Journal of Colloid And Interface Science (v.285, #1)

Equilibrium interfacial tension at the liquid/liquid interfaces for two chelating metal ion extractants, 2-hydroxy-5-nonylacetophenone oxime (HNAF) and 1-phenyldecane-1,3-dion (β-diketone), two solvating extractants, trioctylphosphine oxide (TOPO) and tributyl phosphate (TBP), and a modifier, decanol, were obtained with a drop volume tensiometer. Moreover, four equimolar binary mixtures of extractant/extractant and extractant/modifier type were considered. The composition of the mixed adsorbed monolayer and the molecular interaction parameters β were determined by the Rosen equation. It was found that in all the studied systems coadsorption exists; however, synergism in the reduction of interfacial tension was not observed. The obtained results indicate that in the case of three mixtures considered the composition of a mixed monolayer at the hydrocarbon/water interface was quite different from that in the bulk organic phase. Only for the TOPO/β-diketone mixture were the compositions at the interface and in the bulk organic phase similar. The obtained results indicate that it is impossible to predict the composition of a mixed monolayer by taking into account the interfacial activity of individual components of the mixture. In some cases the compound shows lower interfacial activity (smaller efficiency and effectiveness of adsorption) and occupies a dominant position at the interface, regardless of the type of hydrocarbon used as the organic diluent.
Keywords: Liquid/liquid interface; Mixed monolayer; Binary adsorption; Molecular interaction parameters β; Metal ion extractants;

The aim of this study was to carry out kinetic, thermodynamic, and surface characterization of the sorption of Cs+ ions on natural minerals of kaolinite and clinoptilolite. The results showed that sorption followed pseudo-second-order kinetics. The activation energies were 9.5 and 13.9 kJ/mol for Cs+ sorption on kaolinite and clinoptilolite, respectively. Experiments performed at four different initial concentrations of the ion revealed that the percentage sorption of Cs+ on clinoptilolite ranged from 90 to 95, compared to 28 to 40 for the kaolinite case. At the end of a 1 week period, the percentage of Cs+ desorption from clinoptilolite did not exceed 7%, while it amounted to more than 30% in kaolinite, indicating more stable fixation by clinoptilolite. The sorption data were best described using Freundlich and D–R isotherm models. Sorption showed spontaneous and exothermic behavior on both minerals, with Δ H 0 being −6.3 and − 11.4  kJ / mol for Cs+ uptake by kaolinite and clinoptilolite, respectively. Expanding the kaolinite interlayer space from 0.71 to 1.12 nm using DMSO intercalation, did not yield a significant enhancement in the sorption capacity of kaolinite, indicating that the surface and edge sites of the clay are more energetically favored. EDS mapping and elemental analysis of the surface of kaolinite and clinoptilolite revealed more intense signals on the surface of the latter with an even distribution of sorbed Cs+ onto the surfaces of both minerals.
Keywords: Kaolinite; Clinoptilolite; Cs+; Sorption;

Supramolecular structures on silica surfaces and their adsorptive properties by Vladimir N. Belyakov; Lyudmila A. Belyakova; Anatoly M. Varvarin; Olexandra V. Khora; Sergei L. Vasilyuk; Konstantin A. Kazdobin; Tetyana V. Maltseva; Alexey G. Kotvitskyy; Angela F. Danil de Namor (18-26).
The study of adsorptive and chemical immobilization of β-cyclodextrin on a surface of hydroxylated silicas with various porous structure is described. Using IR spectroscopy, thermal gravimetrical analysis with a programmed heating, and chemical analysis of the silica surface, it is shown that the process of adsorption–desorption of β-cyclodextrin depends on the porous structure of the silica. The reaction of esterification was used for chemical grafting of β-cyclodextrin on the surface of hydroxylated silicas. Hydrolytic stability of silicas chemically modified by β-cyclodextrin apparently is explained by simultaneous formation of chemical and hydrogen bonds between surface silanol groups and hydroxyl groups of β-cyclodextrin. The uptake of the cations Cu(II), Cd(II), and Pb(II) and the anions Cr(VI) and As(V) by silicas modified with β-cyclodextrin is investigated as a function of equilibrium ion concentrations. The increase of ion uptake and selectivity of ion extraction in comparison with starting silicas is established. It is due to the formation of surface inclusion complexes of the “host–guest” type in which one molecule of β-cyclodextrin interacts simultaneously with several ions.
Keywords: Silica surface; β-Cyclodextrin; Adsorption; Reaction of esterification; IR spectroscopy; Uptake; Toxic metal ions;

Adsorption behavior of herbicide butachlor on typical soils in China and humic acids from the soil samples by Duanping Xu; Zhonghou Xu; Shuquan Zhu; Yunzhe Cao; Yu Wang; Xiaoming Du; Qingbao Gu; Fasheng Li (27-32).
Three kinds of soils in China, krasnozem, fluvo-aquic soil, and phaeozem, as well as the humic acids (HAs) isolated from them, were used to adsorb the herbicide butachlor from water. Under the experimental conditions, the adsorption amount of butachlor on soils was positively correlated with the content of soil organic matter. HAs extracted from different kinds of soils had different adsorption capacity for the tested herbicide, which was positively correlated with their content of carbonyls. The adsorption mechanism was studied using Fourier transform infrared spectroscopy and cross-polarization with magic angle spinning 13C nuclear magnetic resonance (CP-MAS 13C NMR) techniques. It was showed that the adsorption mainly took place on the C=O, phenolic and alcoholic O―H groups of HAs. It was also confirmed that the adsorption mechanism was hydrogen bonds formation between the above groups of HAs and butachlor molecules.
Keywords: Herbicide butachlor; Adsorption; Typical soils; Humic acids;

Adsorption of cationic polyelectrolyte, a homopolymer of maleimide propyl trimethylammonium chloride (MPTMAC), on silica nanoparticles from aqueous solution was studied. The adsorbed amount of MPTMAC and the adsorption layer thickness from solutions of different pH, polyelectrolyte concentration, salt type, and salt concentration were measured. The adsorbed amount exhibited a maximum as a function of the electrolyte concentration. The onset of the decline in the adsorbed amount depended on the type of counterions. The thickness of the adsorption layer increased gradually with increased of electrolyte concentration and leveled off at high electrolyte concentration. The enhanced adsorption in the presence of Na2SO4 can be explained by the bivalent SO2− 4 causing a better shielding effect. With increasing pH the adsorbed amount of MPTMAC increased, whereas the thickness of an adsorbed layer of MPTMAC decreased. At low polyelectrolyte concentrations unstable silica suspensions were observed from a stability test. At high polyelectrolyte concentrations the higher particle coverage caused electrosteric stabilization of the dispersion. However, further increase in MPTMAC concentration after saturated adsorption would flocculate the dispersed system. At low pH, MPTMAC tending to create a loops or tails conformation stabilized the suspension.
Keywords: Adsorption; Polyelectrolyte; Dispersion; Silica;

Particle and surface characterization of a natural illite and study of its copper retention by Ramón A. Alvarez-Puebla; David S. dos Santos; Carolina Blanco; Jesús C. Echeverria; Julián J. Garrido (41-49).
Illite clays are known to have a strong affinity for metallic pollutants in the environment and can be applied as low-cost adsorbents for industrial waste treatment. A crucial factor in the development of such applications, however, is the understanding of the chemical, mineralogical, and colloidal properties of these clays. It is also important to understand the mechanisms involved in the surface adsorption of metals by these adsorbants. In order to study the retention of transition metals on illite clays, we have applied surface characterization techniques such as FPIA, SEM-EDX, XRD, N2 (77 K) adsorption, and FTIR. In addition to these experimental techniques, we have also employed a theoretical model that accounts for the chemistry of transition metal ions, and considers the global retention process to be the sum of several single retention processes. This model adequately fits the experimental data and allows for the speciation of metal retention on illite surfaces. Between pH values of 2.53 and 3.01 the only adsorption processes are the electrostatic sorption of [Cu(H2O)6]2+, and the surface complexation of [Cu(H2O)6]2+ and [Cu(OH)(H2O)5]+ ions. Surface complexation of [Cu(OH)(H2O)5]+ ions increases with pH, overcoming [Cu(H2O)6]2+ retention, and thus contributing to the surface precipitation of Cu(OH)2.
Keywords: Illite; SEM; Flow particle image analysis; Gas adsorption; Cu(II); Isotherm modeling;

