Journal of Colloid And Interface Science (v.286, #1)

Adsorption of n-heptyl xanthate on synthesized zinc sulfide was followed in situ by monitoring the methylene absorption band at 2925 cm−1. The zinc sulfide surface used in the adsorption experiments was synthesized on a germanium internal reflection element using the chemical bath deposition method. Characterization of the adsorbent surface was performed by X-ray photoelectron spectroscopy. The time needed to reach adsorption equilibrium varied with the initial concentration of the aqueous potassium heptyl xanthate solution. The amount of adsorbed xanthate ions increased with the concentration of the solution within the range studied (10 μM–50 mM). The experimental data are reasonably well described by the Langmuir adsorption isotherm. Polarized infrared attenuated total reflection (ATR) was used to determine the average orientation of the heptyl chains by measuring the absorbance of the infrared beam polarized perpendicularly and parallely to the plane of incidence. Measured absorbances were corrected for contribution from heptyl xanthate in bulk solution.
Keywords: IR-ATR; Chemical bath deposition; Zinc sulfide; Polarized IR-ATR; Heptyl xanthate;

An improved predictive correlation for the induction time of CaCO3 scale formation during flow in porous media by E. Stamatakis; A. Stubos; J. Palyvos; C. Chatzichristos; J. Muller (7-13).
The induction time, t ind , of calcium carbonate precipitation in porous rocks was experimentally measured under dynamic conditions at temperatures from 25 to 120 °C with the use of a radiotracer technique, where the gamma-emitting nuclide 47Ca was used as a tracer in order to monitor the scale deposition at real time. Based upon nucleation theory and experimental observations, the following improved correlation is proposed: log t ind ( min ) = 3.2 − 3.0 SI − 959.8 T + 1849.9 SI T . This equation predicts satisfactorily the induction time of calcium carbonate scale formation under specific dynamic (flow) conditions in the near-well region (T is the absolute temperature in K, and SI is the saturation index, SI = log SR , where SR is the saturation ratio).
Keywords: Induction time; Scale formation; Calcium carbonate; Porous media;

Modeling of adsorption dynamics at air–liquid interfaces using statistical rate theory (SRT) by M.E. Biswas; I. Chatzis; M.A. Ioannidis; P. Chen (14-27).
A large number of natural and technological processes involve mass transfer at interfaces. Interfacial properties, e.g., adsorption, play a key role in such applications as wetting, foaming, coating, and stabilizing of liquid films. The mechanistic understanding of surface adsorption often assumes molecular diffusion in the bulk liquid and subsequent adsorption at the interface. Diffusion is well described by Fick's law, while adsorption kinetics is less understood and is commonly described using Langmuir-type empirical equations. In this study, a general theoretical model for adsorption kinetics/dynamics at the air–liquid interface is developed; in particular, a new kinetic equation based on the statistical rate theory (SRT) is derived. Similar to many reported kinetic equations, the new kinetic equation also involves a number of parameters, but all these parameters are theoretically obtainable. In the present model, the adsorption dynamics is governed by three dimensionless numbers: ψ (ratio of adsorption thickness to diffusion length), λ (ratio of square of the adsorption thickness to the ratio of adsorption to desorption rate constant), and N k (ratio of the adsorption rate constant to the product of diffusion coefficient and bulk concentration). Numerical simulations for surface adsorption using the proposed model are carried out and verified. The difference in surface adsorption between the general and the diffusion controlled model is estimated and presented graphically as contours of deviation. Three different regions of adsorption dynamics are identified: diffusion controlled (deviation less than 10%), mixed diffusion and transfer controlled (deviation in the range of 10–90%), and transfer controlled (deviation more than 90%). These three different modes predominantly depend on the value of N k . The corresponding ranges of N k for the studied values of ψ ( 10 −2 < ψ < 10 4 ) and λ ( 10 −12 < λ < 10 8 ) are 10 1 < N k < 10 4 for the diffusion controlled, 10 −3 < N k < 10 1 for the mixed diffusion and transfer controlled, and 10 −4 < N k < 10 −3 for the transfer controlled, respectively. The study also shows that lower values of ψ and λ are favorable for maximum surface adsorption and consequently surface tension reduction.
Keywords: Adsorption dynamics; Statistical rate theory; Numerical solution; Method of lines; Diffusion controlled; Mixed diffusion and transfer controlled; Transfer controlled; Contour of deviation;

Adsorption of human insulin and AspB28 insulin on a PTFE-like surface by S.H. Mollmann; J.T. Bukrinsky; S. Frokjaer; U. Elofsson (28-35).
The interactions of human insulin, Zn-free human insulin, and AspB28 insulin with a hydrophobic surface were studied by ellipsometry. All three insulin types investigated adsorbed with high affinity onto the hydrophobic surface, as the plateau of the adsorption isotherm, represented by the irreversible bound fraction, was reached at concentrations > 10 −3 mg/ml. The plateau values for human insulin and Zn-free human insulin could not be distinguished with statistical significance, whereas the plateau value for AspB28 insulin was lower than those for the two others, with an adsorbed amount corresponding to a monolayer of insulin monomers. The results observed may be explained by differences in self-association patterns of the insulin types or by enhanced charge repulsion between the AspB28 analog and the negatively charged surface.
Keywords: Ellipsometry; Insulin; Protein adsorption; Insulin analog; PTFE; Teflon;

Adsorption mechanism of synthetic reactive dye wastewater by chitosan by Niramol Sakkayawong; Paitip Thiravetyan; Woranan Nakbanpote (36-42).
Chitosan was able to remove the color from synthetic reactive dye wastewater (SRDW) under acidic and caustic conditions. The effect of the initial pH on SRDW indicated that electrostatic interaction occurred between the effective functional groups (amino groups) and the dye under acidic conditions. Moreover, SRDW adsorption under caustic conditions was also affected by the covalent bonding of dye and hydroxyl groups of chitosan. In addition, elution tests confirmed that chemical adsorption occurred under acidic conditions, while both physical and chemical adsorption appeared under caustic conditions. The spectra of attenuated total reflectance Fourier transform infrared spectrometry confirmed the functional groups of chitosan that affected the SRDW adsorption. However, the maximum adsorption capacities of chitosan increased when the temperature increased. The maximum adsorption capacity of chitosan obtained from the Langmuir model was 68, 110, and 156 mg g−1 under a system pH of 11.0 at 20, 40, and 60 °C, respectively. The negative values of enthalpy change (ΔH), free energy change (ΔG), and entropy change (ΔS) indicated an exothermic, spontaneous process and decreasing disorder of the system, respectively. Therefore, the mechanism of SRDW adsorption by chitosan was probably by chemical adsorption for a wide range of pH's and at high temperatures.
Keywords: Adsorption; ATR-FTIR; Chitosan; Reactive dye wastewater; Electrostatic; Thermodynamic;

Removal of Pb2+ and Ni2+ from aqueous solutions by sorption onto natural bentonite was investigated. Experiments were carried out as a function of particle size, the amount of bentonite, pH, concentration of metals, contact time, and temperature. The adsorption patterns of metal ions onto followed the Langmuir, Freundlich, and Dubinin–Radushkevich isotherms. This included adsorption isotherms of single-metal solutions at 303 K by batch experiments. The thermodynamic parameters ( Δ H , Δ S , Δ G ) for Pb2+ and Ni2+ sorption onto bentonite were also determined from the temperature dependence. The adsorptions were endothermic reactions. The results suggested that natural bentonite is suitable as a sorbent material for recovery and adsorption of metal ions from aqueous solutions.
Keywords: Natural bentonite; Pb2+ and Ni2+; Sorption isotherm;

