0.6 g/L dose shows 92 and 98% photodegradation of 4-nitrophenol and photoreduction of Cr(VI), respectively.
Keywords: Photocatalytic degradation; Microwave irradiation; Hydrozincite; Photocatalytic activity;

Characterization of the reactivity of a silica derived from acid activation of sepiolite with silane by 29Si and 13C solid-state NMR by J.L. Valentín; M.A. López-Manchado; P. Posadas; A. Rodríguez; A. Marcos-Fernández; L. Ibarra (794-804).
The mechanism of the reaction between a silica sample coming from acid treatment of sepiolite (denominated Silsep) and an organosilane, namely bis(triethoxysilylpropyl)tetrasulfane (TESPT), has been evaluated by solid state NMR spectroscopy, being compared with the silanization reaction of a commercial silica. The effect of the silane concentration and temperature on the course of the reaction was considered. Experimental results indicate that the silanization reaction is more effective in the case of Silsep, favoring both the reaction of silane molecules with the filler surface and the reaction between neighboring silane molecules. This different behavior is attributed to structural factors, moisture, and number of acid centers on silica surface. Environmental scanning electron microscopy (ESEM) was used to deposit micrometric water drops on the surface of these samples and to evaluate the proportion and distribution of the organophylization process.
Keywords: Surface modification; Silanization; Organosilane; Bis(triethoxysilylpropyl)tetrasulfane (TESPT); Silica; Sepiolite; Acid treatment; Solid state NMR spectroscopy; Environmental scanning electron microscopy (ESEM); Rubber;

Yellowish S-containing TiO2 (S–TiO2) powders were prepared by calcination of a mixture of titanium(III) chloride and ammonium thiocyanate solutions. Three kinds of S–TiO2 were prepared by varying the concentration of ammonium thiocyanate (0.5, 1 or 13 M). X-ray photoelectron spectroscopy spectra of the S–TiO2 showed that sulfur atoms existed on the surface of TiO2 powders. But the peaks assigned to S disappeared after Ar+ etching, which means that these atoms were not doped in the bulk of the TiO2 powders. While UV–visible absorption spectra of S–TiO2 showed that the absorption edges of these photocatalysts were seen to shift to a longer wavelength (lower band gap energy) than those of undoped rutile TiO2 prepared and commercial anatase type TiO2 (ST-01). The S–TiO2 (1 M) exhibited higher photocatalytic activity than ST-01 for degradation of methylene blue in aqueous solution under visible light irradiation ( λ > 400   nm ). It was also confirmed by IR spectroscopy that acetaldehyde in oxygen under visible light irradiation ( λ > 400   nm ) was decomposed to acetic acid by the S–TiO2 and ST-01 at the first decomposition step.The S-containing TiO2 (1 M) exhibited higher photocatalytic activity than the commercial anatase type TiO2 (ST-01) for degradation of methylene blue in an aqueous solution under visible light irradiation ( λ > 400   nm ).
Keywords: Spectroscopic study; Photocatalytic decomposition; Titanium dioxide containing sulfur;

The local thinning of a viscous liquid film on a substrate driven by a surface (or interfacial) tension gradient due to a concentration gradient of a monolayer of an insoluble surfactant initially non-uniformly distributed at a liquid interface relevant to chemical engineering, biomedical and other applications is investigated. A simple model is presented for the temporal evolution of the profiles of radial variation in the thickness of a thin liquid film, the effects of gravity and capillarity due to deformation of the interface in slowing down the film thinning process being allowed. As time increases, the surfactant spreads and the radius of its front increases inversely with decrease in the two-third power of the film thickness at the center. The model describes well not only the published experimental results but also those obtained by other authors using numerical simulations of a set of coupled partial differential equations.Local film thinning at the center during the approach of a bakelite sphere to the interface between liquid paraffin and glycerol containing 0.1% (by volume) of Tween 80. Broken line: Published numerical solution. Full line: Present analytical model (no gravity). Dotted line: Present model with gravity.
Keywords: Coalescence; Film thinning; Interfaces; Marangoni flow; Surface or interfacial tension gradient; Surfactant spreading;