Natural vermiculite as an exchanger support for heavy cations in aqueous solution by Maria G. da Fonseca; Michelle M. de Oliveira; Luiza N.H. Arakaki; José G.P. Espinola; Claudio Airoldi (50-55).
The natural highly charged lamellar silicate vermiculite was investigated as an exchanger matrix in doubly distilled water solution to exchange magnesium inside the lamella with the heavy cations copper, nickel, cobalt, and lead at the solid/liquid interface. The extension of each exchange reaction was dependent on time of reaction, pH, and cation concentration. The maximum time presented the following order Pb2+  < Ni2+  < Cu2+  < Co2+, which corresponds to 12, 24, 48, and 72 h, respectively. The best performance was observed for nickel, as represented by the exchange capacity N f , which gave values 0.59, 0.76, 0.84, and 0.93 mmol g−1 for Pb2+  < Co2+  < Cu2+  < Ni2+, respectively. This capacity is dependent on pH interval variation from 1 to 9, being significantly increased in alkaline condition. The isotherm data were adjusted to a modified Langmuir equation and from the data the spontaneous Gibbs free energy was calculated. Linear correlations were obtained through Gibbs free energy or the maximum capacity against the cationic radius plot, with the lowest values for the largest cation lead. An exponential correlation was also observed for the maximum capacity versus enthalpy of hydration plot, indicating a difficulty of the less hydrated cation, lead, in exchanging with magnesium inside the lamellar space, as suggested by the proposed mechanism. The saturated matrices with cations presented a decrease in interlayer distance in comparison with the original vermiculite, which can be related to the hydrated phases, characteristic for each cation, with a lowest value for lead.
Keywords: Ionic exchanger; Vermiculite; Clays; Heavy ions;

Water vapor adsorption on activated carbon preadsorbed with naphtalene by T. Zimny; G. Finqueneisel; L. Cossarutto; J.V. Weber (56-60).
The adsorption of water vapor on a microporous activated carbon derived from the carbonization of coconut shell has been studied. Preadsorption of naphthalene was used as a tool to determine the location and the influence of the primary adsorbing centers within the porous structure of active carbon. The adsorption was studied in the pressure range p / p 0 = 0 – 0.95 in a static water vapor system, allowing the investigation of both kinetic and equilibrium experimental data. Modeling of the isotherms using the modified equation of Do and Do was applied to determine the effect of preadsorption on the mechanism of adsorption.
Keywords: Activated carbon; Naphthalene preadsorption; Water adsorption; Isotherm modelling;

Wetting fibers with liposomes by N. Borghi; K. Alias; P.-G. de Gennes; F. Brochard-Wyart (61-66).
Giant unilamellar vesicles (GUVs) are deposited on glass microfibers. The vesicles adopt the classical “onduloidal” shape of liquid droplets on fibers. They spread by two simultaneous mechanisms: envelopment and emission of a precursor film. This film spreads faster than on a uniform plane surface and eventually stops, signaling the presence of defects on the rod. This fast spreading tenses the vesicles; transient pores open on the GUVs and the internal liquid leaks out. This process leads to a new technique for fiber coating.

A stable monolayer of N-octadecylaniline containing stearic acid at the air–water interface has been obtained. However, the Langmuir monolayer of pure poly(N-octadecylaniline) was not stable, but mixed Langmuir–Blodgett films of this polymer with stearic acid in different ratios as a spreading aid were stable. The electrical conductivity of these films increased by five orders of magnitude after doping with iodine as compared to that before iodine doping ( 5.8 × 10 −7  S cm −1 ) . Temperature-dependent electrical conductivity suggested that these films were semiconducting in nature with low thermal activation energy. Impedance analyses of these films revealed that the equivalent circuit for poly(N-octadecylaniline) was (RQ) whereas that for mixed poly(N-octadecylaniline) with stearic acid was (RQ)(RQ).
Keywords: Poly(N-octadecylaniline); Langmuir–Blodgett films; Semiconductor; Impedance analysis;

In this work, we aimed to study the association and interaction behavior of poly(ethylene oxide)–b–poly(propylene oxide)–b–poly(ethylene oxide) block copolymers grafted with poly(vinylpyrrolidone). Critical micellization concentrations were determined using fluorescent probes (pyrene) and critical micellization temperatures characterizing temperature-dependent transitions from monomers to multimolecular micelles were measured. The thermal responsiveness of the copolymer is not affected by the grafting. The hydrodynamic radius of the graft copolymer micelles is found to be greater than that of the original copolymer micelles. The graft copolymer is found to form anisotropic aggregates. The structure of the graft copolymer micelles is less disrupted by the anionic surfactant sodium dodecyl sulfate, compared to the ungraft copolymer.
Keywords: Block copolymers; Free radical polymerization; Graft copolymer; Pluronic;

Pluronic poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (PEO–PPO–PEO) block copolymers are grafted with poly(vinyl pyrrolidone) by free radical polymerization of vinyl pyrrolidone with simultaneous chain transfer to the Pluronic in dioxane. This modified polymer has both thermal responsiveness and remarkable capacity to interact with a wide variety of hydrophilic and hydrophobic pharmaceutical agents which is very attractive for medical applications. The chemical structure of the graft copolymers was characterized by FTIR and 1H NMR spectroscopy. Polymerization conditions such as initiators, feed ratio, and reaction times are studied to obtain the ideal graft copolymer.
Keywords: Block copolymers; Radical polymerization; FTIR;

Homogeneous forced hydrolysis of aluminum through the thermal decomposition of urea by R.J.M.J. Vogels; J.T. Kloprogge; J.W. Geus (86-93).
Homogeneous hydrolysis of aluminum by decomposition of urea in solution was achieved because the urea coordinates to the Al3+ in solution, forming [Al(H2O)5(urea)]3+ and to a lesser extent [Al(H2O)4(urea)2]3+. Upon hydrolysis more hydrolyzed monomeric species, [Al(H2O)5(OH)]2+, [Al(H2O)4(OH)2]+, [Al(H2O)4(urea)(OH)]2+, and [Al(H2O)3(urea)(OH)2]+, were formed, followed by trimeric species and the Al13 Keggin complex [AlO4Al12(OH)24(H2O)12]7+. The 27Al NMR spectra indicated the formation of other complexes in addition to the Al13 at the end of the hydrolysis reaction.
Keywords: Al13; Keggin structure; Hydrolysis; Nuclear magnetic resonance spectroscopy; Urea;

Model cellulose films exposed to H. insolens glucoside hydrolase family 45 endo-cellulase—the effect of the carbohydrate-binding module by Jonny Eriksson; Martin Malmsten; Fredrik Tiberg; Thomas Hønger Callisen; Ture Damhus; Katja S. Johansen (94-99).
The effects of enzyme structure and activity on the degradation of model cellulose substrates were investigated by ellipsometry for the cellulase Humicola insolens GH45. The inactive variant D10N was found to adsorb at the cellulose surface but also to be incorporated into the cellulose films to an extent that depended on pH. For the native protein, the initial adsorption monitored for the inactive variant D10N was followed by enzyme-mediated degradation of the cellulose films. Again, a dependence on pH was found, such that higher pH resulted in slower enzymatic degradation. Removing the carbohydrate-binding module eliminated this pH dependence but also resulted in a decreased adsorption to the cellulose surface, and in a decreased net catalytic effect.
Keywords: Ellipsometry; Cellulose model surface; Spin coating; Adsorption; Cellulase; Enzymatic degradation;