Adsorption and kinetic studies of cationic and anionic dyes on pyrophyllite from aqueous solutions by Aslıhan Gücek; Savaş Şener; Sedat Bilgen; M. Ali Mazmancı (53-60).
The adsorption of cationic Methylene Blue (MB) and anionic Procion Crimson H-EXL (PC) dyes from aqueous medium on pyrophyllite was studied. Changes in the electrokinetics of pyrophyllite as a function of pH were investigated in the absence and presence of multivalent cations. The results show that pyrophyllite in water exhibits a negative surface charge within the range pH 2–12. Pyrophyllite is found to be a novel adsorbent for versatile removal of cationic and anionic dyes. The negative hydrophilic surface sites of pyrophyllite are responsible for the adsorption of cationic MB molecules. The adsorption of anionic PC dye is possible after a charge reversal by the addition of trivalent cation of Al. Nearly 2 min of contact time are found to be sufficient for the adsorption of both dyes to reach equilibrium. The experimental data follow a Langmuir isotherm with adsorption capacities of 70.42 and 71.43 mg dye per gram of pyrophyllite for MB and PC, respectively. For the adsorption of both MB and PC dyes, the pseudo-second-order chemical reaction kinetics provides the best correlation of the experimental data.
Keywords: Pyrophyllite; Zeta potential; Dye; Adsorption isotherm; Adsorption kinetics;

Electrolyte and pH effects on Pb(II)–calcite sorption processes: the role of the PbCO0 3(aq) complex by Ashaki A. Rouff; Richard J. Reeder; Nicholas S. Fisher (61-67).
Batch sorption experiments were conducted under conditions of ambient temperature and atmospheric PCO2(g) to determine the effects of electrolyte type, ionic strength, and pH on Pb(II) interactions with calcite. For 0.15 M nitrate and chloride solutions at pH 8.2, no significant effect of electrolyte type on Pb sorption was observed. Varying ionic strength from 0.15 to 0.5 M produced little effect on Pb sorption in nitrate compared to chloride solutions in which Pb uptake decreased with increasing ionic strength. For a pH range of 7.3–9.4 in 0.15–0.2 M nitrate solutions, Pb sorption increased from pH 7.3 to 8.5 with a subsequent decrease in uptake out to pH 9.4. The trends in electrolyte and pH experiments correlate well with those for PbCO0 3(aq) speciation, indicating that this metal–ligand complex in solution dictates Pb sorption in the system under investigation.
Keywords: Lead(II); Calcite; CaCO3; Adsorption; Lead carbonate; Surface complexation;

Passivation of the calcite surface with phenylmalonate and benzylmalonate ions by Manlio F. Salinas-Nolasco; Juan Méndez-Vivar; Víctor H. Lara; Pedro Bosch (68-81).
We explored the affinity of calcite to adsorbed organic molecules as an approach to the conservation of cultural heritage built of marble and limestone. The utilization of phenylmalonic and benzylmalonic acids provided a hydrophobic adsorptive interface, adequate to prevent processes of aqueous weathering. Samples of marble powder (polycrystalline calcite) were impregnated with solutions of phenylmalonic and benzylmalonic acid at three concentrations ( 5 × 10 −2 , 5 × 10 −3 , and 5 × 10 −4  M ) and different pH values (6.00, 7.00, and 8.00). The surface charge of the calcite suspensions was determined by potentiometric measurements under equilibrium conditions at room temperature in aqueous solution of the dicarboxylic acids, in order to understand the influence of the electrokinetic potential in the surface association. The adsorbed amounts were determined by calculation of the thermodynamic equilibria of solutions. The presence of the organic interface on the mineral surface was corroborated by Raman spectroscopy and small-angle X-ray scattering (SAXS). The results indicate effective adsorption of both dicarboxylic acids as a function of the concentration and pH, and several other conditions that favors coulombic interaction, an absence of electrophoretic mobility or surface electroneutrality related to the solid surface potentials. The coverage of pores by dicarboxylic adsorbate modified the geometrical pore shape and the pore size distribution, filling all the pores of larger than 80 Å diameter, giving as a result a mesoporous structure. This change in the surface morphology by organic adsorbates constitutes a modification in the diffusional processes of the environment on the mineral surface.
Keywords: Calcium carbonate; Calcite; Benzylmalonate ion; Phenylmalonate ion; Passivation; Surface charge; Raman spectroscopy; SAXS;

The sorption species and coordination environment of zinc sorbed on to hydrous ferric oxide (HFO) did not change for aging times up to six months. At an initial concentration of 10 4 − M, Zn formed innersphere surface complexes on the surface of HFO. Zn was tetrahedrally coordinated with oxygen atoms at Zn―O bond distance of ∼1.94–1.97 Å with coordination number of ∼3.8–4.7. In the second shell Zn appeared to be coordinated with Fe with a bond distance of ∼3.42–3.49 Å. At an initial concentration of 10 3 −   M , both innersphere and polynuclear complexes were feasible sorption products. The first shell was tetrahedrally coordinated with about four oxygen atoms at a bond distance of 1.96 Å. The second shell could be attributed to either Zn―Fe or Zn―Zn correlations with almost the same bond distance of 3.42–3.44 Å.
Keywords: Zn; Sorption; HFO; EXAFS;

Batch experiments were carried out for the sorption of methylene blue onto rice husk particles. The operating variables studied were initial solution pH, initial dye concentration, adsorbent concentration, and contact time. Equilibrium data were fitted to the Freundlich and Langmuir isotherm equations and the equilibrium data were found to be well represented by the Langmuir isotherm equation. The monolayer sorption capacity of rice husks for methylene blue sorption was found to be 40.5833 mg/g at room temperature (32 °C). The sorption was analyzed using pseudo-first-order and pseudo-second-order kinetic models and the sorption kinetics was found to follow a pseudo-second-order kinetic model. Also the applicability of pseudo second order in modeling the kinetic data was also discussed. The sorption process was found to be controlled by both surface and pore diffusion with surface diffusion at the earlier stages followed by pore diffusion at the later stages. The average external mass transfer coefficient and intraparticle diffusion coefficient was found to be 0.01133 min−1 and 0.695358 mg/g min0.5. Analysis of sorption data using a Boyd plot confirms that external mass transfer is the rate limiting step in the sorption process. The effective diffusion coefficient, D i was calculated using the Boyd constant and was found to be 5.05 × 10 −04   cm 2 / s for an initial dye concentration of 50 mg/L. A single-stage batch-adsorber design of the adsorption of methylene blue onto rice husk has been studied based on the Langmuir isotherm equation.
Keywords: Sorption; Rice husk; Methylene blue; Kinetics; Equilibrium; Mechanism; Process design;

Kinetic modeling of the adsorption of basic dyes by kudzu by Stephen J. Allen; Quan Gan; Ronan Matthews; Pauline A. Johnson (101-109).
The use of kudzu, a rapidly growing, high-climbing perennial leguminous vine, for the adsorption of basic dyes from aqueous solution has been investigated at various initial dye concentrations, masses of kudzu, and agitation rates. The extent and rate of adsorption of the three basic dyes (Basic Red 22, Basic Yellow 21, and Basic Blue 3) were analyzed using a pseudo-first-order and a pseudo-second-order kinetic model. While both rate mechanisms provided an acceptable degree of correlation with the experimental sorption rate data, the pseudo-second-order model gave a much higher degree of correlation, suggesting that this model could be used in design and simulation applications.
Keywords: Adsorption; Kudzu; Dye; Kinetics; First order; Second order;

Bacterial surface adsorption reactions are influenced by electric field effects caused by changes in ionic strength; however, existing datasets are too sparse to definitively constrain these differences or to determine the best way to account for them using thermodynamic models. In this study, we examine the ionic strength dependence of proton and metal adsorption onto the surfaces of Pseudomonas mendocina and Pseudomonas putida by conducting proton, Cd(II), Pb(II), and Sr(II) adsorption experiments over the ionic strength range of 0.001 to 0.6 M. Chosen experimental results are thermodynamically modeled using a non-electrostatic approach, a diffuse layer model (DLM), and a triple-layer model (TLM). The results demonstrate that bacterial surface electric field effects are negligible for proton, Cd, and Pb adsorption onto P. putida and P. mendocina, and that the discrete site non-electrostatic model developed in this study is adequate for describing these reactions. The extent of Sr adsorption is influenced by changes in the bacterial surface electric field; however, the non-electrostatic model better describes Sr adsorption behavior than the DLM or TLM. The DLM and TLM greatly overpredict the effect of the electric field for all adsorption reactions at all ionic strengths tested.
Keywords: Bacteria; Adsorption; Diffuse layer; Triple layer; Electrostatic; Cd; Sr; Pb;