Surface characterizations of mono-, di-, and tri-aminosilane treated glass substrates by E. Metwalli; D. Haines; O. Becker; S. Conzone; C.G. Pantano (825-831).
The surface properties and structure of mono-, di-, and tri-aminosilane treated glass surfaces were investigated using surface analytical techniques including X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, atomic force microscopy (AFM), and streaming potential. An optimized dip-coating process was demonstrated to produce roughly silane monolayer coverage on the glass surface. The surface charge measurements indicated that aminosilanization converts the glass surface from negative to positive potentials at neutral pH values. Higher positive streaming potential was observed for tri-compared with mono- and di-aminosilane treated glass surfaces. For all aminosilane treated glass samples, the high-resolution N 1s XPS spectra indicated a preferential orientation of the protonated amino-groups towards the glass surface whereas the free amino groups were protruding outward. This study aimed to obtain uniform, reproducibly thin, strongly adhering, internally cross-linked, and high positively charged aminosilane-coated glass surfaces for the attachment of DNA fragments used in microarraying experiments.Molecular orientations study indicates a preference for protonated amino groups towards the glass surface while the free amino groups are protruding to the air-side.
Keywords: Glass surface; Aminosilane; Microarrays; XPS; Molecular orientation; Raman;

Using a new computational model, we have studied the dynamics and coalescence of a pair of two-dimensional droplets in pressure-driven flow through a constricted capillary tube, which is a prototype problem for the analysis of the interaction of emulsion droplets in porous media. We present simulations that quantify the effects of various system parameters on the droplet stability. These include the capillary number, the interfacial tension, the suspended-to-suspending-phase viscosity ratio, the valence and concentration of added electrolytes, the droplet-to-pore-size ratio, the pore-body-to-throat-size ratio, and the type of pore geometry. Our simulations show that the capillary number Ca plays an important role in determining whether the drops coalesce. At low Ca, drops deform only slightly and coalescence occurs at the entrance of the pore throat, whereas significant deformation enables the drops move through the pore without coalescence at high Ca. Coalescence is favored at intermediate values of the viscosity ratio. The destabilizing effect of added electrolytes is found to be insignificant for 10-μm drops, but significant for micron-size drops. Among the geometric-related parameters, the drop-to-pore-size ratio is the most significant.The image shows a simulation of droplets flowing through a constriction at Ca = 0.1 . At Ca ∼ 0.05 and below, drop deformation is not as pronounced, which in turn leads to coalescence.
Keywords: Emulsion stability; Droplet coalescence; BEM; Porous media;

Highly charged cation permeable composite membranes were prepared by blending of sulfonated poly(ether sulfone) (SPES) with sulfonated poly(ether ether ketone) (SPEEK) in 0 to 90% weight ratio, to adjust the hydrophobic properties and ion selective nature. Extent of sulfonation was confirmed by 1H NMR and ion exchange capacity and degree of sulfonation depending on blending composition. These membranes were characterized as a function of weight fraction of SPEEK by recording ion-exchange capacity, water uptake, thermogravimetric analysis, membrane conductivity and membrane potential in equilibration with different electrolytic solutions. Membrane permselectivity and solute flux were estimated using these data on the basis of non-equilibrium thermodynamic principles and for observing the selectivity of different membranes for mono- or bivalent counter-ions. It was observed that relative selectivity for monovalent in comparison to bivalent counter-ions were increased with the decrease in SPEEK content in the composite membrane matrix. The range of SPEEK content in the blend from 60 to 80% appears the most suitable for the selective separation of monovalent ions from bivalent ions. Furthermore, highly charged nature and stabilities of these membranes extend their applications for the electro-assisted separations of similarly charged ions as well as other electro-membrane processes.Relative permeability of mono-valent ions (η i) with respect to bivalent ions across the composite membranes with 50–60% (w/w) SPEEK content suggests selectively separation of monovalent ions from bivalent ions by electro-assisted membrane separation techniques.
Keywords: Ion-exchange membrane; Sulfonated poly(ether ether ketone); Sulfonated poly(ether sulfone); Membrane permselectivity; Polymer blend; Electrodialysis;