Effect of thermal treatment on interfacial properties of β-lactoglobulin by Dennis A. Kim; Michel Cornec; Ganesan Narsimhan (100-109).
The changes in the secondary conformation and surface hydrophobicity of β-lactoglobulin subjected to different thermal treatments were characterized at pH values of 7, 5.5 and 4 using circular dichroism (CD) and hydrophobic dye binding. Heating resulted in a decrease in α-helix content with a corresponding increase in random coil at all pH values, this change being more pronounced for small heating times. Heating also resulted in an increase in surface hydrophobicity as a result of partial denaturation, this increase being more pronounced at pH 4. Thermal treatment resulted in a shift of the spread monolayer isotherm at air–water interface to smaller area per molecule due to increased flexibility and more loop formation. Thermal treatment led to an increase in interfacial shear elasticity and viscosity of adsorbed β-lactoglobulin layer at pH 5.5 and 7. Interfacial shear elasticity, shear viscosity, stability of β-lactoglobulin stabilized emulsion and average coalescence time of a single droplet at a planar oil–water interface with adsorbed protein layer exhibited a maximum for protein subjected to 15 min heat treatment at pH 7. At pH 5.5, the interfacial shear rheological properties and average single drop coalescence time were maximum for 15 min heat treatment whereas emulsion stability was maximum for 5 min heat treatment. At pH 7, thermal treatment was found to enhance foam stability. Analysis of thin film drainage indicated that interfacial shear rheological properties do not influence thin film drainage.
Keywords: β-Lactoglobulin; Secondary conformation; Surface hydrophobicity; Thermal treatment; Partial denaturation; Emulsion stability; Interfacial shear elasticity; Interfacial shear viscosity; Drop coalescence; Spread monolayer isotherm;

The kinetics of the interaction between Gemcitabine (a new anticancer drug) and phospholipid membrane models was investigated. This kind of study is of particular importance both in hypothesizing the interaction of Gemcitabine with mammalian cell membranes and in evaluating the potentiality of liposomes as a Gemcitabine delivery system. Unilamellar (LUV) and multilamellar (MLV) membrane models were made up of dimyristoylphosphatidylcholine (DMPC), dimyristoylphosphatidic acid sodium salt (DMPA), or a DMPC–DMPA mixture (1:1 molar ratio). Gemcitabine–phospholipid vesicle interaction was studied by differential scanning calorimetry (DSC) measurements performed at different time intervals. The findings showed slower permeation kinetics of Gemcitabine through MLV than LUV which, at the same lipid/water ratio, are characterized by a larger lipid surface in contact with the drug aqueous solution. Another interesting difference between LUV and MLV is the onset of a transient two-peak structure during the DSC scans of MLVs. The effect is due to the unequal distribution of the drug between the outer and inner bilayers of the multilamellar vesicles during the permeation kinetics. At equilibrium the two-peak structure merges into a unique peak. This finding may provide useful information about the lipid bilayer permeability in model membranes.
Keywords: Differential scanning calorimetry; Gemcitabine; Phosphatidyc acid; Phosphatidylcholine; Membranes;

Penetration and interactions of the antimicrobial peptide, microcin J25, into uncharged phospholipid monolayers by Augusto Bellomio; Rafael G. Oliveira; Bruno Maggio; Roberto D. Morero (118-124).
Microcin J25 forms stable monolayers at the air–water interface showing a collapse at a surface pressure of 5 mN/m, 220 mV of surface potential, and 6 fV per squared centimeter of surface potential per unit of molecular surface density. The adsorption of microcin J25 from the subphase at clean interfaces leads to a rise of 10 mN/m in surface pressure and a surface potential of 220 mV. From these data microcin appears to be a poor surfactant per se. Nevertheless, the interaction with the lipid monolayer further increase the stability of the peptide at the interface depending on the mode in which the monolayer is formed. Spreading with egg PC leads to nonideal mixing up to 7 mN/m, with hyperpolarization and expansion of components at the interface, with a small excess free energy of mixing caused by favorable contributions to entropy due to molecular area expansion compensating for the unfavorable enthalpy changes arising from repulsive dipolar interactions. Above 7 mN/m microcin is squeezed out, leaving a film of pure phospholipid. Nevertheless, the presence of lipid at 10 and 20 mN/m stabilize further microcin at the interface and adsorption from the subphase proceeds up to 30 mN/m, equivalent to surface pressure in bilayers.
Keywords: Langmuir monolayers; Gibbs monolayers; Microcin; Phosphatidyl choline; MccJ25; Antimicrobial peptide;

Atomic force microscopy measurement of the elastic properties of the kidney epithelial cells by Y. Rabinovich; M. Esayanur; S. Daosukho; K. Byer; H. El-Shall; S. Khan (125-135).
Direct interaction force measurements using atomic force microscopy (AFM) were carried out between a silicon nitride tip and renal epithelial cells (Madin-Darby Canine Kidney-MDCK and proximal tubular epithelial cells derived from pig kidneys, LLC-PK1). The approaching (extending) portion of the force/distance curves is considered, and repulsive forces in the long range of 2–3 μm were seen in both MDCK as well as LLC-PK1 cells growing under normal conditions. The repulsive force in the shorter distance range of 50–200 nm was also observed, when cells were damaged exposing the underlying basal membrane. LLC-PK1 cells were more prone to damage than the MDCK cells, hence short-range forces were common in the former and long-range forces in the latter cells. The functional dependence of repulsive force on the indentation depth changes, at small indentation depth the force increases linearly, while at larger indentations the force is a quadratic function of the distance, which is attributed to the elasticity of the membrane and the solid-like response of cells, respectively. The oxalate treatment of cells for 2–4 h gives rise to an increase in the elastic modulus of the cells.
Keywords: Atomic force microscopy; Elastic properties; Kidney epithelial cells;

Characterizations and properties of hairy latex particles by Pascal Borget; Françoise Lafuma; Cécile Bonnet-Gonnet (136-145).
Industrial latex composed of a hydrophobic core surrounded by a charged hydrophilic layer exhibits excellent stability toward monovalent salt. That feature is classically attributed to a steric effect due to a loss of entropy during overlapping of coating materials. The so-called electrosteric stabilization is, however, not a straightforward function of the nature of the hydrophilic corona. This suspension was characterized in dilute solution by scattering and electrophoresis techniques. In contrast to spherical brushes the interface between the core and the corona is not well defined. The layer is more similar to a highly hydrated nonuniform gel with few longer strands that control the hydrodynamic properties than to a polyelectrolyte brush whose dependence on ionic strength reflects the concentration of counterions inside a well-defined structure. Thus the steric contribution to stabilization of these hairy particles appears to be insignificant in the range studied. The highly hydrated nature and the global charge of the layer are two predominant factors for the stability of the particles.
Keywords: Electrosteric stabilization; Hairy latex; Core–corona particles; Spherical brushes; Electrophoretic mobility; Dynamic light scattering; Small-angle neutron scattering;

A simple and controlled method of preparing uniform Ag midnanoparticles on Tollens-soaked silica spheres by Zhimin Chen; Xin Chen; Linli Zheng; Tian Gang; Tieyu Cui; Kai Zhang; Bai Yang (146-151).
Ag midnanoparticles (midnanoparticles are those particles whose diameters are in the range from 20 to 80 nm) with average size of 30–50 nm and tunable packing densities were formed on the surface of preformed Tollens-soaked silica spheres by a simple and controlled method. The process mainly involved two steps. In the first step the absorption of Ag(NH3)+ 2 ions occurred on the silica spheres and in the second step Ag(NH3)+ 2 ions on the silica spheres were reduced to Ag midnanoparticles in the presence of glucose solution. The amount of Ag midnanoparticles on the silica spheres could easily be tuned by varying the washing times in the process of preparing the Tollens-soaked silica spheres. The washing process also effectively avoided the reduction of Ag(NH3)+ 2 ions and the nucleation of Ag particles in solution and easily produced more uniform Ag midnanoparticles on the silica spheres. Attributing to the uniform Ag midnanoparticles, the Ag midnanoparticle-coated silica spheres show unique optical properties in the UV–vis absorption spectra. The resulting Ag midnanoparticle-coated silica spheres were characterized with transmission electron microscopy, UV–vis–IR recording spectrophotometry, and X-ray photoelectron spectroscopy.