The influences of solid-phase organic constituents on the partition of aliphatic and aromatic organic contaminants by Hui-Chen Huang; Jiunn-Fwu Lee; Huan-Ping Chao; Pei-Wen Yeh; Yi-Fan Yang; Wan-Li Liao (127-133).
The influence of natural organic matter (NOM) constituents on contaminant distribution coefficients was evaluated by determining the K oc values of aromatic and aliphatic organic compounds (solutes) with clays modified with both aromatic- and aliphatic-rich organic constituents. The studied compounds consisted of naphthalene, phenanthrene, n-pentane, and 2,3,4-trimethylmethane; the solid samples comprised two clays with little organic content, kaolinite and Ca-montmorillonite. Two aliphatic surfactants and three aromatic dyes, sorbed to the clays, served as reference NOM constituents. For solutes of comparable water solubilities, the organic-carbon normalized distribution coefficients ( K oc ) of the aliphatic solutes between sorbed aliphatic organic matter and aqueous solution slightly exceed those of the aromatic solutes. By contrast, the aromatic solutes exhibited higher K oc values than did the aliphatic compounds with sorbed aromatic-rich organic matter. The difference in K oc values could be attributed to either comparable solubility parameters or the difference in the chemical structure between nonionic organic solutes and specific components of the simulated NOM. The much higher K oc values observed for the aromatic solutes indicate that the NOM composition is a major factor determining the NOC environmental distribution.
Keywords: K oc ; Organic contaminant; NOM constituent; Solubility parameter; Dye; Surfactant;

Selective crystallization of calcium salts by poly(acrylate)-grafted chitosan by Andrónico Neira-Carrillo; Mehrdad Yazdani-Pedram; Jaime Retuert; Mario Diaz-Dosque; Sebastien Gallois; José L. Arias (134-141).
The biopolymer chitosan was chemically modified by grafting polyacrylamide or polyacrylic acid in a homogeneous aqueous phase using potassium persulfate (KPS) as redox initiator system in the presence of N , N -methylene-bis-acrylamide as a crosslinking agent. The influence of the grafted chitosan on calcium salts crystallization in vitro was studied using the sitting-drop method. By using polyacrylamide grafted chitosan as substrate, rosette-like CaSO4 crystals were observed. This was originated by the presence of sulfate coming from the initiator KPS. By comparing crystallization on pure chitosan and on grafted chitosan, a dramatic influence of the grafted polymer on the crystalline habit of both salts was observed. Substrates prepared by combining sulfate with chitosan or sulfate with polyacrylamide did not produce similar CaSO4 morphologies. Moreover, small spheres or donut-shaped CaCO3 crystals on polyacrylic acid grafted chitosan were generated. The particular morphology of CaCO3 crystals depends also on other synthetic parameters such as the molecular weight of the chitosan sample and the KPS concentration.
Keywords: Chitosan; Crystallization; Calcium carbonate; Calcium sulfate; Polymorphs;

The viscoelastic behavior of aqueous solutions of an ionic complex formed from poly(sodium 2-(acrylamido)-2-methylpropanesulfonate) and rodlike mixed micelles of dimethyloleylamine oxide (DMOAO) and hexadecyltrimethylammonium chloride (CTAC) was investigated under oscillatory conditions. The DMOAO/CTAC mixed micelles exhibited high zero-shear viscosities ( η 0 ) depending on the mole fraction of CTAC in the mixed micelle (Y) in the range 0 ⩽ Y ⩽ 0.25 . The addition of the polyanion had no effect on the rheological behavior of the mixed micelles when Y < 0.02 at an ionic strength (μ) of 0.2. However, when Y was increased to a certain level ( Y c ), η 0 decreased drastically; Y c depended on μ but not on the polymer concentration. These observations indicate the formation of an ionic complex between the polymer and micelle when Y ⩾ Y c . The reciprocal of steady-state compliance ( J e −1 ) began to decrease gradually at Y ≈ Y c and then leveled off at Y > 0.06 . The relaxation time ( τ ) was found to be more strongly dependent on Y. Thus, the large decrease in η 0 was attributed mainly to a decrease in τ while the number density of junctions decreased only slightly. Therefore, it is concluded that polymer–micelle complex maintains a rodlike structure with some entanglements remaining at Y < 0.12 .
Keywords: Rheological behavior; Interaction; Complex formation; Polyelectrolytes; Rodlike micelles; Poly(sodium 2-(acrylamido)-2-methylpropanesulfonate); Dimethyloleylamine oxide; Hexadecyltrimethylammonium chloride;

The phase behavior and some physicochemical properties of homopolymers (HP) and hydrophobically modified (HMP) polymers, as well as of polyelectrolytes (PE) and proteins (PR), in the presence of aqueous surfactants, or their mixtures, are discussed. Mixing the above components gives rise to the formation of organized phases, whose properties are controlled by polymer and/or surfactant content, temperature, pH, and ionic strength. Depending on the nature, concentration, and net charge of both solutes, molecular solutions, polymer–surfactant complexes, adsorption onto micelles and vesicles, gels, liquid crystalline phases, and precipitates are observed. Such rich polymorphic behavior is the result of a complex balance between electrostatic, excluded volume, van der Waals, and other contributions to overall system stability. It is also modulated by the molecular details and architecture of both the polymer and the surfactant. Different experimental methods allow investigation of the above systems and getting information on the nature of polymer–surfactant interactions (PSI). Surface adsorption and thermodynamic methods, together with investigation of the phase diagrams, give information on the forces controlling PSI and on the existence of different phases. Conductivity, QELS and viscosity allow estimating the size and shape of polymer–surfactant (protein–surfactant) complexes. Optical microscopy, cryo-TEM, AFM, NMR, fluorescence, and relaxation methods give more information on the above systems. Use of the above mixtures in controlling gelation, surface covering, preparing dielectric layers, and drug release is suggested.
Keywords: Polymers; Surfactants; Proteins; Hydrophobically modified polymers; Polyelectrolytes; Interactions; Thermodynamic and transport properties; Relaxation; Spectroscopic and structural characterization;

Organic–aqueous liquid (phenol) extraction is one of many standard techniques to efficiently purify DNA directly from cells. The cell components naturally distribute themselves into the two fluid phases in order to minimize interaction energies of the biological components with the surrounding solvents. The membrane components and protein partition to the interface between the organic and aqueous phases while the DNA stays in the aqueous phase. The aqueous phase is then removed with a purified DNA sample. This work studies the first steps towards miniaturizing this liquid extraction technique in a microfluidic device. The first step is to understand how the two liquid phases behave in microchannels. Due to the interfacial tension between the two liquid phases, novel approaches must be examined in order to obtain interfacial stability under flow conditions. The stability of the organic–aqueous interface is improved by reducing the interfacial tension between the two phases by incorporating a surfactant into the aqueous phase. The variation of the interfacial tension as a function of surfactant concentration is also quantified in this work. This has led to the ability to create stable stratified microflows in both a dual inlet and three inlet microfluidic systems. Also, the first step in understanding biological interactions at the organic–aqueous interface is investigated using a fluorescently labeled bovine serum albumin protein.
Keywords: Two-phase flow; Phenol extraction; Liquid extraction; DNA purification;