Functionalization of montmorillonite clay has been done using 3-aminopropyltriethoxysilane in the presence of various solvent media. Qualitative evidence of the presence of aminosilane attached to the clay platelets have been identified using Fourier transform infrared spectroscopy (FTIR) and 29Si and 13C solid-state nuclear magnetic resonance (NMR) spectroscopy. Grafting yield has been calculated using thermogravimetric analysis and total grafting yield increases with the solvent surface energy. X-ray diffraction studies of the silane functionalized montmorillonite clay exhibits two peaks, which may be attributed to intercalation and surface interaction with the broken edge platelets. Functionalized clay has been characterized by surface area measurements to understand the influence of solvents on the surface area of the functionalized clay.
Keywords: Montmorillonite; 3-Aminopropyltriethoxysilane; Solvent surface energy; Adsorption; Intercalation; Surface functionalization;

This study examined shape changes in two typical wastewater flocs subjected to cyclic freezing and thawing and the associated force exerted by the ice front. While freezing, the engulfing ice front gradually pulled the floc apart. Subsequent thawing only partially restored the floc's shape. By the Maxwell model, used to interpret gross shape deformations, both flocs were visco-elastic objects exhibiting time-varying rheological characteristics which were more viscous than elastic. Detailed observations of floc 1 deformation demonstrated a two-stage force–displacement relationship. Following 1 cycle of freezing and thawing, the interior structure of the floc deteriorated and the force required to elongating a unit length of floc decreased by 60%. The original floc 2 had a dense “core” and loose “tail”; the core was more resistant to deformation under normal stress than the loose tail. Although both flocs had similar shapes and sizes and were acquired from the same activated sludge stream at a wastewater treatment plant, their rheological behaviors differed substantially. A comprehensive theoretical model for freezing and thawing processes should incorporate these rheological characteristics as they corresponded to observed structural changes and reduction in bound water content in sludge following a cyclic treatment of freezing and thawing.Fig. 2 shows the morphology change after cyclic freezing test for floc and for solid sphere at freezing speed of 5.0 μm/s.
Keywords: Freezing; Thawing; Floc; Shape deformation; Force;

Deformation of water droplets on solid surface in electric field by A. Moukengué Imano; A. Beroual (869-879).
The purpose of this paper is to analyze the deformation of water droplets on a solid surface under electric stress. A mathematical model making it possible to simulate the axisymmetric as well as non-axisymmetric deformations of droplets is developed. According to this model, the droplet deformation depends on several parameters such as the volume and the number of droplets, the conductivity and the permittivity of droplets, their proximity to one another, the surface of the solid material, and the location of each droplet on the dielectric surface. The results of the simulation show the disturbance of the background field through the presence of a single or multiple droplets. An experimental study is also achieved by considering one to three droplets aligned simultaneously on a dielectric smooth surface between two electrodes subjected to AC voltages. The influence of the background field and the droplet location regarding the electrodes on the deformation of water droplets are evidenced.The figure shows a computed 3D shape of deformed water droplet placed in the center between two electrodes. The droplet elongates symmetrically toward the electrodes in X-direction.
Keywords: Dielectric solid surface; Sessile droplet; Contact angle; Interfacial tension; Electric field strength; Weber number;

A generalized analysis of capillary flows in channels by Yan Xiao; Fuzheng Yang; Ranga Pitchumani (880-888).
Investigations on the motion of a fluid in capillary geometries have been extensively reported in the literature using both experimental and theoretical approaches. In this paper, the theories for capillary flow are generalized to a unified nonlinear second-order differential equation which takes the effects of the entrance, the inertial forces, and the dynamic contact angle into account. An analytical solution of the differential equation is obtained in the form of a double Dirichlet series. The readily evaluated analytical solution is compared with experimental and numerical results in the literature, which shows a good agreement. It is demonstrated that this analytical approach can be used to predict capillary flows for a wide range of fluids and parallel-plate and tube geometries in a unified manner.Capillary rise in microchannel and tube configurations.
Keywords: Capillary flow; Dynamic contact angle; Analytical model; Minichannels; Tube; Parallel plates;