Gel trapping of dense colloids by Peter B. Laxton; John C. Berg (152-157).
Phase density differences in sols, foams, or emulsions often lead to sedimentation or creaming, causing problems for materials where spatial uniformity over extended periods of time is essential. The problem may be addressed through the use of rheology modifiers in the continuous phase. Weak polymer gels have found use for this purpose in the food industry where they appear to be capable of trapping dispersoid particles in a three-dimensional matrix while displaying water-like viscosities at low shear. Attempts to predict sedimentation stability in terms of particle properties (size, shape, density difference) and gel yield stress have led to qualitative success for suspensions of large particles. The effect of particle size, however, in particular the case in which colloidal dimensions are approached, has not been investigated. The present work seeks to determine useful stability criteria for colloidal dispersions in terms of readily accessible viscoelastic descriptors. Results are reported for systems consisting of 12 μm poly(methyl methacrylate) (PMMA) spheres dispersed in aqueous gellan gum. Monovalent salt concentration is varied to control rheological properties, and sedimentation/centrifugation experiments are performed to determine dispersion stability. Necessary conditions for stability consist of a minimum yield stress together with a value of tan δ less than unity.
Keywords: Gel trapping; Sedimentation stability; Gellan gum; Rheology; Yield stress;

Dendrimer-protected TiO2 nanoparticles were synthesized by hydrolysis of TiCl4 in solutions of poly(amido amine) dendrimers (64 terminals) under cooling. The morphology of dendrimers surrounding TiO2 nanoparticles depended on the terminal groups (amine, carboxyl, hydroxy) of dendrimers. The size (4.4–6.7 nm) of dendrimer-protected TiO2 nanoparticles was slightly smaller than that (7.5 nm) of bare TiO2 nanoparticles. The photodegradation of 2,4-dichlorophenoxyacetic acid revealed that dendrimer-protected TiO2 nanoparticles are more active as a photocatalyst than TiO2 nanoparticles without protectors. This suggests that the dendrimer acts as a reservoir of photoreacting reagents besides acting as a protector of nanoparticles.
Keywords: TiO2; Nanoparticles; Dendrimer; Poly(amido amine) dendrimer; Photodegradation; 2,4-Dichlorophenoxyacetic acid; Photocatalysis;

Nanofibers of LiMn2O4 by electrospinning by Na Yu; Changlu Shao; Yichun Liu; Hongyu Guan; Xinghua Yang (163-166).
Through sol–gel processing and electrospinning technique, extrathin fibers of poly(vinyl alcohol) (PVA)/lithium chloride/manganese acetate composite fibers were prepared. After calcination of the above precursor fibers at 600 °C, the spinel lithium manganese oxide (LiMn2O4) nanofibers, with a diameter of 100–200 nm, were successfully obtained. The fibers were investigated by TG–DTA, XRD, FT-IR, and SEM, respectively. The results showed that the crystalline phase and morphology of the fibers were largely influenced by the calcination temperature.
Keywords: LiMn2O4; Nanofibers; Electrospinning; Sol–gel processing; PVA;

CFD simulation of shear-induced aggregation and breakage in turbulent Taylor–Couette flow by Liguang Wang; R. Dennis Vigil; Rodney O. Fox (167-178).
An experimental and computational investigation of the effects of local fluid shear rate on the aggregation and breakage of ∼ 10   μm latex spheres suspended in an aqueous solution undergoing turbulent Taylor–Couette flow was carried out. First, computational fluid dynamics (CFD) simulations were performed and the flow field predictions were validated with data from particle image velocimetry experiments. Subsequently, the quadrature method of moments (QMOM) was implemented into the CFD code to obtain predictions for mean particle size that account for the effects of local shear rate on the aggregation and breakage. These predictions were then compared with experimental data for latex sphere aggregates (using an in situ optical imaging method). Excellent agreement between the CFD-QMOM and experimental results was observed for two Reynolds numbers in the turbulent-flow regime.
Keywords: Computational fluid dynamics; Aggregation; Breakage; Taylor–Couette flow; QMOM;

Colloidal particles and biological cells are patterned and separated laterally adjacent to a micropatterned electrode array by applying AC electric fields that are principally oriented normally to the electrode array. This is demonstrated for yeast cells, red blood cells, and colloidal polystyrene particles of different sizes and ζ-potentials. The separation mechanism is observed experimentally to depend on the applied field frequency and voltage. At high frequencies, particles position themselves in a manner that is consistent with dielectrophoresis, while at low frequencies, the positioning is explained in terms of a strong coupling between gravity, the vertical component of the dielectrophoretic force, and the Stokes drag on particles induced by AC electroosmotic flow. Compared to high frequency dielectrophoretic separations, the low frequency separations are faster and require lower applied voltages. Furthermore, the AC electroosmosis coupling with dielectrophoresis may enable cell separations that are not feasible based on dielectrophoresis alone.
Keywords: Dielectrophoresis; AC electroosmosis; Induced dipole strength; Microelectrode array; Colloidal particles;

Application of the thin-layer wicking (TLW) technique on powdered minerals is useful for characterizing their surfaces. Albite (Na-feldspar) and orthoclase (K-feldspar) are feldspar minerals which are frequently found in the same matrix. Despite similarities in their physicochemical properties, separation of these minerals from each other by flotation is generally possible in the presence of monovalent salts such as NaCl. Both albite and orthoclase exhibit the same microflotation properties and rather close electrokinetic profiles in the absence of salt. In this study, contact angles of albite and orthoclase determined by the TLW technique yielded close values in the absence and presence of amine collector. While the calculated surface energies and their components determined using contact angle data reveal that the energy terms remain farther apart in the absence of the collector, the differences narrow down at collector concentrations where full flotation recoveries are obtained. However, the effect of addition of NaCl on contact angles and surface free energy components at constant amine concentration indicates that albite is significantly affected by salt addition, whereas orthoclase remains marginally affected. This interesting finding is explained on the basis of ion-exchange properties, the stability of the interface, flotation data, and zeta potential data in the presence of NaCl.
Keywords: Feldspar; Thin-layer wicking method; Surface energies; Contact angle; Flotation;

Fe3Al and Cr18-Ni8 stainless steel were diffusion-bonded in vacuum and a Fe3Al/Cr18-Ni8 interface with reaction layer was formed. Microstructure in the reaction layer at Fe3Al/Cr18-Ni8 interface was analyzed by means of scanning electron microscope (SEM) and electron probe micro-analyzer (EPMA). The growth of reaction layer with heating temperature (T) and holding time (t) was researched. The results indicate that FeAl, Fe3Al, Ni3Al, and α-Fe (Al) solid solution are formed in the reaction layer. These phases are favorable to promote the element diffusion and to accelerate the formation of the reaction layer at Fe3Al/Cr18-Ni8 interface. The growth of reaction layer obeys the parabolic law and its thickness (X) is expressed by X 2 = 7.5 × 10 −4 exp ( − 83.59 / R T ) ( t − t 0 ) .
Keywords: Fe3Al/Cr18-Ni8 interface; Diffusion bonding; Reaction layer; Characteristics;

Characterisation of the protolytic properties of synthetic carbonate free fluorapatite by Mathias Jarlbring; Lars Gunneriusson; Willis Forsling (206-211).
The acid/base surface properties of carbonate free fluorapatite (Ca5(PO4)3F) have been characterised using high precision potentiometric titrations and surface complex modelling. Synthetic carbonate free fluorapatite was prepared and characterised by SEM, XRD, FT-IR and FT-Raman. The specific surface area was determined to be 17.7 ± 1.2   m 2 g −1 with BET (N2 adsorption). The titrations were performed at 25 ± 0.2  °C , within the pH range 5.7–10.8, in 0.10 and 0.50 mol dm−3 NaNO3 ionic media. Experimental data were interpreted using the constant capacitance model and the software FITEQL 4.0. The surface equilibria: S1OH ⇄S1O + H+ lg β −110 s (int), S2OH ⇄S2O + H+ lg β −101 s (int) well describes the surface characteristics of synthetic fluorapatite. The equilibrium constants obtained were: lg β −110 s ( int ) = − 6.33 ± 0.05 and lg β −101 s ( int ) = − 8.82 ± 0.06 at I = 0.10   mol dm −3 . At the ionic strength 0.50 mol dm−3, the equilibrium constants were slightly shifted to: lg β −110 s ( int ) = − 6.43 ± 0.05 and lg β −101 s ( int ) = − 8.93 ± 0.06 . The number of active surface sites, N s , was calculated from titration data and was found to be 2.95 and 2.34 sites nm−2 for the ionic strengths 0.10 and 0.50 mol dm−3, respectively. pHPZC or the IEP was found to be 5.7 from Z-potential measurements.
Keywords: Synthetic fluorapatite; Acid/base properties; Potentiometric titrations; Constant capacitance modelling; FT-IR; XRD;