The interaction between DNA and cationic lipid films at the air–water interface by Marité Cárdenas; Tommy Nylander; Bengt Jönsson; Björn Lindman (166-175).
The interaction between DNA and positively charged dioctadecyldimethylammonium bromide (DODAB) and DODAB/disteroylphosphatidylcholine (DSPC) monolayers at the air–aqueous interface was studied by a combination of the surface film balance and Brewster angle microscopy. In presence of DNA, the ΠA isotherm of the cationic monolayer shifts to larger mean molecular areas due to the electrostatic interaction with DNA while the typical liquid expanded–liquid condensed phase transition for DODAB monolayers disappear and the monolayer remains to be in the liquid expanded phase. Furthermore, the morphology of the film dramatically changes, where the large dendritic-like condensed aggregates observed for DODAB monolayers vanish. The charge density of the monolayer was varied by using mixed monolayers with the zwitterionic DSPC and no large effect was observed on the interaction with DNA. By modeling the electrostatic interactions with the linearized Poisson–Boltzmann equation using the finite-element method and taking into account the assumption in the dielectric constants of the system, it was possible to corroborate the expansion of the cationic monolayer upon interaction with DNA as well as the fact that DNA does not seem to penetrate into the monolayer.
Keywords: Polyelectrolytes; DNA; Lipid; BAM; Films; Interfaces;

Sedimentation in bidisperse and polydisperse colloids by Andrew D. Watson; Gary C. Barker; Margaret M. Robins (176-186).
We introduce a simple force and flux balance model for sedimentation and creaming in high volume fraction, polydisperse colloidal suspensions. The model is set alongside monodisperse and bidisperse sedimentation data for latex spheres, and we suggest that the broadening of the larger species sedimentation profile observed in the bidisperse case is linked to the particle pressure gradient arising from the smaller species. The model gives a satisfactory qualitative description of real emulsion creaming data, but implies either that the effective droplet radius is larger than the measured droplet radius, or that the effective background viscosity is reduced. Increasing the particle pressure gradient results in interface broadening at short times. We propose that the smallest emulsion droplets contribute to this broadening.
Keywords: Sedimentation; Creaming; Polydisperse; Bidisperse; Burgers' equation; Emulsion; Concentrated colloid;

Magnetite nanoparticles with tunable gold or silver shell by Madhuri Mandal; Subrata Kundu; Sujit Kumar Ghosh; Sudipa Panigrahi; Tapan K. Sau; S.M. Yusuf; Tarasankar Pal (187-194).
Fe3O4 nanoparticles with size ∼ 13   nm have been prepared successfully in aqueous micellar medium at ∼ 80 °C . To make Fe3O4 nanoparticles resistant to surface poisoning a new route is developed for coating Fe3O4 nanoparticles with noble metals such as gold or silver as shell. The shell thickness of the core–shell particles becomes tunable through the adjustment of the ratio of the constituents. Thus, the route yields well-defined core–shell structures of size from 18 to 30 nm with varying proportion of Fe3O4 to the noble metal precursor salts. These magnetic nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), FTIR, differential scanning calorimetry (DSC), Raman and temperature-dependent magnetic studies.
Keywords: Magnetite nanoparticles; Tunable gold and silver shell; Glucose; Micelles;

A new multi-Monte Carlo (MMC) method is promoted to consider general dynamic equation (GDE) for particle coagulation and condensation/evaporation. MMC method introduces the concept of a “weighted fictitious particle” and is based on time-driven Monte Carlo technique, constant number of fictitious particles technique, and constant volume technique. MMC method for independent coagulation, for independent condensation/evaporation, and for simultaneous coagulation and condensation/evaporation are validated by some special cases in which analytical solutions exist, in which numerical results agree with corresponding analytical solutions well. Furthermore, the computation cost of MMC method is low enough to be applied in engineering computation and general scientific quantitative analysis.
Keywords: Monte Carlo method; Coagulation; Condensation/evaporation; General dynamic equation; Particle;

Dispersion of TiN in aqueous media by Jingxian Zhang; Liping Duan; Dongliang Jiang; Qingling Lin; Mikio Iwasa (209-215).
The dispersion of TiN powders in aqueous media was studied through XPS, zeta potential, adsorption, sedimentation, and rheology measurements. XPS showed that there are TiO2, TiN, and TiO x N y sites on the TiN particle surface. In the absence of dispersant, the isoelectric point (pHIEP) of the TiN particles was at pH 2.2. Based on the surface properties of TiN particles, a cationic polymer, polyethylene imine (PEI), was selected as a dispersant. In the presence of PEI, the pHIEP shifted from pH 2.2 to pH 11.10. It was evidenced that TiN slurries could be stabilized around pH 9.50 with 1–2 wt% PEI as dispersant. Subsequently, TiN slurries with solid content as high as 57 vol% were developed and exhibited dilatant rheological behavior at high shear rate. The results showed that PEI is an effective dispersant for TiN in aqueous media.
Keywords: Dispersant; Polyethylene imine; Adsorption; Stability;

Dispersions of single-walled carbon nanotubes in various solvents and aqueous surfactant emulsions were investigated to correlate the degree of dispersion state with Hansen solubility parameters ( δ t 2 = δ d 2 + δ p 2 + δ h 2 ). It was found that the nanotubes were dispersed or suspended very well in the solvents with certain dispersive component ( δ d ) values. They were precipitated in the solvents with high polar component ( δ p ) values or hydrogen-bonding component ( δ h ) values. The solvents in the dispersed group occupied a certain region in a 3-dimensional space of three components. The surfactants with a lipophilic group equal to and longer than decyl, containing 9 methylene groups and 1 methyl group, contributed to the dispersion of nanotubes in water. The surfactants in the dispersed group had a lower limit in the dispersive component ( δ d ) of the Hansen parameter.
Keywords: Single-walled carbon nanotubes; Dispersion; Solubility parameter;

Aging mechanisms of perfluorocarbon emulsions using image analysis by Mara G. Freire; Ana M.A. Dias; Maria A.Z. Coelho; João A.P. Coutinho; Isabel M. Marrucho (224-232).
The aging mechanisms of perfluorocarbon emulsions were investigated using image analysis. Oil-in-water emulsions of two perfluorocarbons, n-perfluorohexane and perfluorodecalin, were prepared with three emulsifiers, Lecithin, Span 20, and Pluronic F-68. The effect of the temperature and the replacement of water by an aqueous phase consisting of a microbial culture medium were also studied. The emulsions were prepared by sonication and their stability was followed through analysis of the evolution of mean droplet size. The results indicate that the stability of perfluorocarbon in water emulsions depends on all the parameters investigated and that two aging mechanisms, coalescence and molecular diffusion, may take place. Analysis of the evolution of the mean droplet size during long time periods indicate that coalescence is more common than previously reported for these systems and seems to be favored by a temperature increase.
Keywords: n-Perfluorohexane; Perfluorodecalin; Emulsions; Emulsion stability; Image analysis; Molecular diffusion; Ostwald ripening; Coalescence;

Preparation and characterization of polymer composite multilayers on SiO2 by Heather Trotter; Abbas A. Zaman; Richard Partch (233-238).
Poly(diallyldimethylammonium chloride) (PDADMAC) and poly(sodium 4-styrenesulfonate) (PSS) have been consecutively adsorbed onto 1.5-μm charged silica (SiO2) particles. Time-dependent adsorption studies indicate that, due to the strong ionic charge of the dissociated polycation in water, adsorption is complete in less than 30 min. Indications of the maximum adsorption density, changes in surface charge, and stability of the layered particles are demonstrated through adsorption isotherms and electrophoretic mobility (EPM) measurements. Further stability of the PDADMAC layer is demonstrated through multiwashing with ultra pure deionized water. Preliminary desorption studies of the PSS layer also illustrate a stabilized two-layer system. Due to the nature of the electrostatic charges on the surface of the SiO2 core particles and both polyelectrolytes in aqueous media, the use of polyelectrolytes as layering elements serves as a model for the assembly of time-released drug delivery particle systems.
Keywords: Multilayers; Polyelectrolytes; Self-assembling; Adsorption; Desorption;