The interfacial property in polymer–liquid crystal systems is quite different from flexible polymer–polymer mixtures due to the anisotropic properties of liquid crystals. The apparent interfacial tension between a liquid crystal and a flexible polymer was measured by deformed droplet retraction method. The deformation and recovery of a single liquid crystal droplet dispersed in a poly(dimethylsiloxane) matrix were realized by a transient shear flow and observed by polarized optical microscope. The apparent interfacial tension of polymer–liquid crystal system was found to be greatly dependent on the temperature, initial droplet deformation and liquid crystal droplet size.The interfacial property in polymer–liquid crystal systems is quite different from flexible polymer–polymer mixtures due to the anisotropic properties of liquid crystals. The apparent interfacial tension between a liquid crystal and a flexible polymer was measured by deformed droplet retraction method. The deformation and recovery of a single liquid crystal droplet dispersed in a poly(dimethylsiloxane) matrix were realized by a transient shear flow and observed by polarized optical microscope. The apparent interfacial tension of polymer–liquid crystal system was found to be greatly dependent on the temperature, initial droplet deformation and liquid crystal droplet size.
Keywords: Liquid crystal; Anisotropy; Interfacial tension;

The stability of wetting states, namely the Cassie state (partial wetting) and the Wenzel state (complete wetting) of surfaces with protrusions, is determined by comparing the total free energy of a liquid drop in terms of their apparent contact angles for different protrusion features. It is found that when the area fraction of the topographical features and the intrinsic contact angle for a flat surface are large, the Cassie state is favored, but it can be either the metastable or stable state. It is shown that the transition from the Cassie state to the Wenzel state requires the application of a pressure to the meniscus between the surface protrusions. The critical transition pressure increases not only with increasing area fraction and intrinsic contact angle, but also with decreasing protrusion size. During the transition, a high-pressure gas can be trapped around the protrusions that can cause the Cassie state to be recovered after the release of the applied pressure. The analysis shows that a droplet can ‘hang’ upside-down when the protrusion size is very small; namely, the protrusions can pin the meniscus. These results are discussed relative to the advancing and receding contact angle.
Keywords: Superhydrophobic; Wetting state; Wetting stability; Protrusion size; Cassie equation; Wenzel equation; Transition pressure;

To demonstrate an important distinction between the electrolytes and nonelectrolytes, surface tension of aqueous solutions of typical nonelectrolytes, sucrose and glucose, was measured as a function of temperature and concentration. The presence of sucrose or glucose molecules in the surface region affects the surface tension in the same way as the presence of an ion does. There is, however, a difference in the temperature coefficient of the surface tension between typical nonelectrolyte solutions, sucrose and glucose, and alkali halide solutions. The entropy of surface formation of sucrose and glucose solutions is the same as that of pure water, while that of alkali halide solutions decreases with concentration. The relation between this entropy change and the formation of electric double layers was discussed.
Keywords: Surface tension; Thermodynamic quantities; Electrolytes; Glucose; Sucrose;

Concentration of hydrogen nanobubbles in electrolyzed water by Kenji Kikuchi; Yoshinori Tanaka; Yasuhiro Saihara; Miho Maeda; Masaaki Kawamura; Zempachi Ogumi (914-919).
The hydrogen concentration of solutions supersaturated with hydrogen comprising dissolved hydrogen and hydrogen bubbles obtained through water electrolysis was studied. The rate of decrease in concentration of hydrogen nanobubble diameter below 600 nm and dissolved hydrogen with elapsed time after electrolysis was seemed to be independent of ionic strength and ion type and storage temperature. The concentration of hydrogen nanobubbles (mol dm−3) in electrolyzed water decreases with ionic strength, while the total hydrogen concentration remains roughly constant. The hydrogen nanobubble concentration increases in accordance with the nature of ions existing in solution in the following order I < Br < Cl and K+ < Li+ < Na+. It is shown that the ratio of hydrogen nanobubble concentration to total hydrogen concentration of hydrogen in a catholyte strongly depends on the ratio in the supersaturated hydrogen solution near the electrode surface.
Keywords: Coalescence of bubbles; Hydrogen nanobubbles; Hydrogen evolution; Supersaturation; Water electrolysis;