Surface complex characteristics of synthetic maghemite and hematite in aqueous suspensions by Mathias Jarlbring; Lars Gunneriusson; Björn Hussmann; Willis Forsling (212-217).
The acid–base properties of the maghemite (γ-Fe2O3)/water and hematite (α-Fe2O3)/water interfaces have been studied by means of high precision potentiometric titrations and the experimental results are evaluated as surface complexation reactions. Synthetic maghemite and hematite were prepared and characterized using a combination of SEM, FT-IR and XRD. The specific surface area of the minerals was determined by the BET method. The titrations were performed at 25.0 ± 0.2 ° C within the range 2.8 < pH < 8.5 , NaNO3 ionic medium giving total ionic strengths of 0.10 and 0.50 mol dm−3 in both systems. Experimental data were evaluated using the constant capacitance model. The total proton exchange capacities of the solids were determined by saturation of the surfaces with excess acid. The number of protonated surface sites per nm2 was found to be 0.81 ± 0.05 and 1.03 ± 0.04 for maghemite, at I = 0.10 and 0.50 mol dm−3, respectively. The IEP for maghemite was determined from the ζ-potential using a Zetasizer 4 instrument.
Keywords: Maghemite; Hematite; Characterization; Potentiometric titrations; Surface complex modeling; Constant capacitance;

Temperature-programmed reduction (TPR), oxidation (TPO), and desorption (TPD) studies were performed on three copper–ceria mixed oxide samples having the same nominal composition, Cu0.15Ce0.85O2−y , but prepared in three different ways: by co-precipitation, the sol–gel peroxide route, and the sol–gel citric acid route. The obtained results reveal that despite a drastic initial drop in specific surface area after consecutive redox cycles, the hydrogen consumption remains constant. This is because CuO is highly dispersed over the surface of CeO2 nanocrystallites and remains highly dispersed even after the agglomeration of CeO2 nanocrystallites in a denser secondary structure. The dispersed CuO is reduced to Cu0 during the TPR, forming agglomerated metal particles on the surface of partially reduced CeO2. However, after subsequent temperature-programmed oxidation all the Cu0 is oxidized back into CuO and redispersed over the CeO2 crystallites.
Keywords: Catalyst; Cu0.15Ce0.85O2−y ; Synthesis; XRD; Redox properties; H2; O2; TPR; TPO; TPD;

A novel method to fabricate semipermeable cellulose membranes based on cellulose regeneration of a dry membrane cast by the neutralization reaction is presented in this paper. In this method, an environmentally acceptable cellulose dissolution procedure is employed to prepare the membrane casting solution comprised of microcrystalline cellulose dissolved in aqueous NaOH. Moreover, a new cast drying/cellulose regeneration technique is proposed and successfully applied to prepare membranes after the exploitation of the conventional immersion precipitation method, which results in the formation of granular cellulose particles rather than membranes due to the low cellulose concentration ( < 5  wt% ) in the cast. In the present technique, the cellulose concentration in the membrane cast is dramatically increased through water evaporation, and glycerin is utilized in the cellulose regeneration process to achieve a gentle neutralization reaction. As a result, defect-free membranes with a uniform structure are developed. A detailed investigation is also presented concerning the effects of membrane forming parameters, i.e., the concentrations of cellulose, solvent, and acid, and the membrane thickness, on membrane properties. In addition, by coordinating the molecular separation experiments via the ultrafiltration process against a number of macromolecules with various molecular weights, the fabricated membranes are demonstrated to be capable of sieving molecules with a MW above 50,000.
Keywords: Cellulose membrane; Membrane fabrication; Microcrystalline cellulose; Cellulose regeneration; Water flux; Solute rejection;

The formation of todorokite-type manganese oxide (TodMO) by hydrothermal soft chemical reaction (Mg2+ exchange followed by hydrothermal treatment) was studied using three kinds of Na-type birnessite (Na-BirMO) with different crystallinities. Buserite (BusMO) formation by Mg2+ exchange and TodMO formation by hydrothermal treatment progressed in a similar manner regardless of the crystallinity of the initial Na-BirMO, but the crystallinity of the synthesized TodMO depended on that of the initial Na-BirMO. Particle morphology of the synthesized TodMO was related to the crystallinity of the initial Na-BirMO. The amounts of fibrous morphology were gradually increasing, accompanied by increased crystallinity of the initial Na-BirMO. TodMO with a neat fibrous morphology was obtained using a high crystalline Na-BirMO as precursor. Most of the interlayer metal ions (Na+ and Mg2+) were extracted from Na-BirMO and BusMO by treatment with a 0.1 M HCl solution, while only 37% of Mg2+ was extracted from TodMO. Both the acid treatment and the particle morphology may be the most convenient method to distinguish TodMO from BusMO.
Keywords: Tunnel manganese oxide; Layered manganese oxide; Hydrothermal treatment; Particle morphology; Particle crystallinity;

Ion transfer across ion-exchange membranes with homogeneous and heterogeneous surfaces by E. Volodina; N. Pismenskaya; V. Nikonenko; C. Larchet; G. Pourcelly (247-258).
A homogeneous (AMX) and two heterogeneous (MA-40, MA-41) anion-exchange membranes, as well as a heterogeneous cation-exchange membrane (MK-40), are studied by electronic scanning microscopy, voltammetry, and chronopotentiometry. The presence of conducting and nonconducting regions on the surfaces of heterogeneous membranes is established by means of element analysis. The fraction of conducting regions is found by an image treatment. The surface of the AMX membrane was partially coated with microspots of a paint to make it heterogeneous (AMXheter). Voltammetric and chronopotentiometric measurements for AMX, AMXheter, and MA-41 membranes in NaCl solutions are carried out and the pH changes in the solution layers adjoining to these membranes are recorded. Analysis of obtained results shows that the concentration polarization of studied membranes characterized by the potential drop and the rate of water dissociation at the interface is mainly governed by the properties of their surfaces. It is found that the local limiting current density through conducting regions of a heterogeneous membrane is several times higher than the average limiting current through a homogeneous membrane.
Keywords: Ion-exchange membrane; Surface heterogeneity; Electronic scanning microscopy; Mass transport; Voltammetry; Chronopotentiometry;

The functional layered organosilica materials prepared with anion surfactant templates by Ken Yao; Yusuke Imai; LiYi Shi; AiMei Dong; Yoshio Adachi; Keiko Nishikubo; Eiichi Abe; Hiroshi Tateyama (259-266).
A novel strategy for the synthesis of layered organosilica is demonstrated. The ionic interaction between the anionic group of a surfactant (sodium dodecyl sulfate) and the cationic organic group of an organosilane (3-aminopropyltrimethoxysilane, ATMS) under acidic conditions was utilized to create a layered organosilica at room temperature. The inorganic part of the organosilica layer was an Si–O hexagonal sheet, and organofunctional groups were alternately arranged on both sides of the sheet. The layered structure of the ATMS organosilica was retained after the removal of the surfactant with chloride anion. The properties of the layered ATMS organosilica were investigated. The layered ATMS–Cl organosilica is stable and possesses a definite layer structure in water or ethanol. Various kinds of anions can be intercalated in the interlayer space of the layered ATMS organosilicas and the layer was expanded dependent on the intercalated anions. The structure of the layered ATMS organosilica was well retained during the intercalation processes.
Keywords: Layered organosilica; Organosilane; Ionic interaction; Sodium dodecyl sulfate; Intercalation;

In this work, the effect of atmospheric-pressure plasma treatments on surface properties of polyimide film are investigated in terms of X-ray photoelectron spectroscopy (XPS), contact angles, and atomic force microscopy (AFM). The adhesion characteristics of the film are also studied in the peel strengths of polyimide/copper film. As experimental results, the polyimide surfaces treated by plasma lead to an increase of oxygen-containing functional groups or the polar component of the surface free energy, resulting in improving the adhesion characteristics of the polyimide/copper foil. Also, the roughness of the film surfaces, confirmed by AFM observation, is largely increased. These results can be explained by the fact that the atmospheric-pressure plasma treatment of polyimide surface yields several oxygen complexes in hydrophobic surfaces, which can play an important role in increasing the surface polarity, wettability, and the adhesion characteristics of the polyimide/copper system.
Keywords: Polyimide; Atmospheric-pressure plasma; Surface properties; Surface morphology; Adhesion characteristics;