Characterization of organic phases in the interlayer of montmorillonite using FTIR and 13C NMR by Jianxi Zhu; Hongping He; Lizhong Zhu; Xiaoyan Wen; Feng Deng (239-244).
The molecular conformation and mobility of the intercalated surfactant molecules cetyltrimethylammonium bromide (CTMAB) have been studied using Fourier transform infrared spectroscopy (FTIR) and high-resolution single-pulse 13C magic angle spinning nuclear magnetic resonance (13C SP MAS NMR) spectroscopy. The conformation and mobility of alkyl chains were found to be a function of the surfactant concentration. The splitting of the methylene scissoring mode at 1473–1463 cm−1 and the rocking mode at 730–720 cm−1 in FTIR are considered to be diagnostic of the packing density increase of the intercalated surfactants within the clay gallery. Compared with the 13C SP MAS NMR spectrum of CTMAB in the bulk state, 1–3 ppm upfield chemical shifts for end-methyl (δC16) and methylene (δC15, δC2–14) of the intercalated surfactant molecules in the hybrids indicate a freer conformational situation. For these hybrids, the conformational freedom decreases with increased of surfactant concentration. In addition, on ∼2 ppm downfield shift for the C1 carbon atom in the hybrids with higher surfactant content suggests a special local environment. This study demonstrates the different mobility of carbon atoms in the intercalated alkyl chain.
Keywords: Montmorillonite; Alkylammonium; Organic phase; FTIR; NMR;

Distribution of amines in water/AOT/n-hexane reverse micelles: influence of the amine chemical structure by Lilian Zingaretti; N. Mariano Correa; Liliana Boscatto; Stella M. Chiacchiera; Edgardo N. Durantini; Sonia G. Bertolotti; Claudia R. Rivarola; Juana J. Silber (245-252).
The distribution of different aliphatic and aromatic amines: n-butylamine (n-BA), isobutylamine (i-BA), tert-butylamine (t-BA), piperidine (PIP), N,N-dimethylaniline (DMA) and N-methylaniline (MA) in water/sodium 1,4-bis(2-ethylhexyl)sulfosuccinate(AOT)/n-hexane reverse micelles was investigated by steady-state fluorescence measurements. The partition constants were measured by an indirect method based on the effect that amine partitioning exert on the bimolecular rate of the reaction between a microphase incorporated fluorophore (Ru(bpy)2+ 3) and the quencher, (Fe(CN)3− 6). For MA, that can act as a quencher of the fluorophore a direct method was used. The results show that primary amines have larger partition constants than the secondary ones. For tertiary amines the distribution constants were practically negligible. Laser flash photolysis experiments confirmed that tertiary amines, both aliphatic and aromatic, are not incorporated to the micellar pseudophase. The effect of the amine structure on the partition constant was analyzed through linear solvation free energy relationships (LSER) using solute parameters and compared with those obtained for alcohols. Hydrogen bond interactions with the AOT polar heads appear to be the main driving force for the distribution of amines between the organic and micellar pseudophases, whereas the size of the alkyl or aromatic group tends to hinder it.
Keywords: Partition constant; AOT; Reverse micelles; Aliphatic amines; Aromatic amines; Alcohols; Fluorescence; LSER; Ru ( bpy ) 3 2 + ; Hydrogen bonding;

Literature data for gold dissolution in ammoniacal copper(II) thiosulfate solutions is reinterpreted on the basis of adsorption and mixed potential theory. The dissolution reaction appears to take place via the adsorption of copper(II)–ammonia–thiosulfate onto the gold surface, forming the adsorbed species ⊢Au(S2O3) n Cu(NH3)−(2n−2) p . Equilibrium constants for the formation of these species from Cu(NH3)2+ m are in the range K ads = 172 – 510 (molar units) for m = 4 , n = 1 or 2, and p = 2 or 3. These complexes decompose with a rate constant of k Au = 1.7 × 10 −4 mol m −2 s −1 , to produce Au(S2O3)3− 2 and Cu(NH3)+ 3 or Cu(NH3)+ 2, where the copper(I) complexes in solution are re-equilibrated to the more stable species Cu(S2O3)3− 2 and Cu(S2O3)5− 3.
Keywords: Gold oxidation kinetics; Ammoniacal copper(II); Thiosulfate; Surface reaction mechanism; Adsorption;

Calorimetric study of the reactions of n-alkylphosphonic acids with metal oxide surfaces by Jaime M. Ferreira; Stephen Marcinko; Richard Sheardy; Alexander Y. Fadeev (258-262).
The reaction enthalpies for the solution-phase self-assembly of n-alkylphosphonic acids on the surfaces of TiO2 and ZrO2 have been determined using isothermal titration calorimetry at 298 K. The reaction enthalpies were negative (exothermic) for methyl- and n-octylphosphonic acids and positive (endothermic) for n-octadecylphosphonic acid with both metal oxides. The enthalpy/energy analysis showed that the net enthalpy of the formation of self-assembled monolayers (SAMs) at solid–liquid interface can be presented as follows: Δ H r = − D − ( Δ H sol + Δ H dil ) − ( E S − E SAM ) , where D is the binding energy of the SAM molecules with the solid; Δ H sol and Δ H dil are the enthalpies of dissolution and dilution; E S and E SAM are the surface energies of bare solid and SAM, respectively. This equation predicted an increase (and the sign change) of the reaction enthalpy as the alkyl group in n-alkylphosphonic acid increased, which explained the experimental data. Using this equation, the binding energy ( D ) in the SAMs of n-octyl- and n-octadecylphosphonic acids were estimated: 55 ± 5   kJ / mol (for ZrO2) and 58 ± 7   kJ / mol (for TiO2).
Keywords: Self-assembled monolayers; Alkylphosphonic acid; Titania; Zirconia; Titration calorimetry;

Cathode material LiMn2−y Co y O4 spinels were prepared by annealing the mixed precursors, which were synthesized by a low heating solid state coordination method using lithium acetate, manganese acetate, cobalt acetate, and oxalic acid as original materials. The structures and morphologies of the LiMn2−y Co y O4 spinels were investigated as a function of annealing temperature and time. The results showed that all samples in different annealing temperature and time had the same spinel structure. There were some growth and agglomeration in the particles when annealing temperature increased from 450 to 650 °C. And the crystal structure was more perfect at the upper temperature. In addition, the electrochemical properties of LiMn2−y Co y O4 spinels used as cathode material for lithium-ion batterries were studied in detail in this paper.
Keywords: LiMn2−y Co y O4 spinels; Low heating solid state coordination method; Lithium-ion battery;

Beta zeolite colloidal nanocrystals supported on mesoporous MCM-41 by V. Mavrodinova; M. Popova; V. Valchev; R. Nickolov; Ch. Minchev (268-273).
Zeolite-based composite materials prepared by the embedding of the beta zeolite nanophase from aqueous colloidal solution into matrices of preformed Si(Al)MCM-41 mesoporous molecular sieves have been characterized by different methods (XRD, SEM, FTIR, N2 adsorption, and TPD of NH3). Their potential as catalysts for toluene disproportionation has been compared to mechanical mixtures of freeze-dried nanobeta crystallites with Si(Al)MCM-41 mesoporous materials. It is found that the zeolite catalyst efficiency is not substantially changed by the presence of mesopores belonging to the matrix. It is suggested that formation of intergrown aggregates from the colloidal nanobeta particles provides own highly developed textural mesoporosity that makes the contribution of the diffusional alleviation of the support negligible.
Keywords: Supported colloidal nanocrystals; Mesoporous aluminosilicates MCM-41; N2 adsorption; Textural mesoporosity; Toluene disproportionation;

Palladium (Pd) nanoparticles were electrochemically dispersed on single-walled carbon nanotubes (SWNTs) by electroreduction of octahedral Pd(IV) complex formed on the SWNT surface. The structure and nature of the resulting Pd–SWNT composites were characterized by transmission electron microscopy and X-ray diffraction. The electrocatalytic properties of the Pd/SWNT electrode for hydrazine oxidation have been investigated by cyclic voltammetry; high electrocatalytic activity of the Pd/SWNT electrode can be observed. This may be attributed to the high dispersion of palladium catalysts and the particular properties of SWNT supports. The results imply that the Pd–SWNT composite has good potential applications in fuel cells.
Keywords: SWNTs; Palladium nanoparticles; Electrocatalysis; Hydrazine;