Surfactant-mediated water transport at gelatin gel/oil interfaces by V.I. Uricanu; M.H.G. Duits; D. Filip; R.M.F. Nelissen; W.G.M. Agterof (920-934).
We studied spontaneous emulsification (SE) at Water/Oil (W/O) interfaces, using several types of aqueous reservoirs immersed in dodecane plus Span80 surfactant. Above a threshold surfactant concentration C SE , aqueous satellite droplets are formed at the W/O interface. Varying the aqueous reservoir size, from below 100 μm (droplets) to centimeters (macroscopic phases), allowed investigating SE with complementary techniques. Release (rates) and size distributions for SE droplets were measured with microscopy. For gelled aqueous phases, water expulsion due to SE was quantified. Values for C SE were measured and were found to be higher for aqueous phases containing gelatin and/or NaCl. We also studied water exudation during network building and syneresis in aqueous gelatin gels immersed in dodecane/Span80. Below C SE (i.e., in the absence of SE) this process is still responsible for significant physico-chemical changes at the W/O interface. To study these in more detail, we performed atomic force microscopy experiments (in force–distance mode) on macroscopic gels. Both changes in the local elastic response and in the wettability of the AFM tip were detected. Together they suggest the formation of “water pockets” after prolonged (gel) setting times, along with a densification of the interfacial gelatin network.Above a threshold concentration, C SE , of Span 80 in dodecane, satellite droplets are expelled from an aqueous reservoir. Values for C SE were found to be higher for aqueous phases containing gelatin and/or NaCl. Below C SE , gelatin gel syneresis is responsible for significant physico-chemical changes at the gel/oil interface.
Keywords: Spontaneous emulsification; Gelatin gel; Water exudation; Atomic force microscopy; Elasticity; Surfactant;

Interface of AOT/Brij mixed reverse micellar systems: Conductometric and spectrophotometric investigations by Sujan Chatterjee; Rajib Kumar Mitra; Bidyut Kumar Paul; Subhash Chandra Bhattacharya (935-941).
Solubilization and conductivity studies are carried out with AOT/Brijs (Brij-30, Brij-35, Brij-52, Brij-56, Brij-58, Brij-72, Brij-76, Brij-78)/isooctane/water mixed reverse micellar systems. Replacement of AOT molecules with large head group Brij molecules (Brij-30, Brij-35, Brij-56, Brij-58, Brij-76, Brij-78) decreases the solubilization capacity, whereas those with smaller polar head groups (Brij-52 and Brij-72) increases it. The former blends assist the conductance percolation whereas the latter retard it. An attempt has been taken to obtain more insight on the interfacial composition of the mixed interface with the help of spectrophotometric studies using 7-hydroxycoumarin as the fluorophore. The results obtained from the solubilization and conductometric studies have been correlated with those obtained from the spectroscopic studies.Interface of the AOT/Brij/isooctane/water reverse micellar systems has been investigated conductometrically and spectrophotometrically using 7-hydroxycoumarine as the fluorophore.
Keywords: Solubilization; Conductivity; Mixed reverse micelles; 7-hydroxycoumarin (HCM); Photophysical studies;

Role of the counterion in the effects of added ethylene glycol to aqueous alkyltrimethylammonium micellar solutions by Amalia Rodríguez; María Muñoz; María del Mar Graciani; María Luisa Moyá (942-951).
The influence of the addition of various amounts of ethylene glycol, EG, up to a weight percent of 50%, on the micellization process in N-hexadecyl, N-tetradecyl, and N-dodecyltrimethylammonium chloride micellar solutions was investigated. Conductivity, fluorescence, and spectroscopic measurements give information about changes in the cmc, in the micellar ionization degree, in the aggregation number and in the polarity of the interfacial region upon changing the percentage by weight of the organic solvent. These changes were compared to those found when ethylene glycol was added to the analogous alkyltrimethylammonium bromide aqueous micellar solutions, results showing that the effects caused by the presence of the organic solvent were practically independent of the counterion nature. This conclusion was in agreement with the micellar kinetic effects observed on the spontaneous hydrolysis of phenyl chloroformate in both water–ethylene glycol alkyltrimethylammonium bromide and chloride micellar solutions.
Keywords: Micelles; Cationic; Ethylene glycol; Water; Alkyltrimethylammonium surfactants; Micellization; Solvophobic effect;