Two sets of composite membranes having an asymmetric sulfonated polysulfone membrane as support layer have been obtained and electrically characterized (membranes SPS–PEG and PA–LIGS). The skin layer of the membrane SPS–PEG contains different percentages of polyethylene glycol in the casting solution (5, 25, 40, and 60 wt%), while lignosulfonate was used for manufacturing PA–LIGS membranes (5, 10, 20, and 40 wt%). Membrane electrical characterization was done by means of impedance spectroscopy (IS) measurements, which were carried out with the membranes in contact with NaCl solutions at different concentrations ( 10 −3 ⩽ c ( M ) ⩽ 5 × 10 −2 ) . Electrical resistance and equivalent capacitance of the different membrane samples were determined from IS plots by using equivalent circuits as models. Results show a clear decrease in the membrane electrical resistance as a result of both polysulfone sulfonation and the increase of the concentration of modifying substances, although a kind of limit concentration was obtained for both polyethylene glycol and lignosulfonate (40 and 20%, respectively). Results also show a decrease of around 90% in electrical resistance due to polysulfone sulfonation, while the value of the dielectric constant (hydrated state) clearly increases.
Keywords: Sulfonated polysulfone membranes; Polyethylene glycol; Lignosulfate; Thermal treatment; Impedance spectroscopy; Equivalent circuits;

This paper investigates the effect of polyvinyl alcohol (PVA) as the intermediate layer of bipolar membranes on water dissociation. The bipolar membranes are prepared by coating a solution of sulfonated polyphenylene oxide (SPPO) on the anion exchange layers, which had been immersed in PVA aqueous solutions with different concentrations in advance. The experimental results show that the effect of PVA on water dissociation is significantly affected by its concentration: at low concentration range PVA solution catalyzes water dissociation and at high concentration range PVA solution shows a retardant effect. The phenomenon is different from the situation where polyethylene glycol (PEG) is used as the intermediate layer. Based on the adsorption data and the measurements of X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy, it is found that (1) the effect of PVA concentration on water dissociation can be explained by the competition and compromise of two effects—the catalytic and hydrophilic effect of the PVA molecule and the steric effect of the enlargement of junction thickness; (2) the reason that at high concentration range PVA and PEG show different effects on water dissociation is that the junction thickness is enlarged excessively by PVA, which is based on the intrinsic characteristics of PVA molecules.
Keywords: Bipolar membrane; Water dissociation; Polyvinyl alcohol; Polyethylene glycol;

Determination of kinetic parameters of Cu(II) interaction with chemically modified thin chitosan membranes by Antonio R. Cestari; Eunice F.S. Vieira; Joana D.S. Matos; Débora S.C. dos Anjos (288-295).
In this work, vanillin-modified thin chitosan membranes were utilized as adsorbents for the removal of Cu(II) from aqueous solutions. A rise of temperature accelerates mass transfer of Cu(II) to the membranes surfaces. The kinetic data did present a rough fit to the traditional Lagergren adsorption kinetic equations. An alternative Avrami kinetic equation was successfully fitted to the kinetic adsorption quantities. From this new equation, from one to three regions presenting distinct kinetic parameters were found, and the use of the parameter n was also related to the determination of the kinetic orders. Variations of the adsorption rate in relation to the contact time and the temperature were also calculated and are discussed.
Keywords: Chitosan membranes; Vanillin; Cu(II) adsorption; Adsorption kinetic modeling; Avrami adsorption model;

A theoretical model of the evaporation of a pure liquid layer is developed. We focus on the influence of an inert gaseous component, in addition to vapor, on surface-tension-driven Bénard instabilities. It is assumed that the gas phase is perfectly mixed at some distance from the liquid–gas interface (given composition, pressure, and temperature). If this distance is not much larger than the liquid layer thickness, it is shown that a reduction of the full two-layer problem to a one-layer problem is possible, provided the evaporation rate is not too large. An analytical expression is given for the corresponding dimensionless heat transfer coefficient (a generalized, wavenumber-dependent Biot number) at the evaporating interface. The approach is validated through a comparison with a direct numerical resolution of the full two-layer problem.
Keywords: Heat transfer; Mass transfer; Evaporation; Marangoni instability;

Vapor-grown graphite nanofibers (GNFs) were modified by plasma treatments using low-pressure plasmas with different gases (Ar gas only and/or Ar/O2 gases), flow rates, pressures, and powers. Surface characterizations and morphologies of the GNFs after plasma treatment were investigated by X-ray photoelectron spectroscopy (XPS), contact angle, titration, and transmission electron microscopy (TEM) measurements. Also, the investigation of thermomechanical behavior and impact strengths of the GNFs/epoxy composites was performed by dynamic–mechanical thermal analysis (DMTA) and Izod impact testing, respectively. The plasma treatment of the fibers changed the surface morphologies by forming a layer with a thickness on the order of 1 nm, mainly consisting of oxygen functional groups such as hydroxyl, carbonyl, and carboxyl groups. After functionalization of the complete surfaces, further plasma treatment did not enhance the superficial oxygen content but slightly changed the portions of the functional groups. Also, the composites with plasma-treated GNFs showed an increase in T g and impact strength compared to the composites containing the same amount of plasma-untreated GNFs.
Keywords: Vapor-grown graphite nanofibers; Atmospheric pressure plasma; Surface characteristics; Oxygen functional groups; Impact strength;

The surface energy of talc by Ahmed K. Helmy; E.A. Ferreiro; S.G. de Bussetti (314-317).
The determination of an average value for the surface energy of talc ( γ ¯ S ) via solid–water interfacial interactions is described. It is based on a formula obtained by the combination of the Young equation with a general equation of pair interaction. Important features of the method are (a) the use of the Young equation to determine the range where the value of the surface energy lies and (b) the determination of the mean value within this range using a probability function. The value found is 217.31   mJ m −2 in the range 193.36 – 257.43   mJ m −2 .
Keywords: Adsorption of water; Surface energy; Surface tension; Talc;

Investigation of the mobility of amphiphilic polymer—AOT reverse microemulsion systems using electron spin resonance by Thomas H. Wines; P. Somasundaran; Nicholas J. Turro; Steffen Jockusch; M. Francesca Ottaviani (318-325).
Amphiphilic polymers can be used as tools to manipulate the behavior of reverse microemulsions. EPR spectroscopy employing the spin probe 5-doxyl stearic acid was used to study the adsorption of a comb type polymer (polymaleic anhydride octyl vinyl ether) and a diblock polymer (polybutadiene–ethylene oxide) onto reverse microemulsion droplets formed from Aerosol-OT/heptane/water. The findings indicate that the comb type polymer was adsorbed by the reverse microemulsion drops at low polymer concentrations causing a structural change of the micelle.
Keywords: Microemulsion; Reverse; Nonaqueous; Polymer; Block; Comb; Electrical percolation; AOT;

Molecular interactions between paclitaxel, an anticancer drug, and phospholipids of various chain unsaturations and headgroup types were investigated in the present study by Langmuir film balance and differential scanning calorimetry. Both the lipid monolayer at the air–water interface and the lipid bilayer vesicles (liposomes) were employed as model cell membranes. It was found that, regardless of the difference in molecular structure of the lipid chains and headgroup, the drug can form nonideal, miscible systems with the lipids at the air–water interface over a wide range of paclitaxel mole fractions. The interaction between paclitaxel and phospholipid within the monolayer was dependent on the molecular area of the lipids at the interface and can be explained by intermolecular forces or geometric accommodation. Paclitaxel is more likely to form thermodynamically stable systems with 1,2-dipalmitoyl-sn-glycerol-3-phosphocholine (DPPC) and 1,2-dielaidoyl-sn-glycero-3-phosphocholine (DEPC) than with 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE) and 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC). Investigation of the drug penetration into the lipid monolayer showed that DPPC and DEPC have higher incorporation abilities for the drug than DPPE and DSPC. A similar trend was also evidenced by DSC investigation with liposomes. While little change of DSC profiles was observed for the DPPE/paclitaxel and DSPC/paclitaxel liposomes, paclitaxel caused noticeable changes in the thermographs of DPPC and DEPC liposomes. Paclitaxel was found to cause broadening of the main phase transition without significant change in the peak melting temperature of the DPPC bilayers, which demonstrates that paclitaxel was localized in the outer hydrophobic cooperative zone of the bilayer, i.e., in the region of the C1–C8 carbon atoms of the acyl chain or binding at the polar headgroup site of the lipids. However, it may penetrate into the deeper hydrophobic zone of the DEPC bilayers. These findings provide useful information for liposomal formulation of anticancer drugs as well as for understanding drug–cell membrane interactions.
Keywords: Anticancer drugs; Differential scanning calorimetry (DSC); Drug delivery; Langmuir trough; Lipid bilayers; Lipid monolayers; Liposomes;