Polyamic acid (PAA) containing free-base porphyrin and zinc(II) porphyrin chromophores was synthesized by copolymerization of diphenylether-type tetracarboxylic dianhydride and diamines. The monolayer of the alkylamine salts of PAA (PAASs) at the air/water interface was deposited on solid substrates by the Langmuir–Blodgett (LB) technique. The PAAS LB films thus obtained were converted to polyimide (PI) LB films by chemical treatment. The fluorescence of porphyrin moieties in the PI LB film was observed, because of the weak electron-accepting properties of the diphenylether unit. Therefore, the photophysically important processes, such as photoinduced electron transfer, excitation energy transfer, and excitation energy migration could be investigated in relation to the layered nanostructures of the ultrathin PI films. The fluorescence spectrum suggested that the aggregation of porphyrin moieties in the PI LB films was effectively prevented by the use of polymeric films. The surface plasmon (SP) measurement showed that the thickness of the monolayers was 0.9–1.0 nm for PAAS films and 0.32–0.40 nm on average for PI LB films. The absorption dichroism of the Soret band of porphyrin indicated that porphyrin moieties in the PAAS and PI LB films are oriented in parallel with the substrate. These results showed that the orientation and the spatial distribution of porphyrin units can be efficiently regulated in the PI LB films in a nanometer dimension.
Keywords: Langmuir–Blodgett films; Polyimide; Porphyrin; Orientation; Excitation energy transfer;

Membrane potential across anion-exchange membranes in acidic solution system by Naomichi Kimura; Hidetoshi Matsumoto; Yuichi Konosu; Ryotaro Yamamoto; Mie Minagawa; Akihiko Tanioka (288-293).
The membrane potential across anion-exchange membranes in H2SO4 and Na2SO4 solutions was measured, and the experimental results were fitted to the theory in the 2–1 electrolyte system based on the Donnan equilibrium and the Nernst–Planck flux equations. For the Na2SO4 solution, the Donnan potential makes a significant contribution to the membrane potential, but for the H2SO4 solution, the diffusion potential significantly contributes to the membrane potential. The diffusion potential has a greater contribution to the membrane potential across AEM-2 with a high water content than that across AEM-1. These results suggest that a proton with a high mobility can move without substantial influence of electrostatic interaction in a positively charged membrane.
Keywords: Membrane potential; Anion-exchange membrane; Acidic solution;

Clay liners are charged membranes and show semipermeable behavior regarding the flow of fluids, electrical charge, chemicals and heat. At zero gradients of temperature and hydrostatic pressure, a salt concentration gradient across a compacted clay sample induces not only an osmotic flux of water and diffusion of salt across the membrane but also an electrical potential gradient, defined as membrane potential. Laboratory experiments were performed on commercially available bentonite samples in a rigid-wall permeameter connected to two electrically insulated fluid reservoirs filled with NaCl solutions of different concentrations and equipped with Ag/AgCl electrodes to measure the electrical potential gradient. The effect of membrane potential could be cancelled out by short-circuiting the clay with the so-called virtual shortcut. The potential gradient across the sample is brought to zero with a negative feedback circuit. It was observed that the water flux and the diffusion of Cl were hindered by the occurrence of a membrane potential, indicating that an electroosmotic counterflow is induced. Flow parameters were calculated with modified coupled flow equations of irreversible thermodynamics. They were in excellent agreement with values reported in the literature. Comparing the method of short-circuiting with a study elsewhere, where the electrodes were physically short-circuited, it was shown that the virtual shortcut is more appropriate because physically short-circuiting induces additional effects that are attributed to the fluxes.
Keywords: Bentonite; Clay membrane; Coupled flow equations; Diffusion; Irreversible thermodynamics; Membrane potential; Osmosis; Short-circuiting;

Adsorption of silanes bearing nitrogenated Lewis bases on SiO2/Si (100) model surfaces by Juliana Salvador Andresa; Rafael Machado Reis; Eduardo Perez Gonzalez; Leonardo Silva Santos; Marcos Nogueira Eberlin; Pedro Augusto de Paula Nascente; Sonia Tomie Tanimoto; Sérgio Antônio Spínola Machado; Ubirajara P. Rodrigues-Filho (303-309).
The present paper describes the one-pot procedure for the formation of self-assembled thin films of two silanes on the model oxidized silicon wafer, SiO2/Si. SiO2/Si is a model system for other surfaces, such as glass, quartz, aerosol, and silica gel. MALDI-TOF MS with and without a matrix, XPS, and AFM have confirmed the formation of self-assembled thin films of both 3-imidazolylpropyltrimethoxysilane (3-IPTS) and 4-(N-propyltriethoxysilane-imino)pyridine (4-PTSIP) on the SiO2/Si surface after 30 min. Longer adsorption times lead to the deposition of nonreacted 3-IPTS precursors and the formation of agglomerates on the 3-IPTS monolayer. The formation of 4-PTSIP self-assembled layers on SiO2/Si is also demonstrated. The present results for the flat SiO2/Si surface can lead to a better understanding of the formation of a stationary phase for affinity chromatography as well as transition-metal-supported catalysts on silica and their relationship with surface roughness and ordering. The 3-IPTS and 4-PTSIP modified SiO2/Si wafers can also be envisaged as possible built-on-silicon thin-layer chromatography (TLC) extraction devices for metal determination or N-heterocycle analytes, such as histidine and histamine, with “on-spot” MALDI-TOF MS detection.
Keywords: 3-Imidazolylpropyltrimethoxysilane; 4-(N-Propyltriethoxysilane-imino)pyridine; XPS; AFM; MALDI-TOF MS; Self-assembled thin films; Silicon dioxide; Silicon wafer;

A refractive tilting-plate technique for measurement of dynamic contact angles by Gregory T. Smedley; Donald E. Coles (310-318).
The contact angle is a critical parameter in liquid interface dynamics ranging from liquid spreading on a solid surface on earth to liquid motion in partially filled containers in space. A refractive tilting-plate technique employing a scanning laser beam is developed to conduct an experimental study of a moving contact line, with the intention of making accurate measurements of the contact angle. The technique shows promise as an accurate and potentially fully automated means to determine the velocity dependence of the contact angle at the intersection of the interface between two transparent fluids with a transparent solid surface. Ray tracing calculations are included to reinforce the measurement concept. The principal experiments were conducted at speeds ranging from 0.05 to 1.00 mm/s, both advancing and receding, using an immiscible liquid pair (nonane/formamide) in contact with glass. The contact angle was found to depend for practical purposes only on the sign of the velocity and not on its magnitude for the range of velocities studied. Other observations revealed a bimodal behavior of the contact line that depends on which liquid first contacts the glass, with resulting drift in the dynamic contact angle with time.
Keywords: Dynamic contact angle; Tilting plate; Refraction; Laser scan; Immiscible interface;

Nonlinear evolution of thin liquid films dewetting near soft elastomeric layers by Omar K. Matar; Vasileios Gkanis; Satish Kumar (319-332).
The nonlinear evolution of thin liquid films dewetting near soft elastomeric layers is examined in this work. Evolution equations are derived by applying the lubrication approximation and assuming that van der Waals forces in the liquid cause the dewetting and that the solid can be described as a linear viscoelastic material. Two cases are examined: (i) a liquid layer resting on an elastomer bounded from below by a rigid substrate, and (ii) an elastomer overlying a thin liquid film bounded from below by a rigid substrate. Linear stability analysis is carried out to obtain asymptotic relations which are then compared against solutions of the full characteristic equations. In the liquid-on-solid case, numerical solutions of the evolution equations show that van der Waals forces cause thinning of the liquid film and thickening of the elastomeric solid beneath film depressions. Inclusion of a short-range repulsive force suggests that regular patterns may form in which ridges of fluid rest on depressions in the solid. In the solid-on-liquid case, the van der Waals forces cause the solid layer to break up before the liquid film can dewet. The results presented here support the idea that the dewetting of thin liquid films might be exploited to create topographically patterned surfaces on soft polymeric solids.
Keywords: Thin films; Dewetting; Rupture; Lubrication; Viscoelastic; Elastomer; Gel;