The solubility of ethylene in aqueous solutions of sodium dodecyl sulfate (SDS) at different concentrations was measured at temperature 298.2 K and near the hydrate formation region. The effect of SDS on the gas solubility was studied and the solubilities of ethylene in a single micelle under different conditions were evaluated. It was found that the micelle solubilization was obvious, especially in the region near hydrate formation conditions. The CMC of SDS solution was also evaluated based on the solubility vs SDS concentration curves and it was found that it decreased with decreasing temperature.The solubilities of ethylene in SDS aqueous solution vary with SDS concentration and system conditions. The micelle solubilization near hydrate formation region is much stronger than that at ambient temperature.
Keywords: Solubility; Water; Ethylene; Sodium dodecyl sulfate; Hydrate;

We have investigated the influence of the magnetic field strength, shear rate, and rotational Brownian motion on transport coefficients such as viscosity and diffusion coefficient, and also on the orientational distributions of rodlike particles of a dilute colloidal dispersion. The rodlike particle is modeled as a magnetic spheroidal particle which has a magnetic moment normal to the particle axis; such a particle may typically be a hematite particle. In the present study, an external magnetic field is applied in the direction normal to the shear plane of a simple shear flow. The basic equation of the orientational distribution function has been derived from the balance of torques and solved numerically. The results obtained here are summarized as follows. Although the orientational distribution function shows a sharp peak in the shear flow direction for a very strong magnetic field, such a peak is not restricted to the field direction alone, but continues in every direction of the shear plane. This is due to the characteristic particle motion that the particle can rotate around the axis of the magnetic moment in the shear plane, although the magnetic moment nearly points to the magnetic field direction. This particle motion in the shear plane causes negative values of the viscosity due to the magnetic field. The viscosity decreases, attains a minimum value, and then converges to zero as the field strength increases. Additionally, the diffusion coefficient is significantly influenced by such characteristic particle motion in the shear plane for a strong magnetic field.The characteristic motion of the magnetic rodlike particle in a simple shear flow under circumstances of an external magnetic field causes negative values of the viscosity due to the magnetic field. η y x M = viscosity due to magnetic properties; ξ=non-dimensional magnetic field strength; Pe=Péclet number.
Keywords: Ferromagnetic colloidal dispersion; Aggregation phenomena; Simple shear flow; Spheroidal particle; Orientational distribution function; Rheological properties; Viscosity; Diffusion coefficient;

Intrinsic viscosity of SiO2, Al2O3 and TiO2 aqueous suspensions by F.J. Rubio-Hernández; M.F. Ayúcar-Rubio; J.F. Velázquez-Navarro; F.J. Galindo-Rosales (967-972).
The viscosity of dilute suspensions of several metal oxides (SiO2, Al2O3 and TiO2) was measured at different pH values. The intrinsic viscosity, [ η ] , was derived from the concentration dependence of the viscosity. This magnitude was pH-dependent. A correlation with the shape of the kinetic unity has been proposed.The viscosity of dilute suspensions of several metal oxides (SiO2, Al2O3 and TiO2) was measured at different pH values. The intrinsic viscosity, [ η ] , was derived from the concentration dependence of the viscosity. This magnitude was pH-dependent. A correlation with the shape of the kinetic unity has been proposed.
Keywords: Intrinsic viscosity; Suspensions; Oxides; Colloids; Electroviscous effects;

