Journal of Colloid And Interface Science (v.285, #2)

The electrochemical multilayer films of crown-shaped polyoxomolybdate Na21{[Na5(H2O)14]∩[MoV 20MoVI 26O134(OH)10(μ-CH3COO)4]}⋅CH3COONa⋅90H2O (Mo46) and polyelectrolytes by layer-by-layer assembly were investigated. The stable multilayer films were assembled by alternate adsorption of negatively charged POM and positively charged polyelectrolytes is from their aqueous dispersions. UV–vis spectroscopy and cyclic voltammetry were used to monitor the regular growth of the multilayer films. The multilayer films-modified ITO electrode was used for the detection of electrocatalytic activity toward the reduction of nitrite, bromate, and hydrogen peroxide. The proposed novel immobilized method exhibited good stability, reproducibility and high sensitivity for the determination of electrocatalytic, which is important for practical application.
Keywords: Polyoxometalate; Indium tin oxide-coated glass electrodes (ITO); Layer-by-layer; Ultrathin multilayer film; Electrochemical behavior;

This study investigates the feasibility of using ethylene oxide (EO) chain adsorption to determine the surface area of smectite in water. Experimental results indicate that high-molecular-weight poly(ethylene oxide) (PEO) should be used to provide reasonable estimations for monolayer capacity of PEO on smectite. The surface areas of smectites in water are calculated from the monolayer capacity of PEO adsorbed on smectite by taking the area per EO unit as 8.05 Å2. The method measures the actual surface area of smectite exposed when dispersed in water, which is important to applications of smectite under aqueous conditions.
Keywords: Surface area; Smectite; Adsorption; Ethylene oxide chain;

The study of the effect of pH on phosphate sorption by different trophic lake sediments by Shengrui Wang; Xiangcan Jin; Yan Pang; Haichao Zhao; Xiaoning Zhou (448-457).
This paper studies the effect of pH on phosphate sorption by the sediments of different trophic lakes, including sorption isotherms with different pH values, their effect on sorption rate, their impact on the kinetics of sorption and desorption. The following conclusions are drawn. (1) The phosphate sorption capacity of lake sediment is correlated with pH, but not with its trophic level; that is, pH at 7.0 > 5.5 > 9.0. The three isotherms models cannot well describe phosphate sorption by different trophic sediments with different pH, and its applicability seems irregular. (2) The power function equation is one of the best kinetic models, which can provide satisfactory fitting of the kinetic data of phosphate sorption by different trophic sediments, and there is no obvious difference between them. The quick phosphate sorption by the sediment takes place mainly at 0–0.5 h, the pH value has a remarkable effect on the rate of phosphate sorption by the sediment, and sediments in different trophic states tend to have similar trends of change, with pH 5.5 > 7.0 > 9.0. (3) The effect of pH on phosphate sorption shows a similar trend for different trophic sediments; namely, as pH increases phosphate sorption rate tends to increases sharply at first and then drop suddenly. After a while it increases slightly, and finally a slight decrease follows as the pH increases. The maximum and minimum of phosphate sorption capacity may be attributed to the rate of phosphate release. (4) Phosphate sorption by lake sediments is not completely reversible and strong bonding occurs between sediment particles and sorbed phosphate. This makes it difficult for the sorbed phosphate to be desorbed from the sediments. The amounts of desorbed phosphate are almost the same in different trophic sediments with different initial pH values; that is, the effect of pH on phosphate desorption is small.
Keywords: pH; Phosphate; Sorption; Isotherm; Kinetics; Lake sediment;

Neutron reflectivity (NR) was used to study the adsorption of human serum albumin and human fibrinogen on quartz. The proteins were individually and sequentially adsorbed from heavy water and heavy water/methanol mixtures at pH 4 and 7.0. The technique allows for the subnanometer resolution of the adsorbed layer thickness and gross morphology. Under the conditions of our measurements we found that fibrinogen formed a distinct layer that we interpret as a mat of the protein three layers thick whereas albumin formed only diffuse layers. The adsorption pattern of the two proteins changed radically when one protein was adsorbed on top of the other (previously adsorbed). In general our measurements indicate that the adsorbed protein layers on quartz are rather loosely bound and that these layers, incorporating as much as 80% water, extend further into the bulk fluid than might have been expected.
Keywords: Protein adsorption; Neutron reflectivity; Fibrinogen; Albumin; Sequential adsorption;

Rheological behavior of organic suspensions of fluorapatite by Kamel Chaari; Jamel Bouaziz; Khaled Bouzouita (469-475).
A fluorapatite suspension prepared in the azeotrope methyl ethyl ketone–ethyl alcohol (MEK:EtOH) in the presence of the phosphoric ester was investigated. Electrical conductivity, adsorption isotherms, and sedimentation technique showed that the amount of phosphoric ester adsorbed on the fluorapatite surface was equal to, or higher than, 1 wt%. This dispersant concentration led to a good particle packing. The rheological properties of fluorapatite suspensions were studied as a function of phosphoric ester concentration. The data obtained from the viscosity measurements and those previously collected correlated well. In the case of suspensions prepared with 60 wt% in fluorapatite, the dispersion was optimal for a phosphoric ester content of about 1.3 wt%.
Keywords: Electrical conductivity; Rheology; Fluorapatite; Phosphate ester; Organic medium;

Effects of pH and ionic strength on the adsorption of phosphate and arsenate at the goethite–water interface by Juan Antelo; Marcelo Avena; Sarah Fiol; Rocío López; Florencio Arce (476-486).
The surface properties of a well-crystallized synthetic goethite have been studied by acid–base potentiometric titrations, electrophoresis, and phosphate and arsenate adsorption isotherms at different pH and electrolyte concentrations. The PZC and IEP of the studied goethite were 9.3 ± 0.1 and 9.3 ± 0.2 , respectively. Phosphate and arsenate adsorption decrease as the pH increases in either 0.1 or 0.01 M KNO3 solutions. Phosphate adsorption is more sensitive to changes in pH and ionic strength than that of arsenate. The combined effects of pH and ionic strength result in higher phosphate adsorption in acidic media at most ionic strengths, but result in lower phosphate adsorption in basic media and low ionic strengths. The CD-MUSIC model yields rather good fit of the experimental data. For phosphate it was necessary to postulate the presence of three inner-sphere surface complexes (monodentate nonprotonated, bidentate nonprotonated, and bidentate protonated). In contrast, arsenate could be well described by postulating only the presence of the two bidenate species. A small improvement of the arsenate adsorption data could be achieved by assuming the presence of a monodentate protonated species. Model predictions are in agreement with spectroscopic evidence, which suggest, especially for the case of arsenate, that mainly bidentate inner-sphere complexes are formed at the goethite–water interface.
Keywords: Phosphate adsorption; Arsenate adsorption; Oxide–water interface; Surface charge; Electrophoretic mobilities; CD-MUSIC model;

Selective adsorption of thiophene and 1-benzothiophene on metal-ion-exchanged zeolites in organic medium by Mei Xue; Ramesh Chitrakar; Kohji Sakane; Takahiro Hirotsu; Kenta Ooi; Yuji Yoshimura; Qi Feng; Naoto Sumida (487-492).
Adsorption of the organic sulfur compounds thiophene (TP) and 1-benzothiophene (1-BTP) in an organic model solution of hydrodesulfurizated gasoline (heptane with 1 wt% toluene and 0.156 mM (5 ppmw as sulfur) TP or 1-BTP) was studied by a batch method at 80 °C using metal-ion-exchanged Y-zeolites. Although NaY-zeolite or its acid-treated material rarely adsorbed the organic sulfur compounds, NaY-zeolites exchanged with Ag+, Cu2+, and Ce3+ ions and NH4Y-zeolites exchanged with Ce3+ ions showed markedly high adsorptive capacities for TP and 1-BTP. The sulfur uptake increased in the order CuY-zeolite(Na) < AgY-zeolite(Na) < CeY-zeolite(Na) for both the organic sulfur compounds. The adsorption isotherms for TP and 1-BTP followed the Langmuir's relationship and the saturation capacities by CeY-zeolite(Na) were calculated as 0.022 and 0.033   mmol / g , respectively. The mole ratios of TP/Ce and 1-BTP/Ce were 0.031 and 0.047, respectively. CeY-zeolite(NH4) which was prepared from NH4Y-zeolite showed less uptake of TP and 1-BTP than CeY-zeolite(Na), probably due to its lower cerium content.
Keywords: Metal ion; Zeolite; Selective adsorption; Thiophene; Benzothiophene; Organic sulfur; Gasoline;