The influence of flotation agent concentration on the wettability and flotability of polystyrene by Pavlína Basařová; Lidmila Bartovská; Karel Kořínek; David Horn (333-338).
The fundamental flotation process is the formation of a flocculant by air bubbles and solid particles in an aqueous solution. The behavior of plastic particles is significantly influenced by the wettability of the plastics. In this article the reciprocal relationship between the flotability and wettability of polystyrene was studied at different concentrations of flotation agents, particularly terpineol, polyethylene glycol dodecyl ether, tannic acid, and calcium lignosulfonate. The conclusions obtained demonstrate the dissimilar action of flotation depressants, what means different adhesion mechanisms on a plastic surface.
Keywords: Plastics flotation; Contact angle; Surface tension; Polystyrene;

Surface thermodynamic properties of polyelectrolyte multilayers by Stefan Köstler; Angel V. Delgado; Volker Ribitsch (339-348).
Multilayer architectures of polyelectrolytes fabricated by the layer-by-layer technique (LbL) on pretreated polymeric and inorganic substrates were studied by contact angle measurements. Poly(diallyldimethylammonium chloride), PDADMAC, and poly(sodium 4-styrenesulfonate), PSS, were used as polyelectrolytes. Contact angle data were used to calculate the van der Waals and Lewis acid–base components of the surface tension of the investigated surfaces. Knowledge of these quantities provides valuable information on surface composition, coating density, and possible interactions of the surface with other substances. Unusual wetting behavior of PDADMAC layers upon prewetting of the multilayer surfaces was found and described in terms of surface tension changes. A model of polymer chain rearrangement upon wetting was proposed to explain this behavior.
Keywords: Surface tension components; PDADMAC; PSS; Polyelectrolyte; Layer-by-layer deposition; Polymer substrates; Contact angle; Wetting;

Surface thermodynamic functions (surface entropy, surface enthalpy, and surface composition) of dilute solutions of 2-, 3-, and 4-methylcyclohexanol in ethylene glycol were obtained using surface tension measurements at various temperatures. Surface excess values and surface mole fractions were obtained from Gibbs equation and extended Langmuir model respectively. The results show that all methylcyclohexanols are surface active in ethylene glycol. The lyophobicity of solutes decreases with increasing temperature. The presence of a maximum point in the surface entropy diagram in all systems is explained by the formation of clathrate-like solvates at the surface of these systems.
Keywords: Surface tension; Surface thermodynamics; Methylcyclohexanol; Ethylene glycol; Clathrate-like solvates;

Solubilization by different-sized surfactant mixtures by Shigehiro Yamaguchi (355-359).
The solubilization phenomenon was investigated in mixed surfactant systems. The solubilization power of a mixed surfactant reaches its maximum at a particular temperature at each mixing ratio of surfactants. When the mole fraction of C4E1 in the total surfactant ( w 1 value) was varied in a water/C12E5/C4E1/decane system, the minimum mole fraction of total surfactant in the system necessary to obtain a single microemulsion phase (ξ value) was almost unchanged for w 1 < 0.3 , whereas it increased remarkably for w 1 > 0.8 . The molar solubilization capacity ( C s = ( 1 − ξ ) / ξ ) of the mixed surfactant decreased remarkably for w 1 < 0.3 , whereas it decreased gradually for w 1 > 0.8 . The result | d ξ / d w 1 | w 1 < 0.3 < | d ξ / d w 1 | w 1 > 0.8 is due largely to the characteristic of the function ξ ( C s ) = 1 / ( 1 + C s ) , specifically, | d ξ / d C s | w 1 < 0.3 < | d ξ / d C s | w 1 > 0.8 , where d ξ / d w 1 = ( d ξ / d C s ) ( d C s / d w 1 ) . The partial molar solubilization capacity ( C ¯ s ) of C4E1 was negative at almost all w 1 , but the C ¯ s value of C12E5 went through a maximum on the addition of C4E1. Propanol (a cosurfactant) has the same effect on the solubilization phenomenon in the water/C12E6/propanol/heptane system. In the water/C12E5/C12E7/decane system, the C ¯ s value of each surfactant did not vary greatly as the mixing ratio of surfactants was varied. The C s and ξ values were close to molar additivity for each mixing ratio.
Keywords: Solubilization; Different-sized surfactant system; C4E1; Molar solubilization capacity; Partial molar solubilization capacity;

PFGSE–NMR study of the self-diffusion of sucrose fatty acid monoesters in water by Valérie Molinier; Bernard Fenet; Juliette Fitremann; Alain Bouchu; Yves Queneau (360-368).
The micellization of pure monosubstituted sucrose fatty acid esters in water, namely sucrose octanoate, sucrose decanoate, sucrose laurate, sucrose dodec-5-cis-enoate, sucrose myristate, and sucrose palmitate, has been investigated by means of two NMR methods, pulsed field gradient spin-echo NMR (PFGSE–NMR), giving access to the self-diffusion coefficients of free molecules and micelles in solution, and the ERETIC method (electronic reference to access in vivo concentrations) for the measurement of concentrations by external calibration of a synthetic NMR signal. The early micellar regions and, when possible, the premicellar regions were investigated. By this method, we obtained the hydrodynamic radii of micelles, displaying a linear progression in relation to the chain length and an accurate determination of critical micellar concentration (CMC) for each sucrose ester. The effect of the regiochemistry of fatty chain grafting has been investigated, showing special behavior for 1 ′ -O-sucrose palmitate.
Keywords: Sugar; Carbohydrate; Sucrose ester; Alkylglucoside; Diffusion; Micelles; Surfactant; Unsaturated; Fatty acid;

Mixed micelle behavior of Pluronic L64 and Triton X-100 with conventional and dimeric cationic surfactants by Mandeep Singh Bakshi; Shweta Sachar; Kulbir Singh; Arifa Shaheen (369-377).
The mixed micellar properties of a triblock copolymer, Pluronic L64, (EO)13(PO)30(EO)13, and a nonionic surfactant, Triton X-100, in aqueous solution with conventional alkyl ammonium bromides and their dimeric homologues were investigated with the help of fluorescence and cloud point measurements. The composition of mixed micelles and the interaction parameter, β, evaluated from the critical micelle concentration (cmc) data for different mixtures using Rubingh's and Motomura's theories are discussed. It has been observed that the mixed micelle formation between monomeric/dimeric alkyl ammonium bromides and L64 was due to synergistic interactions which increase with the increase in hydrophobicity of the cationic component. On the other hand, synergistic mixing was observed in the mixed micelles of Triton X-100 and monomeric cationic surfactants, the magnitude of which decreases slightly with the increase in hydrophobicity of the cationic component. Antagonistic interactions were observed in the case of Triton X-100 and dimeric cationic surfactants.
Keywords: Alkyl ammonium surfactants; Triblock copolymer; Triton X-100; Mixed micelles; Fluorescence measurements;

Drop deformation dynamics and gel kinetics in a co-flowing water-in-oil system by Bernhard Walther; Carsten Cramer; Armin Tiemeyer; Lars Hamberg; Peter Fischer; Erich J. Windhab; Anne-Marie Hermansson (378-386).
Drop deformation and superimposed gel kinetics were studied in a fast continuous-flow process for a water-in-oil system. Highly monodisperse drops were generated in a double capillary and then deformed passing through a narrowing rectangular channel geometry. Nongelling deformation experiments were used to establish the process and compare it with existing theories. Thereafter, temperature induced drop gelation was included to study its effect on deformation and gel kinetics on short timescales and at high temperature gradients. The disperse phase was a κ-carrageenan solution with additional sodium and potassium ions for gelation experiments. Sunflower oil was used for the continuous phases. Nongelling experiments showed that shear forces are able to deform drops into ellipsoids. A comparison with the small deformation theory by Taylor was surprisingly good even when drop deformation and flow conditions were not in steady state. Superimposed gelation on the deformation process showed clearly the impact of the altered rheological properties of the dispersed and continuous phase. Deformation first increased on cooling the continuous phase until the onset of gel formation, where a pronounced decrease in deformation due to increasing droplet viscosity/viscoelasticity was observed. Drop deformation analyses were then used to detect differences in gelation kinetics at high cooling rate within process times as short as 1.8 s.
Keywords: Drop deformation; Shear flow; Gelation; Viscoelasticity; Viscosity; Carrageenan;