Dielectric properties of four suspensions of spherical polystyrene particles were measured at 25 °C over a broad frequency range extending from 100 Hz to 10 MHz, using a HP 4192 A Impedance Analyzer. The instrument was coupled to a cell with parallel platinum black electrodes and variable spacing, and the quadrupole calibration method was used. The aqueous electrolyte solutions were prepared using equal concentrations of NaCl, KCl, NaAc, or KAc, so that the calculated Debye screening length and Zeta potential remained constant, while the conductivity changed. The polystyrene particles used (Interfacial Dynamics Corp., surfactant-free white sulfate latex) have a diameter of 1 micron and a surface charge density that is independent of the pH. The dielectric spectra were described using the Nettelblad–Niklasson expression combined with a Debye type high-frequency term and analyzed using the Shilov–Dukhin theory and numerical results. The theoretical prediction that the low-frequency dispersion parameters are determined by the co-ion diffusion coefficient was experimentally confirmed. This also allowed to justify an alternative definition of the characteristic time of the low-frequency dispersion. On the contrary, the prediction that the high-frequency dispersion parameters are determined by the diffusion coefficient of counterions could not be confirmed, possibly due to experimental problems. However, the ζ-potential values deduced from high-frequency data were compatible with values deduced from electrophoretic mobility measurements.Theory predicts that the low-frequency dielectric spectra of colloidal suspensions are determined by the mobility of co-ions while the high-frequency by that of counterions. This prediction is partly confirmed by experimental results.
Keywords: Dielectric dispersion; Diffusion coefficients; Colloidal suspensions; Polystyrene particles; Counterions; Co-ions; Dielectric spectroscopy; Permittivity; Conductivity;

Interaction forces between poly(amidoamine) (PAMAM) dendrimers adsorbed on gold surfaces by Daisuke Hiraiwa; Tomokazu Yoshimura; Kunio Esumi (982-986).
Interaction forces between two gold surfaces with adsorbed poly(amidoamine) (PAMAM) dendrimers (generations G3.0 and G5.0) have been investigated using colloidal probe atomic force microscopy (AFM). In the absence of dendrimers or at their low concentrations, an attractive force derived from the van der Waals interaction was observed. On the other hand, this attractive interaction changed to repulsion with increasing dendrimer concentration. The origin of the repulsion can be attributed to either an electric double layer interaction or a steric effect of the adsorbed dendrimers, depending on the concentration of dendrimer. The steric hindrance was also influenced by the generation of the dendrimer; the force-detectable distance in the presence of PAMAM G5.0 dendrimer was slightly longer than that in the presence of G3.0 dendrimer. In order to estimate the occupied area of each dendrimer adsorbed on gold, quartz crystal microbalance (QCM) measurement was also carried out.Interaction forces between PAMAM dendrimer adsorbed on gold surfaces were studied from the viewpoints of dendrimer concentration, the pH of solution, and generation number.
Keywords: Colloidal probe atomic force microscope; Poly(amidoamine) dendrimer; Gold surface; Quartz crystal microbalance;

Silicones are special reagents that impart desired surface properties such as softness, bounciness and antiwrinkle properties to fabrics and related materials. Although these finishing processes have been practiced routinely, very little is known about the mechanisms involved in modification so that they could be improved. The current study was undertaken to develop basic understanding of the mechanisms responsible for surface modification of fibers using silicones. PDMS based amino silicone emulsions, quaternized to various degrees using dimethyl sulphate, were used in the present study. The electrokinetic properties of the modified silicones were studied as a function of pH. It was expected that the silicone emulsions would show a steady positive zeta potential throughout the pH range due to the quaternization by dimethyl sulphate. Surprisingly, a sudden drop in the zeta potential was observed around pH 8 with the samples turning hazy in the pH range of 8–10. Turbidimetric studies also showed a sudden increase in the turbidity in the pH range 8–10 where commercial processes also encounter problems. It was concluded that the emulsions were destabilized at pH 8–10 thus rendering them ineffective for surface treatment. In order to identify reason for the improvement in fabric properties, fiber structure was monitored using atomic force microscopy. It was observed that the treated fibers were far smoother, relaxed and uniform as compared to the untreated fibers. Thus the morphology of the fabric is modified in a specific way by treatment with specialty silicones.Fiber structure studied using atomic force microscopy shows that the silicone treated fibers (right) were far smoother, relaxed and uniform as compared to the untreated fibers (left).
Keywords: Silicone emulsions; Fabric finishing; Zeta potential; AFM;