Co-adsorption of cadmium(II) and glyphosate at the water–manganite (γ-MnOOH) interface by Madeleine Ramstedt; Caroline Norgren; Andrei Shchukarev; Staffan Sjöberg; Per Persson (493-501).
The co-adsorption of Cd(II) and glyphosate (N-(phosphonomethyl)glycine, PMG) at the manganite (γ-MnOOH) surface has been studied in the pH range 6–10 at 25 °C and with 0.1 M Na(Cl) as ionic medium. Batch adsorption experiments, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and extended X-ray absorption fine structure (EXAFS) spectroscopy were used for the quantitative analysis and the determination of the molecular structure of the surface complexes. The adsorption of Cd(II) and PMG in the ternary Cd(II)–PMG–manganite system was compared with the adsorption in the binary Cd(II)–manganite and PMG–manganite systems. The formation of three inner sphere surface complexes was observed, a ternary Cd(II)–PMG–manganite complex, a binary Cd(II)–manganite complex and a binary PMG–manganite complex. The surface concentration of the ternary complex and the Cd(II)–manganite complex was more or less constant throughout the pH range studied. However, the surface concentration of the binary PMG–manganite complex decreased with increasing pH. The major part of the binary PMG–surface complex was protonated. The ternary surface complex displayed a type B structure (Cd(II)–PMG–manganite). The average Cd–Mn distance obtained from EXAFS (3.26 Å) indicates that the binary and ternary Cd(II)–surface complexes are formed by edge-sharing of Mn and Cd octahedra on the (010) plane of the manganite crystals.
Keywords: N-(phosphonomethyl)glycine; Glyphosate; Manganite; γ-MnOOH; Cadmium; EXAFS; XPS; FTIR; Ternary surface complexes;

Multilayer adsorption of amino acids on oxidized cellulose by Dmitry S. Zimnitsky; Tatiana L. Yurkshtovich; Pavel M. Bychkovsky (502-508).
The adsorption of amino acids (AA) (glycine, L-alanine, L-proline) on oxidized cellulose (OC) with various carboxyl contents and degrees of crystallinity from aqueous and water/ethanol solutions was studied. It was found that multilayer adsorption occurs in concentrated solutions of AA. It proceeds according to successive mechanisms via adsorption of AA zwitterions onto carboxyls of already adsorbed AA. This leads to formation of chain AA associates in the OC phase. A sharp increase in swelling accompanies multilayer adsorption. It was established that structural characteristics and degree of polymerization of OC are the main factors that affect multilayer adsorption. The distribution of carboxyls in the OC phase also plays an important role. Multilayer adsorption does not proceed in water/ethanol solutions and in the case of the cationic form of AA.
Keywords: Adsorption; Amino acids; Oxidized cellulose; Multilayer; FT-IR; Crystallinity; Degree of polymerization;

Understanding anion adsorption mechanisms is necessary to allow prediction of anion adsorption behavior. This study was conducted to evaluate the ability of the triple layer model, a chemical surface complexation model, to describe the effect of changes in solution ionic strength (0.01–1.0 M NaCl) and solution pH (3–11) on B adsorption by the iron oxide, goethite, the aluminum oxide, gibbsite, the clay minerals, kaolinite and montmorillonite, and two arid zone soils. Ionic strength dependence of adsorption suggests an inner-sphere adsorption mechanism for goethite, kaolinite, montmorillonite, and the two soils and an outer-sphere adsorption mechanism for gibbsite. The triple layer model, containing an inner-sphere adsorption mechanism, was able to describe B adsorption on goethite, kaolinite, montmorillonite, and the two soils. The model was able to describe B adsorption on gibbsite using an outer-sphere adsorption mechanism. A problematic inconsistency exists in the triple layer model description of ionic strength dependent B adsorption between the type of B surface complex defined in the model and the ionic strength dependence of the model result. That is, postulating an inner-sphere adsorption mechanism in the triple layer model resulted in an ionic strength dependence appropriate for the formation of outer-sphere surface complexes and vice versa. Additional tests of the ability of the triple layer model to describe ionic strength dependent adsorption of additional ions are needed to establish whether the inconsistencies are limited to the B system or are of concern in other triple layer model applications.
Keywords: Surface complexation modeling; Inner-sphere surface complex; Outer-sphere surface complex; Goethite; Gibbsite; Kaolinite; Montmorillonite; Soil;

Desorption of chloroorganic compounds from a bed of activated carbon by Robert Pełech; Eugeniusz Milchert; Agnieszka Wróblewska (518-524).
The desorption of 1,2-dichloroethane from a bed of DTO activated carbon after adsorption from aqueous solution has been investigated. The desorption process was carried out using steam. The basic characteristics of the process were determined. The studies were performed in the temperature range 100–160 °C. A steam consumption indicator reduces with an increase of temperature from 100 to 140 °C. An elevation of temperature above 140 °C does not cause an improvement in the desorption efficiency. The number of performed cycles does not reduce the adsorption capacity of used activated carbon. Studies on the regeneration of the bed saturated with a seven-component mixture of chloroorganic compounds at temperature of 140 °C were carried out. The degree of removal of the sum of chloro-derivatives exceeded 0.96 at a volume ratio of steam (recalculated on the condensate) to bed of about 10. It was found that the dechlorination proceeds during desorption at elevated temperature. The quantitative ratio of chloro-derivatives in the desorbate was changed in comparison to the composition of wastewater directed to the adsorption.
Keywords: Desorption; Chloroorganic compounds; Activated carbon; Wastewater;

The influence of the adsorbent amount on the changes in molecular mass distribution of polymers under adsorption from mixtures by Yuri Lipatov; Valentine Chornaya; Tamara Todosijchuk; Galina Dudarenko (525-531).
Changes in the molecular mass distribution (MMD) for polymer as a result of adsorption from binary and ternary solutions have been studied by the exclusion chromatography method. It was found that the affinity of polymer components to a surface has a crucial influence on the changes in MMD of polymers. The diminution of polydispersity in solutions after adsorption was observed for two polymers. In the case of the polar polymer poly(butyl methacrylate) (PBMA) the diminution of polydispersity is caused mainly by the preferential adsorption of low-molecular-mass fractions, whereas in the case of the nonpolar polymer polystyrene (PS) it is caused by the transition of the high-molecular-mass fractions onto the adsorbent surface. The analysis of experimental results indicates that the quantity of the adsorbent affects the composition of the adsorption layer formed by polymers of different chemical nature.
Keywords: Polydispersity of polymers; Molecular mass distribution (MMD); Adsorbent/solution ratio (A/V); Low-molecular-mass fractions; High-molecular-mass fractions;

Nanocomposites are the emerging materials of the 21st century in view of their possessing design uniqueness without any compromises, certain unusual property combinations that are not found in conventional composites, as well as a wide spectrum of applications. Polymer-based layered compound nanocomposites have special place in view of their best property enhancement. Hence, the objective of this article is to bring new ideas to optimize the design of polymer/layered compounds/fibrous nanocomposites, starting with a brief overview of the preparation, structure, properties and applications. The proposed strategy suggests the use of synthetic and natural layered compounds, taking into account their ability to be exfoliated in the form of single layers, which can be chemically grafted with key molecules. The same procedure can also be applied to fibrous materials. These surface-grafted molecules can carry reactive groups to be bonded to the polymer matrices. Thus adhesion between the reinforcement and the polymer matrix can be achieved. This methodology, which has not been explored systematically in the specialized literature, can be used to produce polymer nanocomposites with low-cost fibrous materials having similarity to expensive carbon nanotubes exhibiting optimized dispersion, interfacial bonding, and attractive physical and other properties.
Keywords: Layered compounds; Single layers; Natural fibrous materials; Exfoliation; Polymer nanocomposites; Grafting;