The miscibility and interactions between components in mixed adsorbed films and micelles containing zwitterionic (dodecyl sulfobetaine—DSB) and cationic (dodecyltrimethylammonium bromide) or anionic (sodium dodecyl sulfonate) surfactant, respectively, have been investigated. The molecular interactions have been quantified by the values of the excess free energy of adsorption ( Δ G S , Exc ) and micelle formation ( Δ G M , Exc ). The obtained results indicate nonideal behavior of the investigated mixtures since the values of Δ G S , Exc and Δ G M , Exc are negative. Moreover, it has been found that DSB interact more strongly with anionic surfactant as compared to cationic surfactant owing to different structure of mixed monolayers and micelles.
Keywords: Zwitterionic surfactants; Mixed adsorbed films; Mixed micelles; Motomura theory; Excess free energy of adsorption and micelle formation;

Sedimentation of a cylindrical particle in a Carreau fluid by Jyh-Ping Hsu; Ching-Feng Shie; Shiojenn Tseng (392-399).
The drag coefficient of an isolated, rigid cylindrical particle in a Carreau fluid is evaluated. The result of numerical simulation reveals that, in general, the shear-thinning nature of a Carreau fluid yields a drag coefficient smaller than that for the corresponding Newtonian fluid. Also, the smaller the Reynolds number, the more appreciable the decrease of the drag coefficient as the relaxation time constant of the Carreau fluid increases. The influence of the index parameter of a Carreau fluid on the drag coefficient depends largely on the magnitude of the relaxation time constant and is insensitive to the Reynolds number. Only if the relaxation time constant is sufficiently large is the influence of the index parameter on the drag coefficient significant. If the Reynolds number and/or the relaxation time constant is sufficiently large, the flow field upstream of a particle becomes asymmetric to that downstream. In general, the influence of the index parameter, the relaxation time constant, and the Reynolds number on the flow field follows the order index parameter < relaxation time constant < Reynolds number.
Keywords: Sedimentation; Cylindrical particle; Carreau fluid; Drag coefficient;

A network model, originally designed for an electrokinetic study of soft particle suspensions, has been used for an in-depth analysis of the physical behavior of these systems under the action of an externally applied DC electric field. The versatility of the network simulation method used makes it possible to obtain information readily not only about the electrophoretic mobility, but also about any physical variable of interest at all points around the suspended particle: electric potential, ion concentrations, fluid velocity. The field-induced polarization of the double layer is described in terms of the dependence of these and other derived variables (volume charge density, electric field components, ion flux components) on the distance to the membrane–solution interface. In contrast to colloidal suspensions of hard particles, which basically depend on just two parameters (the reciprocal Debye length multiplied by the particle radius, κa, and the zeta potential, ζ), soft particle suspensions require a wider parameter set. First, there are two characteristic diffusion lengths in the system (one inside the membrane and the other in the solution) and two geometrical lengths (the core radius a and the membrane thickness ( b − a )). Furthermore, there is the fixed charge density inside the membrane (and possibly a surface charge density over the core) that cannot be represented by a ζ potential. Finally, the parameter that characterizes the interaction between the fluid and the permeable membrane, γ, strongly influences the behavior of the system. Dependences on all these parameters (except the geometrical ones) are included in this study.
Keywords: Soft particles; Charged membranes; Spherical particles; Network simulation method; Velocity profiles; DC electric field;

The interaction of pairs of bubbles with equal diameters grown on adjacent capillaries in aqueous magnesium sulfate solutions is studied by varying electrolyte concentration and bubble diameter by Tsang, Koh and Koch [Y.H. Tsang, Y.-H. Koh, D.L. Koch, J. Colloid Interface Sci. 275 (2004) 290] (referred to as TKK hereafter). They find that the critical concentration to prevent coalescence, C t , increases as the equivalent diameter, d eq , decreases. In fact, C t is found to scale as d eq −1.2 . This dependence is stronger than that predicted by Prince and Blanch ( C t ∼ d eq −0.5 ) (referred to as PB [M.J. Prince, H.W. Blanch, AIChE J. 36 (1990) 1425] hereafter) on the basis of a postulation that lubrication pressure due to Marangoni stresses inhibit coalescence. TKK postulate instead that bubbles are stabilized by hydration structures. We further illustrate here that when hydration force term is added to the equation of motion of the film thinning process, predicted values of critical concentration are found to scale as d eq −1 . The current prediction shows a much better agreement with the experimental results than that proposed by PB. This suggests previous assumption that immobility of the interface by Marangoni effect as the dominant mechanism of inhibition of coalescence in an electrolytic solution is inaccurate [M.J. Prince, H.W. Blanch, AIChE J. 36 (1990) 1425, G. Marrucci, Chem. Eng. Sci. 24 (1969) 975].
Keywords: Bubble coalescence; Electrolytes; Critical concentration; Hydration force;

Organic/inorganic hybrid nano-microstructured coatings on insulated substrates by electrospray deposition by Hidetoshi Matsumoto; Tomoya Mizukoshi; Kazuya Nitta; Mie Minagawa; Akihiko Tanioka; Yutaka Yamagata (414-416).
Organic/inorganic hybrid nano-microstructured coatings on insulated polymer films were prepared by electrospray deposition (ESD) from an acrylic resin/silica sol blend solution. The surface morphologies of the coated films were observed using scanning electron microscopy (SEM). The SEM images showed that a nano-microscaled fibrous structure was formed on the film. The fiber diameter decreased from 4.4 μm to 600 nm with the increase in the silica sol content. Energy-dispersive X-ray analysis also revealed that silica atoms were homogeneously distributed in the fibrous structure on the polymer film. These results indicated that the ESD method is potentially a useful option for producing nano-microstructured coatings on not only conductive, but also insulating surfaces.
Keywords: Electrospray deposition; Organic/inorganic hybrid; Multifunctional coating; Nano-microstructure;

Effect of ozone treatment on ammonia removal of activated carbons by Soo-Jin Park; Sung-Yeol Jin (417-419).
In this work, activated carbons (ACs) were modified by ozone treatment to enhance the efficiency of removal of ammonia gas over the ACs. Surface properties of the ACs were confirmed by X-ray photoelectron spectroscopy (XPS) analysis and N2 adsorption isotherms at 77 K were investigated by BET and D–A methods to characterize the specific surface area, total pore volume, and micropore volume. The ammonia removal efficiency was confirmed by the gas-detecting tube technique. The results showed that the specific surface area and micropore volume of ACs were slightly destroyed as the ozone treatment time increased. However, the ozone treatment led to an increase in ammonia removal efficiency of ACs, mainly due to an increase of acid functional groups, such as carbonyl and ether groups, on carbon surfaces. It was revealed that the improvement of ammonia removal efficiency of ACs was greatly affected by the interfacial acid–base interactions between modified ACs and basic ammonia adsorbate.
Keywords: Activated carbons; Ozone treatment; Ammonia removal; Oxygen functional groups;

A new method for bidimensional analysis of interferometric patterns of liquid films by Rui Nogueira; Rosa Vazquez; José Luís Mata; Benilde Saramago (420-423).
A new method for bidimensional analysis of interferometric patterns of wetting liquid films obtained with the captive bubble technique is described. This method replaces one-dimensional analysis along various intensity profiles with analysis of one average intensity profile. The advantage is to concentrate the surface characteristics of the whole film image into a single intensity profile.
Keywords: Wetting films; Interferometry; Captive bubble technique; Bidimensional analysis; Film thickness;

by Arthur Hubbard (424).