Thermo-induced formation of physical “cross-linking points” of PNIPAM-g-PEO in semidilute aqueous solutions by Hongwei Chen; Weiwei Li; Hui Zhao; Jiangang Gao; Qijin Zhang (991-995).
Linear poly(N-isopropylacrylamide) chains grafted with short poly(ethylene oxide) chains (PNIPAM-g-PEO) were prepared by free radical copolymerization of NIPAM and PEO macromonomers ( M w = 5000   g / mol ) end-capped with methacrylate in water. Temperature effects on the solution viscosity of thermally sensitive copolymer were studied in different aqueous concentrations. A specific transition was observed during the measurement of the reduced viscosities of PNIPAM-g-PEO copolymer at a certain concentration ( C 0 ) in semidilute aqueous solutions: the reduced viscosities increased sharply (namely, thermothickening behavior) at LCST when concentrations were higher than C 0 , or decreased sharply at LCST when concentrations lower than C 0 . A plateau was also found near C 0 when temperature was closing to LCST from low temperature, showing there is no change in reduced viscosity under this circumstance. The inverse increase of the viscosities at higher temperatures in higher concentration ( > ∼ 3   g / L ) is attributed to the forming of physical “cross-linking points” composed of collapsed PNIPAM core and expanded PEO shell. The sharp decrease of the viscosities at higher temperatures in lower concentration ( < ∼ 3   g / L ) is attributed to the forming of independent globules. The plateau could be attributed to the equilibrium competition between forming of physical “cross-linking points” and independent globules depending on the copolymer solution concentrations.The formation of physical “cross-linking points” causes the thermothickening phenomenon or gelation in higher concentration at human body temperature, while the formation of independent globule causes the thermothinning phenomenon in lower concentration at the temperature higher than LCST of PNIPAM-g-PEO copolymer.
Keywords: Physical gelation; Network; PNIPAM; PEO; Copolymer; Viscosity;

Large-scale synthesis of tungsten oxide nanofibers by electrospinning by Xiaofeng Lu; Xincai Liu; Wanjin Zhang; Ce Wang; Yen Wei (996-999).
We show in this communication that large-scale synthesis of orthorhombic WO3 nanofibers can be obtained via a simple electrospinning method. The morphology and the crystal structure are investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), FTIR, X-ray diffraction patterns (XRD) and X-ray photoelectron spectra (XPS) spectra. SEM and TEM images showed that the diameter of the obtained WO3 nanofibers is between 100 and 500 nm. The structure of the obtained WO3 nanofibers was characterized by FTIR, XRD, and XPS spectra. The photoluminescence of the obtained WO3 nanofibers were also investigated.An electrospinning method to the synthesis of tungsten oxide nanofibers has been developed. It has been shown that the fibers are uniformly composed of some grains, which are proved by TEM image.
Keywords: Electrospinning; Tungsten oxide nanofibers; Polyvinylpyrrolidone;

Dioctadecyldimethylammonium bromide (DODAB) is a double chain vesicle-forming cationic surfactant, whereas octa-ethyleneglycol mono-n-dodecyl ether (C12E8) is a single chain micelle-forming nonionic surfactant. At room temperature (ca. 22 °C) C12E8 molecules self-assemble in water as micelles while DODAB is insoluble. A mixture of DODAB and C12E8, however, can be soluble in water at room temperature depending on the relative amount of the compounds. We report the formation of small unilamellar vesicles (SUVs) by dialyzing at room temperature a mixture of 1.0 mM DODAB with 10 mM C12E8 in water. Extended bilayers are formed as well in equilibrium with vesicles. Such structures are viewed by a cryogenic transmission electron microscopy (cryo-TEM) image.Cryo-TEM image for DODAB/C12E8/water after two-week dialysis of the mixed DODAB/C12E8 (1.0 mM/10 mM) micelle solution. For the TEM analysis the sample was quickly cooled from room temperature, ca. 22 °C, as reported in Ref. [6]. Arrows indicate either vesicle (A) or extended bilayer (B) structures. Image scale: bar corresponds to 100 nm.
Keywords: Cationic vesicles; Mixed micelles; Surfactant removal method; Dioctadecyldimethylammonium bromide; Octa-ethyleneglycol mono-n-dodecyl ether; Cryo-TEM;