Morphology characterization of layer-by-layer films from PAH/MA-co-DR13: the role of film thickness by Nara C. de Souza; Valtencir Zucolotto; Josmary R. Silva; Felipe R. Santos; David S. dos Santos; Débora T. Balogh; Osvaldo N. Oliveira; José A. Giacometti (544-550).
We report on the use of dynamic scale theory and fractal analyses in the study of distinct growth stages of layer-by-layer (LBL) films of poly(allylamine hydrochloride) (PAH) and a side-chain-substituted azobenzene copolymer (Ma-co-DR13). The LBL films were adsorbed on glass substrates and characterized with atomic force microscopy with the Ma-co-DR13 at the top layer. The granular morphology exhibited by the films allowed the observation of the growth process inside and outside the grains. The growth outside the grains was found to follow the Kardar–Parisi–Zhang model, with fractal dimensions of ca. 2.6. One could expect that inside the grains the morphology would be close to a Euclidian surface with fractal dimension of ca. 2 for any growth stage. The latter, however, was observed only for thicker films containing more than 10 bilayers. For thinner films the morphology was well described by a self-affine fractal. Such dependence of the growth behavior with the film thickness is associated with a more complete coverage of adsorption sites in thicker films due to diffusion of polymer molecules.
Keywords: Layer-by-layer; Dynamic scale theory; Morphology;

Thermal stability of organic monolayers chemically grafted to minerals by Jeffrey McElwee; Roy Helmy; Alexander Y. Fadeev (551-556).
The thermal degradation of monolayers of alkylsilicon hydrides (RSiH3), alkylphosphonic acids (RP(O)(OH)2), and alkyldimethylchlorosilanes (R(CH3)2SiCl) supported on silica, alumina, titania, zirconia, and calcium hydroxyapatite particles was investigated using thermal gravimetric analysis (TGA). The common feature in the TGA was a dramatic weight loss between ∼200 and ∼600 °C (N2 atmosphere), which was not present for bare minerals, and, thus, was assigned to the degradation of the surface grafted organic species. The onset of weight loss and the temperature of maximal weight loss rate ( T MAX ) showed no dependence on the mineral and were determined by the nature of the chemical group directly attached to the surface. The T MAX values were ∼ 400 – 450  °C (monolayers of RSiH3 and RP(O)(OH)2) and ∼250 °C (monolayers of RSi(CH3)2Cl). The activation energies ( E A ) of the degradation processes were determined using TGA at multiple heating rates. Surprisingly, the substrate material did not show a significant effect on E A . For example, all the monolayers of octadecyl groups (R = C18H37) supported on silica, alumina, titania, and zirconia showed closed E A values ∼ 265 ± 15   kJ / mol . The weight loss, IR, MS, and chemical analysis data suggested that monolayer degradation occurred through pyrolysis of the hydrocarbon moieties (R groups) via cleavage of the C―C and Si―C (monolayers of silanes) or C―C and P―C bonds (monolayers of phosphonic acids). The inorganic portion of the molecule remained attached to the surface of the mineral (presumably as silicates or phosphates).
Keywords: Thermal stability; TGA; Alkylsilane; Alkylphosphonic acid; Self-assembled monolayer; Metal oxide; Titania; Silica; Zirconia; Calcium hydroxyapatite;

Determination of surface charge properties of PC-12 cells by electrophoresis by Tai-Horng Young; Chih-Huang Hung; Shih-Wei Huang; Tien-Shing Hsieh; Jyh-Ping Hsu (557-561).
The electrophoretic behavior of pheochromocytoma (PC-12) cells was investigated both experimentally and theoretically. Cell mobility in aqueous media at different pHs and ionic concentrations was measured, and a model, which assumed that the cell surface contains both acidic and basic functional groups, was proposed. As a result, it was revealed that the experimental data gathered can be described satisfactorily by assuming that the cell surface contains two types of monovalent acidic functional groups and one basic functional group. The values of the dissociation constants of the acidic and basic groups are found to be close to those of acidic amino acids, which indicates that the acidic amino acids may play an important role in the surface electrical properties of PC-12 cells.
Keywords: Electrophoresis; Surface charge; PC-12 cells;

Fluorescence probing of albumin–surfactant interaction by Swati De; Agnishwar Girigoswami; Susmita Das (562-573).
Protein–surfactant interactions were studied using bovine serum albumin (BSA) and the three surfactants sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB), and poly(oxyethylene)isooctyl phenyl ether (TX-100). The surfactants used belong to three broad classes, i.e., anionic, cationic, and nonionic. These categories of surfactants were used to elucidate the mechanism of surfactant binding to BSA, at pH 7. The interactions were followed fluorimetrically using both intrinsic tryptophan (Trp) fluorescence and the fluorescence of an external label. The aggregation behavior of the surfactants were studied in the presence of BSA. Steady-state fluorescence studies indicate that all three surfactants bind to BSA in a cooperative manner. This cooperative binding affects the binding of the external label to BSA. All these effects are also manifested in time-resolved fluorescence studies. The effects of surfactants on acrylamide quenching and energy transfer from Trp in BSA to bound dye provided valuable insights into the structural modification of BSA in presence of surfactants. The surfactant-induced conformational change of BSA was also confirmed by circular dichroism studies. However, among the three categories of surfactants, the nonionic surfactant shows the least interaction with BSA.
Keywords: Protein; Surfactant; Cooperative binding; Energy transfer; Quenching;

Polysaccharides as a template for silicate generated by sol–gel processes by Yu.A. Shchipunov; A. Kojima; T. Imae (574-580).
The polysaccharides, as established previously (Yu.A. Shchipunov, J. Colloid Interface Sci. 268 (2003) 68; Yu.A. Shchipunov, T.Yu. Karpenko, Langmuir 20 (2004) 3882), can manipulate the formation of hybrid silica nanocomposites by sol–gel processes. Here atomic force microscopy was applied to show whether carbohydrate macromolecules serve as a template for silicate. Mica was used as a substrate to adsorb polysaccharide. It was found that its surface is not neutral to the sol–gel processes, providing the silica precipitation. To hinder it, the mica was protected by a monomolecular film of arachidic acid with the help of a Langmuir–Blodgett technique. Hydrophobically modified cationic hydrohyethylcellulose was adsorbed from a diluted aqueous solution. It was demonstrated that the carbohydrate macromolecules located on the hydrophobic surface did promote silica precipitation, serving as a template.
Keywords: Sol–gel; Polysaccharide; Mineralization; Hybrid silica nanocomposite; Biomaterial;

Contamination by larger particles of two almost-uniform latices: analysis by combined dynamic light scattering and turbidimetry by Verónica D.G. Gonzalez; Luis M. Gugliotta; Jorge R. Vega; Gregorio R. Meira (581-589).
Multiangle dynamic light scattering (MDLS) and turbidimetry (T) were applied (both individually and combined) for determining the contamination by larger particles of two almost-uniform polystyrene (PS) latices. Latex 1 was synthesized in our laboratories, and it contained a main population diameter of 340 nm together with a small fraction of larger particles. This latex was used as the base material for producing an immunoassay kit. Latex 2 was obtained by a simple blend of two uniform PS standards. The proposed data treatment calculates the diameter and number fraction of the large particles contamination assuming that the PSDs are bimodal. The calculation involves minimizing the errors between the measurements and their theoretical predictions. When analyzed by combined MDLS–T, the contamination of Latex 1 involved number fraction 0.6% and particle diameter 865 nm. The T average diameter is a function of the measurement wavelength, and the highest deviations of this average to an increasing contamination by large particles were always observed at the higher wavelengths. The DLS average diameter is a function of the measurement angle, but in this case it is impossible to determine a priori the angle of observation that provides the largest deviation of this average diameter to an increasing contamination.
Keywords: Multiangle DLS; Turbidimetry; Monodisperse latex;