The effect of additives on the water solubilization capacity and conductivity in n-pentanol microemulsions by Xiaoguang Zhang; Jinfeng Dong; Gaoyong Zhang; Xinlin Hong; Xuefeng Li (336-341).
The influence of additives such as sodium salicylate and sodium chloride on the water solubilization capacity of AOT in n-pentanol solutions has been investigated. The water solubilization capacity is enhanced by sodium salicylate and decreased by sodium chloride. The percolation behavior of the water/AOT/n-pentanol system is studied by modifying the water concentration and temperature. No percolation threshold induced by water or temperature is detected either in the absence or in the presence of additives. The values of ln σ have a linear correlation with temperature in the range of 5–40 °C. The activation energy is also estimated and discussed.
Keywords: Pentanol microemulsion; Water solubilization capacity; Conductivity; Additives; Percolation; AOT;

Interactions in mixed cationic surfactants and dextran sulfate aqueous solutions by V. Tomašić; A. Tomašić; I. Šmit; N. Filipović-Vinceković (342-350).
The interactions between a hydrophilic anionic polysaccharide, dextran sulfate, and oppositely charged surfactants, n-alkylammonium chlorides (the number of carbon atoms per chain being 10, 12, and 14), were investigated by optical microscopy, X-ray diffraction, microelectrophoretic mobility, conductivity, surface tension, and light-scattering measurements at 303 K. The increase of surfactant alkyl chain length shifts both the critical aggregation (cac) and the critical micelle concentrations (cmc) toward lower surfactant concentration. Light-scattering and microelectrophoretic data revealed the coexistence of differently structured complexes beyond the cac. The presence of giant vesicles indicates that at least one type of species is ordered in bilayers. X-ray analysis of dry n-alkylammonium dextran sulfates exhibited mesomorphous ordering and interplanar spacings typical for lamellar structures; i.e., n-alkylammonium molecules form more or less disordered bilayers interconnected with dextran sulfate chains, thus forming multilamellar stacks. The average basic lamellar thickness increased linearly with the increase of surfactant chain length, whereas the average number of lamellar bilayers in the stack of lamellae decreases.
Keywords: n-Alkylammonium chlorides; n-Alkylammonium dextran sulfates; Dextran sulfate; Giant vesicles; Lamellar structures;

Investigation of interaction parameters in mixed micelle using pulsed field gradient NMR spectroscopy by H. Gharibi; S. Javadian; B. Sohrabi; R. Behjatmanesh (351-359).
Pulsed field gradient NMR spectroscopy was used to determine the partitioning of surfactant between monomeric and micellar forms in a mixed CTAB (hexadecyltetramethylammonium bromide) and Triton X-100 [p-(1,1,3-tetramethylbutyl)polyoxyethylene] system. In addition, potentiometric and surface tension measurements were used to determine the free concentration of ionic surfactant and the critical micelle concentration (CMC) of mixtures of n-alkyltrimethylammonium bromide ( C n TAB, n = 12 , 14, 16, 18) and Triton X-100. Regular solution theory cannot describe the behavior of the activity coefficient and the excess Gibbs free energy of mixtures of ionic and nonionic surfactants. To overcome these shortcomings, we developed a new model that combines Van Laar expressions and the theory of nonrandom mixing in mixed micelles. The Van Laar expressions contain an additional parameter, ρ, which reflects differences in the size of the components of the mixture. Nonrandom mixing theory was introduced to describe nonrandom mixing in mixed micelles. This effect was modeled by a packing parameter, P ∗ . The proposed model provided a good description of the behavior of binary surfactant mixtures. The results indicated that head group size and packing constraints are important contributors to nonideal surfactant behavior. In addition, the results showed that as the chain length of the C n TAB molecule in C n TAB/Triton X-100 mixtures was increased, the head group size parameter remained constant, but the interaction and packing parameters increased. Increase of the temperature caused an increase in the interaction parameter β and a decrease in the packing parameter ( P ∗ ) .
Keywords: Surfactant; Mixed micelles; Triton X-100; Alkyltrimethylammonium bromide; Regular solution theory; Packing parameter; Head group size; PFG-NMR; Ion-selective electrode; Surface tension;

The morphology and stability of small unilamellar egg yolk phosphatidylcholine (EggPC) liposomes modified with the Pluronic® copolymer (poly (oxyethylene)–poly (oxypropylene)–poly (oxyethylene) (PEO–PPO–PEO)) with different compositions on mica surface have been investigated using atomic force microscopy. Morphology studies reveal significant morphological changes of liposomes upon incorporating the Pluronic® copolymer. Bilayers are observed for Pluronic® with small hydrophilic (PEO) chain lengths such as L81 [(PEO)2(PPO)40(PEO)2] and L121 [(PEO)4(PPO)60(PEO)4]; bilayer and vesicle coexistence is observed for P85 [(PEO)26(PPO)39.5(PEO)26] and F87 [(PEO)61.1(PPO)39.7(PEO)61.1]; and stable vesicles are observed for F88 [(PEO)103.5(PPO)39.2(PEO)103.5], F127 [(PEO)100(PPO)65(PEO)100], and F108 [(PEO)132.6(PPO)50.3(PEO)132.6]. The micromechanical properties of Pluronic®-modified EggPC vesicles were studied by analyzing AFM approaching force curve. The bending modulus ( k c ) of the Pluronic®-modified EggPC vesicles increased several-fold compared with that of the pure EggPC vesicles. The significant difference is due to the enhanced rigidity of the EggPC vesicles as a result of the incorporation of PPO molecules and PEO chains. Based on the analysis of onset point by AFM and diameters of vesicles by light scattering, it was concluded that the favorable model to describe the polymer–bilayer interaction is the membrane-spanning model.
Keywords: Small unilamellar vesicle; PEO–PPO–PEO copolymer; Stability; Morphology; Atomic force microscopy;

The phase behavior of the water/poly(oxyethylene)–poly(dimethylsiloxane) copolymer (Si25C3EO51.6)/pentaoxyethylene dodecyl ether (C12EO5) ternary system has been studied. Both the silicone copolymer and the surfactant have equal volumes of hydrophilic and lipophilic parts; i.e., these are balanced amphiphiles. Although only a lamellar phase is observed in water–Si25C3EO51.6 and water–C12EO5 binary systems, a variety of liquid crystalline phases, including normal micellar cubic (I1), hexagonal (H1), bicontinuous cubic (V1), lamellar (L α ), reverse bicontinuous cubic (V2), and reverse hexagonal (H2), are observed in the copolymer-rich region of the ternary phase diagram. The small C12EO5 molecules dissolve at the hydrophobic interface in the thick bilayer of the Si25C3EO51.6 L α phase occupying a large area of the total interface of the aggregates and modulate the curvature of the aggregates. Hence a variety of self-assembled structures are observed. In contrast, Si25C3EO51.6 is not dissolved in the thin bilayer of the C12EO5 lamellar phase (L α ). Hence, the C12EO5 L α phase coexists with copolymer-rich L α and H2 phases. Consequently, small surfactant molecules are dissolved in a large silicone copolymer aggregate to induce a change in layer curvature, but a large copolymer molecule is hard to incorporate with surfactant aggregates.
Keywords: Phase behavior; Self-assembly; Liquid crystal; Silicone copolymer; Nonionic surfactant;