Design and characterization of a new drug nanocarrier made from solid–liquid lipid mixtures by Marcos Garcia-Fuentes; Maria J. Alonso; Dolores Torres (590-598).
The classical lipid nanoparticles that have been proposed for drug delivery are composed of solid lipids. Due to their composition, these nanoparticles have a limited drug loading and controlled release capacity. The present work was aimed at modifying the inner structure of nanoparticles made of tripalmitin, lecithin, and poly(ethylene glycol) (PEG)-stearate with the incorporation of a liquid lipid (Miglyol 812 oil). The composition and structural organization of the components of the resulting nanoparticles were characterized by 1H NMR spectroscopy. Any possible changes in the crystalline domains of individual components when in the form of the nanoparticles were investigated by differential scanning calorimetry (DSC) and X-ray diffraction spectroscopy. The results of the NMR analysis indicated a significant incorporation of the oil to the solid nanoparticle matrix. Furthermore, the relaxation time constants as well as the peak width of the 1H NMR spectrum of the nanoparticles suggest the presence of the oil in the form of phase-separated liquid nanoreservoirs within the nanoparticles. This conclusion was supported by the observation of restricted diffusion dynamics for the oil molecules. Interestingly, the incorporation of the oil did not interfere with the crystallization of the solid lipids (tripalmitin and PEG-stearate). In conclusion, a new nanostructure consisting of solid lipids and oily nanodomains was developed. This structural modification of the solid lipid nanoparticles may have an effect on their encapsulation capacity and controlled release properties.
Keywords: Lipid nanoparticles; Nanostructures; NMR; Solid–liquid lipid matrices; Restricted diffusion; Relaxation-time constants;

Fractal structure of asphaltene aggregates by Nazmul H.G. Rahmani; Tadeusz Dabros; Jacob H. Masliyah (599-608).
A photographic technique coupled with image analysis was used to measure the size and fractal dimension of asphaltene aggregates formed in toluene–heptane solvent mixtures. First, asphaltene aggregates were examined in a Couette device and the fractal-like aggregate structures were quantified using boundary fractal dimension. The evolution of the floc structure with time was monitored. The relative rates of shear-induced aggregation and fragmentation/restructuring determine the steady-state floc structure. The average floc structure became more compact or more organized as the floc size distribution attained steady state. Moreover, the higher the shear rate is, the more compact the floc structure is at steady state. Second, the fractal dimensions of asphaltene aggregates were also determined in a free-settling test. The experimentally determined terminal settling velocities and characteristic lengths of the aggregates were utilized to estimate the 2D and 3D fractal dimensions. The size–density fractal dimension ( D 3 ) of the asphaltene aggregates was estimated to be in the range from 1.06 to 1.41. This relatively low fractal dimension suggests that the asphaltene aggregates are highly porous and very tenuous. The aggregates have a structure with extremely low space-filling capacity.
Keywords: Asphaltene; Bitumen; Structure; Fractal; Couette; Aggregation; Fragmentation; Floc; Settling;

In this paper, we show that the far field electrostatic potential created by a highly charged finite size cylinder within the nonlinear Poisson–Boltzmann (PB) theory, is remarkably close to the potential created within the linearized PB approximation by the same object at a well-chosen fixed potential. Comparing the nonlinear electrostatic potential with its linear counterpart associated to a fixed potential boundary condition (called the effective surface potential), we deduce the effective charge of the highly charged cylinder. Values of the effective surface potential are provided as a function of the bare surface charge and Debye length of the ionic solution. This allows to compute the anisotropic electrostatic interaction energy of two distant finite rods.
Keywords: Nonlinear Poisson–Boltzmann theory; Linear Poisson–Boltzmann theory; Charged finite rods; Effective surface potential; Effective charge; Electrostatic interaction energy;

Highly fluorescent polymer particles were prepared with Eu β-diketonates complex as a fluorophore by miniemulsion polymerization technique. Eu β-diketonates complex has a long decay time, a large Stokes shift, and very narrow emission bands in comparison with other organic fluorescent compounds. Aqueous miniemulsion was prepared by mixing monomer, crosslinker, hydrophobe, and Eu β-diketonates complex and then putting the mixture into an aqueous solution of surfactant, followed by ultrasonication. An aqueous solution of initiator was added to the miniemulsion to obtain fluorescent polymer particles, which were monodispersed without aggregation. Particle size was decreased to deca-nano scale by increasing the amount of surfactant. Fluorescent intensity was increased by using Eu β-complex coordinated with additional ligand. Further fluorescence quantum yields and fluorescent properties in the presence of DNA were investigated to the confirm superiority of Eu β-diketonates complexes in polymer particles.
Keywords: Miniemulsion polymerization; Eu β-diketonates complex; Decananosized fluorescent particle;

In this study, we consider the ideal aggregate with quadratically increasing permeability κ = k 2 r 2 and derive the analytical expression of the stream function within the porous aggregate by incorporating the Brinkman and continuity equations. The hydrodynamic properties of the aggregate are investigated by taking account of the hydrodynamic radius, settling velocity, and fluid collection efficiency, which are found to be solely dependent on the permeability prefactor k 2 . The fractal dimension D f and prefactor k 2 of the ideal aggregate are found to be 5 / 3 (=1.67) and 0.20, respectively, and well describe the hydrodynamics of aggregates formed in the diffusion-limited-cluster-aggregation (DLCA) regime. More important, hydrodynamic similarity between the ideal aggregate and impermeable solid sphere is discovered in terms of variations of the hydrodynamic radius, settling velocity, and fluid collection efficiency with respect to the aggregate radius.
Keywords: Aggregation; Fractal aggregate; Permeability; Settling velocity; Hydrodynamic radius;

Studies on 2D hybrid films of half surfactant-covered Au nanoparticles at the air/water interface by Shufeng Pang; Oikawa Tetsuya; Watanabe Tomoyuki; Takeshi Kondo; Takeshi Kawai (634-639).
A hybrid monolayer film of Au nanoparticles, half-covered with dioctadecyldimethylammonium chloride (DODAC), was prepared at the air/water interface and characterized using transmission electron microscopy (TEM), a quartz-crystal microbalance, and infrared spectra measurements. TEM images of the hybrid film showed that the distribution of Au nanoparticles depends on the surface density of DODAC and reaction time. IR spectral data provided evidence for a surface-enhanced effect of the Au nanoparticles. The wavenumber of CH2-stretch vibrations of DODAC in the infrared external reflection spectra revealed that the DODAC molecules were adsorbed onto the Au nanoparticles in a close-packed crystalline state for any surface density of DODAC, which is different from the usual behavior of Langmuir monolayers.
Keywords: Hybrid monolayer; TEM; QCM; FTIR; DODAC; Gold nanoparticles;

Interactions of Pluronics with phospholipid monolayers at the air–water interface by Lin-Chau Chang; Chia-Yu Lin; Min-Wen Kuo; Churn-Shiouh Gau (640-652).
Pluronics are triblock copolymers which are extensively applied excipients shown to interact with cell membranes. The aim of our study was to apply monolayer techniques and epifluorescence microscopy to investigate the interaction behavior between selected Pluronics and phospholipid monolayers which serve as a model of cell membranes. The results showed that Pluronic L61 with hydrophobic proportions much larger than those of F68 demonstrated condensed film-like surface behavior while F68 exhibited more expanded behavior. The increments of surface pressure and the changes of image were more obvious in adding Pluronic L61 than F68 to the subphase of dipalmitoylphosphatidylcholine (DPPC) monolayers, which indicated that the interaction may be related to van der Waals forces and hydrophobic interaction. Pluronics selected with higher hydrophobicities demonstrated larger surface activities and penetration abilities while being added to the subphase of DPPC and dimyristoylphosphatidylcholine (DMPC) monolayers. Pluronic P85 and F68 were found to be squeezed to subphase at higher surface pressures, which may be attributed to their relatively higher hydrophilicities.
Keywords: Pluronics; Phospholipid monolayers; Hydrophobicity;

Surface characterization of heat-treated electrolytic manganese dioxide by Aaron P. Malloy; Gregory J. Browning; Scott W. Donne (653-664).
In this work a titration technique was used to determine the amphoteric surface properties of a series of heat-treated electrolytic manganese dioxide (EMD) samples (up to 500 °C). The surface of each sample was found to consist of independent acidic and basic hydroxyl sites, which could be characterized by their respective equilibrium constants and site concentrations. It was found that the acidic sites could not be characterized by a single equilibrium constant, but rather by a distribution indicating the subtle differences between individual sites, while a single equilibrium constant adequately represented the basic sites. For EMD, K a varied between 0.1 and 6.3 × 10 −5 , with a corresponding [Mn―OH(a)T] value varying between 9.1 and 6.4 × 10 −6   mol m −2 over the pH range considered. K b and [Mn―OH(b)T] were found to be 1.81 × 10 −9 and 1.93 × 10 −5   mol m −2 , respectively. With heat treatment, K a increased, suggesting a strengthening of the Mn―O bond via the removal of defects such as Mn3+ ions and cation vacancies. The fact that K b also increased was initially counterintuitive because it suggested that the Mn―O bond had been weakened by heat treatment. However, assuming that the acidic and basic hydroxyl groups are independent, the trends in K b could be rationalized in terms of oxygen ion coordination in the progressively heat-treated samples. The number of surface sites ( N s ) was determined crystallographically and from the sum [Mn―OH(a)T] + [Mn―OH(b)T]. The data from both methods were of the same order of magnitude but exhibited different trends due to certain inadequacies in both methods. However, the data trends did indicate that the crystal planes at the particle surface could be changing with heat treatment due to a decrease in the value of N s determined from the surface titrations. Electrochemical analysis of the samples in 9 M KOH indicated that their performance degraded considerably with heat treatment. In comparison with the surface titration data, it was concluded that proton insertion into the structure occurred only through basic surface sites, the decreasing number of which could limit performance.
Keywords: Manganese dioxide; Surface titrations; Surface hydroxyl groups; Battery materials;

On the adsorption of cetyldimethylbenzylammonium chloride at the mercury/electrolyte solution interface by Antonis Avranas; Natálie Sedláčková; Efi Malasidou (665-673).
The adsorption of cetyldimethylbenzylammonium chloride (CDBACl) on the hanging mercury electrode is studied in various supporting electrolytes at various temperatures from 1 to 50 °C. A condensed film with low capacitance is formed at negative potentials at transition temperatures below approximately 40 °C. The decrease of the temperature favors the film formation, and increases the width of the capacitance pit, while its value remains practically constant. Hysteresis phenomena are also observed during different scan directions. Capacitance–time curves at the potentials where the film is formed show in some cases a nucleation and growth mechanism with induction time and studied by the Avrami formulation. At high temperatures an increase of the capacitance with time is observed depending on the CDBACl concentration and slightly on the electrolyte used, and is attributed to the formation of hemimicelles. At high negative potentials a second narrow region with lower capacitance values is observed. This is easily observed at very high temperatures, while it is absent at lower temperatures. It depends upon the concentration of CDBACl and the electrolyte used. The results are different from those obtained for the adsorption of cetyltrimethylammonium bromide on mercury, indicating the importance of interaction between the hydrophobic chains.
Keywords: Cetyldimethylbenzylammonium chloride; Differential capacitance; Condensed film; Nucleation; Hemimicelle;

From a microwave flash-synthesized TiO2 colloidal suspension to TiO2 thin films by E. Gressel-Michel; D. Chaumont; D. Stuerga (674-679).
Titanium(IV) oxide thin films have been prepared by dip-coating at ambient temperature from a TiO2 colloidal suspension. Prior to deposition, this suspension was synthesized by microwave-induced thermal hydrolysis of a titanium tetrachloride aqueous solution in the presence of hydrochloric acid. The effects, on film roughness and film thickness, of substrate, number of layers, substrate withdrawal speed, and heat treatment temperature were investigated on different observation scales. The microwave-born oxide nanoparticles showed good affinity to glass and silicon substrates; 10- to 50-nm-thick thin films, with absorption edge blue-shifted compared to bulk anatase, were obtained through a simple process without the need of heating treatment for crystallization purposes.
Keywords: TiO2; Thin films; Dip-coating; Colloidal suspension; Oxide nanoparticles; Microwave synthesis; Thermohydrolysis;

Supramolecular chirality of the hydrogen-bonded complex Langmuir–Blodgett film of achiral barbituric acid and melamine by Xin Huang; Chao Li; Siguang Jiang; Xuesong Wang; Baowen Zhang; Minghua Liu (680-685).
Complex monolayers of barbituric acid and melamine were formed by spreading a chloroform solution of amphiphilic barbituric acid on the subphase of melamine solution. It was confirmed that the complex monolayer was formed through in situ complementary hydrogen bonding at the air–water interface. It was interesting to find that the complex LB films showed supramolecular chirality although both of the molecules were achiral, as verified by the circular dichroism spectral measurements. It was suggested that the ππ stacking of the neighboring barbituric acid and melamine group in a helical sense resulted in the chirality of the molecular assemblies. Due to the directionality of the hydrogen bonding, the BA-M film could form regular aligned nanofibers on the AFM images. Increasing the subphase temperature will lead to the decrease of CD intensity and the change of the morphologies. We suggested that the strength of the hydrogen bonding resulted in the difference.
Keywords: Barbituric acid; Circular dichroism; Hydrogen bonding; LB film; Supramolecular chirality;

Conditions for depositions of multiple LB films for different divalent cations were determined experimentally at the p K A of the system. The p K A of the fatty acid–subphase salt system is the pH at which half of the fatty acid heads are dissociated. Stable Y-type depositions take place in full immersion/removal cycles. Under certain conditions, full depositions occur only during the downstroke (X-type) or during the upstroke (Z-type). Experiments show a clear trend between p K A of the system and loss of stability of Y-depositions toward full depositions taking place during immersion only, i.e., YX transitions. Stable Y-type depositions can be achieved for most divalent cations at large dipping speeds. Dipping speed necessary to maintain stable Y-depositions depend on the p K A of the system; the lower the p K A the larger the dipping speed. The accumulated time spent by the solid substrate under the water subphase is not a good indicator of YX transition because the number of dipping cycles is also a relevant variable. For a given number of cycles, the lower regions of the solid substrate are most affected by transition because they spent a larger time under the water subphase.
Keywords: Langmuir–Blodgett films; YX transition; Counterions; Subphase pH;

Surface potentials and ionization equilibrium in Y-type deposition of multiple Langmuir–Blodgett films by M. Elena Diaz Martin; F. Javier Montes; Ramon L. Cerro (694-702).