Acid–base equilibrium of anionic dyes partially bound to micelles of nonionic surfactants by Palash M. Saikia; Munindra Bora; Robin K. Dutta (382-387).
The acid–base equilibria of the sulfonephthalein dyes, namely, bromothymol blue, thymol blue, and cresol red, in aqueous nonionic micellar solutions of Triton X-100, Tween-20, Tween-40, Tween-60, and Tween-80 have been investigated. The equilibrium constants of the partition of the dyes between micellar and aqueous pseudophases have been determined spectrophotometrically at fixed pH. The K ass increased with the surfactants in the order Tween-80 < Tween-60 < Tween-40 < Tween-20 < TX-100. The effect of such associations on the p K a 2 of the dyes at various concentrations of the nonionic surfactant has been studied. The p K a 2 of the dyes as a function of the concentrations of the surfactant was predicted from the equilibrium constants using a method developed to fit nonionic surfactants and was compared with experimental values determined directly. The p K a 2 s of the dyes predicted according to the present method have been found to be in good agreement with the experimental values.
Keywords: Sulfonephthalein dyes; Partition equilibrium; Nonionic surfactant; Acid–base equilibrium; Micelles;

The influence of surfactant mixing ratio on nano-emulsion formation by the pit method by Paqui Izquierdo; Jin Feng; Jordi Esquena; Tharward F. Tadros; Joseph C. Dederen; Maria José Garcia; Núria Azemar; Conxita Solans (388-394).
The formation of O/W nano-emulsions by the PIT emulsification method in water/mixed nonionic surfactant/oil systems has been studied. The hydrophilic–lipophilic properties of the surfactant were varied by mixing polyoxyethylene 4-lauryl ether ( C ¯ 12 E ¯ 4 ) and polyoxyethylene 6-lauryl ether ( C ¯ 12 E ¯ 6 ). Emulsification was performed in samples with constant oil concentration (20 wt%) by fast cooling from the corresponding HLB temperature to 25 °C. Nano-emulsions with droplet radius 60–70 nm and 25–30 nm were obtained at total surfactant concentrations of 4 and 8 wt%, respectively. Moreover, droplet size remained practically unchanged, independent of the surfactant mixing ratio, X C12E6 . At 4 wt% surfactant concentration, the polydispersity and instability of nano-emulsions increased with the increase in X C12E6 . However, at 8 wt% surfactant concentration, nano-emulsions with low polydispersity and high stability were obtained in a wide range of surfactant mixing ratios. Phase behavior studies showed that at 4 wt% surfactant concentration, three-liquid phases (W + D + O) coexist at the starting emulsification temperature. Furthermore, the excess oil phase with respect to the microemulsion D-phase increases with the increase in X C12E6 , which could explain the increase in instability. At 8 wt% surfactant concentration, a microemulsion D-phase is present when emulsification starts. The low droplet size and polydispersity and higher stability of these nano-emulsions have been attributed, in addition to the increase in the surface or interfacial activity, to the spontaneous emulsification produced in the microemulsion D-phase.
Keywords: Nano-emulsion; Mixed surfactant system; HLB temperature; Emulsion stability; Phase behavior; Ostwald ripening; Phase inversion temperature (PIT) method;

Micellar enhanced ultrafiltration (MEUF) of different phenolic derivatives including meta-nitrophenol (MNP), catechol (CC), para-nitrophenol (PNP), and beta-napthol (BN) in their binary mixture has been studied. A 1:1 ratio of the mixture of (i) MNP with CC and (ii) PNP with BN is taken for the MEUF experiments using a cationic surfactant, namely, cetyl(hexadecyl)pyridinium chloride (CPC). An organic polyamide membrane with molecular weight cutoff of 1000 is used. Experiments are conducted using an unstirred batch cell and a continuous cross-flow cell. The effects of various operating conditions, e.g., concentrations of surfactant and solute in the feed, transmembrane pressure drop, and cross-flow rate (for cross-flow experiments) on the permeate flux and the observed retention of each solute have been studied in detail. The retention of solutes without using the surfactant varies from 3 to 15% only at a typical feed solute concentration of 0.09 kg/m3, whereas, under the same operating pressure (345 kPa), retention at the end of the experiment increases to about 66 to 99.8% depending on the nature of solute in the batch cell using surfactant micelles (10 kg/m3). Retention of solutes is less in the case of the two-component feed solution compared to the single-component feed solution. An increase in flux to the range of 9 to 16% is realized in cross-flow experiments compared to batch cell flux after one hour of operation.
Keywords: Phenolic derivative; Cationic surfactant; Micellar enhanced ultrafiltration; Permeate flux; Observed retention; Transmembrane pressure drop;

Antagonistic mixing behavior of cationic gemini surfactants and triblock polymers in mixed micelles by Mandeep Singh Bakshi; Jasmeet Singh; Gurinder Kaur (403-412).
Conductance ( κ ) , pyrene fluorescence ( I 1 / I 3 ) , cloud point ( C P ) , and Krafft temperature ( K T ) measurements have been carried out for various dimethylene bis(alkyldimethylammonium bromide) (gemini) surfactants with different poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) triblock polymers (TBP). From the κ and I 1 / I 3 studies, the critical micelle concentrations of mixed micelle formation between the gemini and TBP have been determined using regular solution theory. It has been observed that mixed micelle formation in all the binary mixtures of gemini + TBP occurs due to the unfavorable mixing, the magnitude of which decreases with increased hydrophobicity of the gemini component. The results are further supported by evaluating the mean micelle aggregation number and enthalpy of fusion from fluorescence and Krafft temperature measurements, respectively.
Keywords: Cationic gemini surfactants; Triblock polymers; Mixed micelles; Fluorescence studies; Hydrophobicity;

Transport of liquids using superhydrophobic aerogels by A. Venkateswara Rao; Manish M. Kulkarni; Sharad D. Bhagat (413-418).
The experimental results of the studies on the transportation of water droplets on a superhydrophobic silica aerogel-powder-coated surface are reported. The superhydrophobic silica aerogels were prepared using sol–gel processing of methyltrimethoxysilane (MTMS) precursor, methanol (MeOH) solvent, and base (NH4OH)-catalyzed water followed by supercritical drying using methanol solvent. The molar ratio of NH4OH/MTMS, H2O/MTMS, and MeOH/MTMS were varied from 1.7 × 10 −1 to 3.5 × 10 −1 , 2 to 8, and 1.7 to 14, respectively, to find out the best-quality aerogels in terms of higher hydrophobicity and high droplet velocity. A specially built device was used for the measurement of velocity of water droplet of size 2.8 mm ( ± 0.2  mm ) on an inclined surface coated with superhydrophobic aerogel powder. Liquid marbles were prepared by rolling water droplets on aerogel powder and the marble(s) velocities on a noncoated inclined surface were compared with that of the water droplets. It was observed that the microstructure of the aerogel affects the droplet as well as marble velocities considerably. For an aerogel with uniform and smaller particles, the water droplet and marble velocities were observed to be maximum, i.e., 144 and 123 cm/s, respectively, whereas for the aerogels with bigger and nonuniform particles, the water droplet and marble velocities were observed to be minimum, i.e., 92 and 82 cm/s, respectively. The results have been discussed by taking into account the contact angles and microstructural observations.
Keywords: Aerogels; SEM; Surface treatments; Gels and sols; Velocity;

A comprehensive study of the AC and DC electrokinetic properties of submicrometre latex particles as a function of particle size and suspending medium conductivity and viscosity is presented. Electrophoretic mobility and dielectrophoretic cross-over results were measured for particle diameters ranging from 44 to 2000 nm. The zeta potentials of the particles were calculated from the electrophoretic mobility data for different suspending medium conductivities, using various models, with and without the inclusion of surface conduction. The dielectrophoretic data was analysed to derive values for the Stern layer conductance and zeta potentials.
Keywords: Latex spheres; Surface conductance; Stern layer; Diffuse layer; Nanoparticles; Electrokinetic properties;

The validity of the Vogel–Tammann–Fulcher type asymptotic exponential functions for representing the temperature dependence of various properties, such as the particle–particle pull-off adherence forces in ice and hydrates and the annealing effect on polystyrene latex films, is demonstrated. The parameters of this equation are determined using the reported experimental data. The applications show that such functions yield accurate correlations of the experimental property data measured at various temperatures.
Keywords: Temperature dependence; Vogel–Tammann–Fulcher equation; Asymptotic exponential functions; Particle–particle pull-off; Adherence force; Annealing; Ice; Hydrate; Polystyrene latex;

by Arthur Hubbard (433).