Microstructural investigation of monoglyceride–water coagel systems by NMR and CryoSEM by John P.M. van Duynhoven; Ilka Broekmann; Arjen Sein; Geert M.P. van Kempen; Gert-Jan W. Goudappel; Wiebren S. Veeman (703-710).
Monoglyceride coagels consist of a network of plate-like crystals and are formed from a swollen gel state (α-gel). In order to resolve the transition mechanism, coagels were prepared with monoglycerides that differ in fatty acid composition (monomyristate and palmitate/stearate, respectively). Rheology provided information on kinetics of coagel formation and the strength of the resulting crystal network. From NMR measurements, the surface-to-volume ratio, tortuosity, and dimensionality of the network were obtained. These findings were in line with qualitative and quantitative structural information obtained from CryoSEM. As a model for the behaviour of non-monoglyceride species, the dynamics of (perdeuterated) palmitic acid was monitored in both α-gels and coagels. The experimental data support a two-stage mechanism. In the first stage, two-dimensional separation of D- and L-isomers in the monoglyceride bilayers of the α-gel occurs. This process depends primarily on lateral diffusion rate of the monoglycerides. Palmitic acid can be accommodated in the α-gel bilayer, but in the coagels it is separated into relative mobile and mechanically weak junction zones between the crystal plates. In the second stage of coagel formation, the crystal plates also grow in the third dimension. Both monoglyceride type and concentration determine the kinetics of this process.
Keywords: Self-diffusion; Image analysis; Coagels; Nuclear magnetic resonance;

Oligo(ethylene glycol)-terminated thin films were prepared by photo-induced hydrosilylation of α-hepta-(ethylene glycol) methyl ω-undecenyl ether (EG7) on hydrogen-terminated silicon (111) and (100) surfaces. Their resistance to protein adsorption, and stabilities (from hours to days) under a wide variety of conditions, such as air, water, biological buffer, acid, and base, were investigated using contact-angle goniometry and ellipsometry techniques. Results indicated higher stability of the films chemisorbed on Si(111) than on Si(100). Furthermore, micron-sized patterns were fabricated on the films via AFM anodization lithography. Using atomic force microscopy (AFM) and fluorescence microscopy, we demonstrated that various proteins including fibrinogen, avidin, and bovine serum albumin (BSA) predominately adsorbed onto the patterns, but not the rest of the film surfaces.
Keywords: Oligo(ethylene glycol)-terminated thin films; Hydrogen-terminated silicon surfaces; Photo-induced surface hydrosilylation; Protein adsorption; AFM anodization lithography; Stability;

Study of individual Na-montmorillonite particles size, morphology, and apparent charge by A. Cadene; S. Durand-Vidal; P. Turq; J. Brendle (719-730).
Size, morphology, and apparent charge of individual Na-montmorillonite particles of natural MX-80 sodium montmorillonite were investigated in the present study by the use of three coupling methods. In the first part of this work, natural and synthetic montmorillonite clays were studied with atomic force microscopy (AFM) and photo-correlation spectroscopy (PCS). Both techniques exhibit the presence of two clay populations with a high dispersion of the length distribution. Microscopic analysis of the system revealed that clay particles could be reasonably approximated at low concentrations to ellipsoidal tactoids about 1.2 nm high. Average dimensions of the first population were typically 320–400 nm long/250 nm wide and 200–250 nm long/120 nm wide for natural and synthetic clays, respectively. The second population exhibits smaller sizes: 65 and 50 nm long and 35 and 25 nm wide for natural and synthetic clays, respectively. The statistics obtained for natural clay were then verified by PCS experiments on sodium montmorillonite suspensions. Both techniques reveal an important length dispersion. However, the relative proportions of the two kinds of particles could not be established properly because of both lack of statistics and limitations of the employed techniques. In the following part, conductivity measurements were performed on dilute montmorillonite clay suspensions. Raw data were then interpreted with the sizes and morphological information gained in the first part of the present work. The apparent charge of the clay sheets was found to be 8% of the structural charge.
Keywords: Montmorillonite; Sheets; Tactoids; Aggregates; Morphology; Size distribution; Apparent charge; AFM; PCS; Conductivity;

The delamination and intercalation of a layered microporous aluminophosphate, [Al3P4O16]3−⋅3[CH3(CH2)NH3]+ (AlP), with aromatic amine have been carried out and were followed by XRD and SEM measurements. The basicity of the amine plays an important role in this process, as do the dielectric constant of the solution and the amount of amine added. A saturated benzylamine (p K a of 9.34) intercalate of the aluminophosphate are obtained in solutions with dielectric constant of 50–70 and an amine concentration of 10 mmol/g AlP, while no aniline (p K a of 4.60) intercalates are formed under similar conditions. The remarkable effect of basicity of the amine can be explained by a metathetical balanced reaction model, which was proved by the results of the intercalation processes of 4-methylpiridine (p K a = 6.00 ) and 4-methylimidazole (p K a = 7.55 ).
Keywords: Layered microporous aluminophosphate; Delamination; Aromatic amine intercalation; Basicity;

Experimental investigation on thermocapillary drop migration at large Marangoni number in reduced gravity by Jing-Chang Xie; Hai Lin; Pu Zhang; Fang Liu; Wen-Rui Hu (737-743).
Results from a space experiment on thermocapillary drop migration conducted on board the Chinese spacecraft ShenZhou-4 are presented in this paper. In the experiment, isolated drops of Fluorinert liquid moved in a matrix liquid of 5cst silicone oil at values of the Marangoni numbers (Ma) ranging up to 5500 and the interferometry images showed the temperature distribution inside the test cell. The drop migration velocity was measured. The experimental results show that the scaled drop migration velocity V / V YGB obviously decreases with Ma increasing the values up to 5500. The space experimental results are also compared with those from our early experiments, other space experiments, and some theoretical predictions.
Keywords: Interfacial tension; Thermocapillary migration; Microgravity;

Nonlinear surface wave instability for electrified Kelvin fluids by Yusry O. El-Dib; Osama E. Abd El-Latif (744-759).
A weakly nonlinear approach is utilized here to discuss surface wave instability for two superposed electrified fluids of Kelvin type. The influence of a vertical electric field is discussed. The linear form for equations of motion is solved in the light of nonlinear boundary conditions. The method of multiple scales is used for the purpose of nonlinear perturbation. The surface wave response is governed by the well-known nonlinear Ginzburg–Landau equation rather than the transcendental dispersion relation in the linear scope. Although linear stability conditions are not available for arbitrary viscosity, the nonlinear analysis allowed deriving necessary and sufficient stability conditions. Moreover, at the marginal state, the nonlinear scope for stability is discussed through its dependence on the wavetrain frequency, in which short-wave disturbance is assumed to relax the linear transcendental terms. Besides the linear stability constraint, the nonlinear scope gives an additional constraint on the wavetrain frequency. Nonlinear stability criteria are derived and are performed in view of a nondimensional form. Furthermore, the nonlinear analysis is repeated for an arbitrary wave disturbance. A suitable choice for dimensionless form made it possible to relax transcendental terms included in stability conditions. Numerical calculations at the marginal state show that both the vertical electric field and the stratified fluid density play a dual role in the stability criteria. This dual role is the opposite to the dual role that the stratified viscosity plays in the stability profile. For the marginal state representation, numerical examination shows that elasticity plays a dual role in the stability criteria in a manner similar to that of the viscosity behavior.
Keywords: Nonlinear interfacial stability; Viscoelastic fluids; Electrified Kelvin fluids;

The impact of water droplets (diameter 3.6 mm) at a fixed Weber number of 59 on solid surfaces with precisely tailored surface wettabilities was studied experimentally using a high-speed imaging camera at 2500 frames per second. Solid surface wettability was varied using four fractional mixtures of self-assembled monolayers of 1-octadecanethiol and 16-mercaptohexadecanoic acid. The surfaces so obtained are characterized for contact angle and chemical functionality using the axisymmetric drop shape analysis profile (ADSA-P) technique and Fourier transform infrared spectroscopy (FT-IR). Our results correlate the wetting effects of the impacting droplets with the surface energy and contact angle measurements of the tailored surfaces. Literature models for the maximum spreading diameter are employed and compared with those from our experiments. An equation is also proposed for the maximum spreading diameter which makes use of the correct contact angles and results in the least error among the models considered. As a consequence of Young's equation, the correct contact angles to be used for droplet impact dynamics should be the corresponding advancing angles on a smooth substrate of interest. We also conclude that accurate examination of literature models requires careful experimentation on impact dynamic data on well-prepared and characterized surfaces such as those presented here.
Keywords: Droplet impact dynamics; Self-assembled monolayers; Spreading factor; Surface energetics; Contact angles;

This paper analyzes the effect of surfactant on the linear stability of an annular film in a capillary undergoing a time-periodic pressure gradient force. The annular film is thin compared to the radius of the tube. An asymptotic analysis yields a coupled set of equations with time-periodic coefficients for the perturbed fluid–fluid interface and the interfacial surfactant concentration. Wei and Rumschitzki (submitted for publication) previously showed that the interaction between a surfactant and a steady base flow could induce a more severe instability than a stationary base state. The present work demonstrates that time-periodic base flows can modify the features of the steady-flow-based instability, depending on surface tension, surfactant activity, and oscillatory frequency. For an oscillatory base flow (with zero mean), the growth rate decreases monotonically as the frequency increases. In the low-frequency limit, the growth rate approaches a maximum corresponding to the growth rate of a steady base flow having the same amplitude. In the high-frequency limit, the growth rate reaches a minimum corresponding to the growth rate in the limit of a stationary base state. The underlying mechanisms are explained in detail, and extension to other time-periodic forms is further exploited.
Keywords: Core–annular film flow; Time oscillatory; Capillary instability; Surfactant; Marangoni;

In the mid 1960s the present authors published two papers dealing with penetration of nonwetting liquids such as mercury into the interstitial void spaces using the model of uniform packed spheres. A circular arc was used to approximate the liquid–vapor interface in both papers. However, our circular arc–toroid values for the pressure–volume relationship in the pendular ring which exists between two touching spheres was criticized. The authors concluded that our approximation led to unacceptably large differences compared to the values calculated from the exact nodoid shape. This incorrect conclusion was never rebutted and has, in fact, been misinterpreted by subsequent workers to include values calculated for the shape of the access opening and the associated pressure for penetration into the void space of a collection of spheres. This leaves a cloud of uncertainty, not only over our original work on nonwetting fluids, but on the application of our procedures to the field of wetting fluids. The contrast in the geometrical shapes of the toroid and nodoid is depicted and the pressure values are compared at equal volumes. In contrast to the claim of excessive error, we show the toroid geometry, in conjunction with a pressure–volume work derivation, to have a maximum error of 0.06% as compared to the nodoid at all liquid–solid contact angles. The toroid also has the advantage of using a readily derived work versus surface free energy balance rather than requiring the use of incomplete elliptic integrals to evaluate the nodoid. Attempts to use radii of curvature to evaluate the toroid shape are shown to give extremely poor approximations of the exact values for the pressure. Values reported for access to the interior void space of a collection of spheres still need adjustment for the effect of contact angles between 0° and 180° for characterizing assemblies of real solids by computing “equivalent spherical” particle size from porosity and mercury penetration data. However, there is no anticipation that use of the circular arc will introduce large errors in the results. This gives confidence to us and others working with wetting media to test the potential applicability of the packed sphere model to various diverse fields.
Keywords: Spheres; Pores; Mercury porosimetry; Nonwetting liquids; Wetting liquids; Pendular rings; Nodoid; Toroid;

The kinetics of oxidation of some aminoalcohols (AA), viz. ethanolamine, diethanolamine, and triethanolamine, by N-bromosuccinimide (NBS) in alkaline medium has been investigated in the absence as well as in the presence of cetyltrimethylammonium bromide (CTAB), a cationic surfactant. The reaction always followed a first-order dependence of rate on NBS, while the order in each AA and alkali was found to decrease from unity to zero at higher [AA] and [OH], respectively. The reaction is strongly catalyzed by CTAB even before the critical micelle concentration (CMC) of CTAB. However, the observed rate constants attained constancy at higher [CTAB] (>CMC of CTAB). The premicellar kinetics has been rationalized in the light of the Piszkiewicz positive cooperativity model [J. Am. Chem. Soc. 99 (1977) 1550]. The binding constants between the reactants and the surfactant have also been evaluated using the Raghvan and Srinivasan model [Proc. Ind. Acad. Sci. 98 (1987) 199], which is applicable to bimolecular micellar catalyzed reaction and predicts constancy in the observed rate constant at higher [surfactant]. The binding constants obtained by both the models are in good agreement.
Keywords: Micellar aggregation; Oxidation of aminoalcohols; N-bromosuccinimide; Kinetics of;

Excess density in oilfield water—crude oil dispersions by Igor N. Evdokimov; Nikolaj Yu. Eliseev; Valerij A. Iktisanov (795-803).
Extensive density measurements were performed with mixtures of 12 degassed (dead) crude oils with respective oilfield brines (formation waters). All unprocessed samples were collected directly from wellheads and contained only indigenous surfactants, such as asphaltenes and fine solids. Nonzero excess densities and excess thermal expansions (evaluated on the assumption of quasi-binary water–oil mixtures) were observed for water cuts in the range from X = 0.4 to 0.6 at all studied temperatures T = 5 – 50 ° C . We suggest that these results are due to the formation of a dense asphaltene-mediated “middle phase” in the studied w/o dispersions. This suggestion is substantiated by plotting TX phase diagrams which topologically strongly resemble those conventionally observed in some standard Winsor III-type systems. The formation of a complexly structured “middle phase” has been directly verified by preliminary visual/microscopic studies of a phase separation in a crude oil–water mixture.
Keywords: Crude oil; Brine; Dispersion; Emulsion; Viscosity; Excess density; Middle phase; Bicontinuous phase; Asphaltenes;

Emulsification of oil in water as affected by different parameters by Musa Kaleem Baloch; Gulzar Hameed (804-813).
The aim of this investigation was to develop a basic understanding of the emulsification process by considering simple systems such as n-hexane, n-heptane, n-decane, and kerosene oil in water. The technique employed for the purpose was ultrasonification. The effect of ultrasonification time, chain length, viscosity, surface tension, oil content, and ionic strength of the media on the quality of emulsion has been studied. The emulsions were viewed through microscope to measure the number, size, and size distribution of droplets. Quantification of turbidity and viscosity was also used to characterize the emulsions. It has been found that the number and size of the droplets vary with the time of ultrasonification, contents of oils, molecular mass of the oils, and ionic strength of the media, and hence the quality of the emulsion is influenced by these parameters. The droplet size decreases, whereas the number of drops increases with the time of emulsification, approaching an optimum distribution at about 15 min of ultrasonification. Further, the increase in the molecular mass of the oil increases the size of the droplets and hence decreases the stability of the emulsion. The addition of electrolytes encourages coalescence and enhances the instability in the system. The results are in accord with the equations proposed by us.
Keywords: Emulsion; Immiscible liquids; Size and size distribution; Electroviscous effect; Coalescence; Ultrasonification time; n-Hexane; n-Heptane; n-Decane; Kerosene oil;

Anisotropic aggregation and phase transition in Langmuir monolayers of methyl/ethyl esters of 2,3-dihydroxy fatty acids by Liyan Wang; Sandra Jacobi; Jing Sun; Michael Overs; Harald Fuchs; Hans Juergen Schaefer; Xi Zhang; Jiacong Shen; Lifeng Chi (814-820).
We studied interfacial properties of a series of methyl and ethyl esters of enantioenriched syn-2,3-dihydroxy fatty acids with different chain lengths at the air–water interface, using a Langmuir type film balance and a Brewster angle microscope (BAM). After analyzing their surface pressure (Π)–area (A) isotherms, we inferred that these molecules existed as an E conformation in the liquid-expanded (LE) phase of monolayers, and the E conformation of molecules changed into a Z conformation during the LE–LC transition in a monolayer. BAM images evidenced the formation of elongated LC aggregates. This is possibly induced by the intermolecular hydrogen bonds, leading to the anisotropic growth of LC domains, on the basis of the FT-IR spectroscopy data. The enthalpy change of the LE–LC phase transition is considered to result from the three types of intermolecular interactions at the air–water interface during compression of these amphiphiles. These findings are discussed in terms of various physical factors that influenced intermolecular interactions and macroscopic aggregations of these amphiphiles.
Keywords: Amphiphile; Langmuir; Monolayer; Phase; Thermodynamics; Conformation;

Oilfield solids and water-in-oil emulsion stability by Danuta M. Sztukowski; Harvey W. Yarranton (821-833).
Model water-in-hydrocarbon emulsions consisting of toluene, heptane, water, asphaltenes, and native solids were used to investigate the role of native solids in the stability of oilfield emulsions. The solids were recovered from an oil-sands bitumen, a wellhead emulsion, and a refinery slop oil. The solids were clay platelets and fell into two size categories: (1) fine solids 50 to 500 nm in diameter and (2) coarse solids 1 to 10 μm in diameter. Emulsions stabilized by fine solids and asphaltenes were most stable at a 2:1 fractional area ratio of asphaltenes to solids. It appears that when the asphaltene surface coverage is high, insufficient solids remain to make an effective barrier. When the solids coverage is high, insufficient asphaltenes remain on the interface to immobilize the solids. Treatments that weaken the interface, such as toluene dilution, are recommended for emulsions stabilized by fine solids. Emulsions stabilized by coarse solids were unstable at low solids concentrations but became very stable at solids concentrations greater than 10 kg/m3. At low concentrations, these solids may act as bridges between water droplets and promote coalescence. At high concentrations, layers of coarse solids may become trapped between water droplets and prevent coalescence. Treatments that flocculate the solids, such as heptane dilution, are recommended for emulsions stabilized by high concentrations of coarse solids. It is possible that emulsions containing both types of solids may require more than one treatment, or even process step, for effective water resolution.
Keywords: Solids; Clays; Particle size distribution; Water-in-oil emulsions; Refinery emulsions; Wellhead emulsions; Stabilization mechanisms; Interfacial composition; Destabilization of emulsions;

DNA separation by EFFF in a microchannel by Zhi Chen; Anuj Chauhan (834-844).
This paper theoretically explores the application of electric field flow fractionation (EFFF) for the size-based separation of DNA strands in a microchannel. An axial electric field cannot separate DNA strands in solution because the electrical mobility of the strands is independent of the length. However, lateral electric fields coupled with an axial Poiseuille flow can separate the DNA strands of different sizes. By using regular perturbation analysis, we obtain the effective diffusivity and the mean velocity of the DNA molecules that are undergoing a pressure driven Poiseuille flow in a 2D channel in presence of a lateral electric field. The mean velocities and the dispersion coefficients are then utilized to determine the scaling for length of the channel and the time required for separation of DNA molecules in different parameter regimes. The results show that EFFF can separate DNA strands in the range of 10 kbp that differ in size by about 2.5 kbp in about half an hour in a 1 cm long channel. While DNA strands can be separated by EFFF, the performance of devices based on EFFF seems to be at best comparable to other techniques such as entropic trapping.
Keywords: Electrophoresis; EFFF; DNA separation; Microchannel; Lateral electric field;

Dielectrophoresis (DEP) is increasingly being explored as a means to manipulate or separate colloidal particles. The direction and strength of the DEP force depend strongly on the induced dipole strength, K, of a polarized particle, and predictions of DEP forces require carefully computed values for K. In this paper, we present the calculation of the dipole strength using the full electrokinetic theory of Mangelsdorf and White for both static and oscillating electric fields. The effects of particle zeta potential, radius, Debye length and electrolyte composition on the magnitude and sign of Re ( K ) are discussed. The full theory model is compared with the extended Maxwell–Wagner (EMW) model and the results show that the EMW model can fail to predict the full Re ( K ) variation with frequency, even predicting Re ( K ) with the incorrect sign depending on system parameters. A program for the dipole strength calculation shown in this paper is available from the authors.
Keywords: Dielectrophoresis; Electric polarizability; Induced dipole strength; Dielectric particle;

Electrophoresis of a rigid sphere in a Carreau fluid normal to a planar surface by Eric Lee; Chi-Tien Chen; Jyh-Ping Hsu (857-864).
The boundary effect on electrophoresis is investigated by considering the electrophoresis of a spherical particle in a non-Newtonian fluid normal to a planar surface under conditions of low surface potential and weak applied electric field. The Carreau model, which is widely used for the description of polymeric fluids of shear-thinning nature, is adopted to simulate the non-Newtonian behavior of the fluid. We show that, in general, shear thinning has the effect of raising the electrophoretic mobility of a particle. The thinner the double layer, the more significant this effect is, and, since the presence of the planar surface has the effect of enhancing the shear-thinning effect, the closer a particle is to the planar surface, the larger is its mobility. Both the shear rate and the viscosity of the fluid vary most significantly in the gap between the particle and the planar surface, and the maximal shear rate and the minimal viscosity occur on the particle surface.
Keywords: Electrophoresis; Boundary effect; Sphere normal to plane; Non-Newtonian fluid; Carreau model;

The boundary effect on the dynamic electrophoretic behavior of a charged entity is examined by considering a sphere in a spherical cavity. The present study extends previous analysis to the case of an arbitrary level of electrical potential where the effect of double-layer distortion can be significant. The governing equations are solved numerically based on a pseudo-spectral method, which is found to be sufficient in solving the corresponding electrophoresis problem when a static electric field is applied. The result of numerical simulation reveals that as the size of a cavity decreases, both the magnitude of the mobility and the inertial force acting on a particle decrease accordingly. Also, while the distortion of the ionic cloud should not be ignored, in general, when the surface potential of a particle is high, its influence on the magnitude and on the phase angle of the mobility is alleviated by the presence of the cavity.
Keywords: Dynamic mobility; Boundary effect; Sphere in spherical cavity; Arbitrary potential;

The ultralow interfacial tensions between crude oils and gemini surfactant solutions by Hong Chen; Lijuan Han; Pingya Luo; Zhongbin Ye (872-874).
In this paper, the interfacial tension between crude oil and solution of cationic gemini surfactant has been studied. It is found that the interfacial tension between crude oil and water is closely related to the nature of a gemini surfactant and oil; meanwhile, in the case without additives, some gemini surfactants or mixtures of some gemini surfactants can reduce the interfacial tension between crude oil and water to an ultralow value.
Keywords: Ultralow interfacial tension; Crude oil; Gemini surfactant;

Photochemical fabrication of a well-defined diblock copolymer nanotemplate using 172-nm vacuum ultraviolet light by Atsushi Hozumi; Shuichi Asakura; Akio Fuwa; Naoto Shirahata (875-878).
Well-ordered nanopore arrays were successfully prepared from polystyrene (PS) and poly(methyl methacrylate) (PMMA) diblock copolymer (DBC) film based on a photochemical approach using 172-nm vacuum ultraviolet (VUV) light. Since the etching selectivity between the PS and PMMA domains against activated oxygen species generated by the VUV irradiation of atmospheric oxygen molecules was markedly different, PMMA was preferentially decomposed, resulting in the formation of PS nanopore arrays. Both the photoetching rate and final morphology depended greatly on the atmospheric pressure during VUV irradiation. Since at 10 Pa the PS domains degraded less due to the shortage of oxygen molecules in the atmosphere, the residual matrix kept its fine nanostructures up to 40 min of irradiation. The matrix could be eliminated completely when irradiation was extended to 60 min at this pressure. On the other hand, at 103 Pa the DBC film was removed completely from the substrate within 10 min of irradiation. However, at 103 Pa, not only the decomposition of the PMMA domains, but also the photoetching rate of the PS domains accelerated significantly resulting in marked distortion of the generated nanostructures. By selecting an appropriate atmospheric pressure and time for VUV irradiation, we were able to control both nanoarray formation and elimination without the use of any physical and/or chemical treatment.
Keywords: 172-nm vacuum ultraviolet light; Diblock copolymer; Photoetching; Nanopore array;

Smooth approximations for structural force in thin fluid films near the critical point are presented to facilitate the usage of formulas derived in [J. Colloid Interface Sci. 278 (2004) 173–183] in experimental studies.
Keywords: Disjoining pressure; Critical point;