Journal of Colloid And Interface Science (v.305, #1)

Bilirubin adsorption on self-assembled phospholipid bilayers was studied using quartz crystal microbalance, and factors influencing its adsorption such as pH, temperature, and solution ionic strength were discussed in detail. The results show the amount of adsorbed bilirubin on self-assembled phospholipid bilayers is small at higher temperature and large at higher pH and solution ionic strength, and the adsorption kinetic parameter estimated from the in situ frequency measurement is ( 1.8 ± 0.27 ) × 10 6   M −1 (mean ± S.D.). With the present method, the desorption of adsorbed bilirubin caused by human serum albumin and the photoinduced decomposition of adsorbed bilirubin under light illumination were also examined. QCM measurement provides a useful method for monitoring the adsorption/desorption process of bilirubin on self-assembled phospholipid bilayers.Action mechanism of bilirubin on self-assembled phospholipid bilayers was investigated using quartz crystal microbalance.
Keywords: Phospholipid bilayer; Bilirubin; Adsorption; Quartz crystal microbalance;

The adsorption of different alkanes (linear and cyclic), aromatics, and chlorohydrocarbons onto different nonmicroporous carbons—multiwalled carbon nanotubes (CNTs), carbon nanofibers (CNFs), and high-surface-area graphites (HSAGs)—is studied in this work by inverse gas chromatography (IGC). Capacity of adsorption was derived from the isotherms of adsorption, whereas thermodynamic properties (enthalpy of adsorption, surface free energy characteristics) have been determined from chromatographic retention data. HSAGs present the highest adsorption capacity, followed by CNTs and CNFs (although CNTs present an intermediate surface area between the two HSAG studied). Among the different adsorbates tested, benzene exhibits the highest adsorption capacity, and the same trend is observed in the enthalpy of adsorption. From surface free energy data, enthalpies of adsorption of polar compounds were divided into dispersive and specific contributions. The interactions of cyclic (benzene and cyclohexane) and chlorinated compounds (trichloroethylene, tetrachloroethylene, and chloroform) with the surfaces are mainly dispersive over all the carbons tested, CNTs being the material with the highest dispersive contribution, as was deduced also from the entropy parameter. Adsorption parameters were correlated with morphological and chemical properties of the materials.Thermodynamic properties of the adsorption of volatile organic compounds onto carbon nanotubes, carbon nanofibers, and high-surface-area graphites are obtained by inverse gas chromatography.
Keywords: Carbon nanotubes; Carbon nanofibers; High-surface-area graphites; Adsorption;

Adsorption of hydrocarbons on organo-clays—Implications for oil spill remediation by Onuma Carmody; Ray Frost; Yunfei Xi; Serge Kokot (17-24).
Organo-clays synthesised by the ion exchange of sodium in Wyoming Na-montmorillonite (SWy-2-MMT) with three surfactants: (a) octadecyltrimethylammonium bromide (ODTMA), formula C21H46NBr; (b) dodecyldimethylammonium bromide (DDDMA), formula C22H48BrN; and (c) di(hydrogenated tallow)dimethylammonium chloride were tested for hydrocarbon adsorption. Using diesel, hydraulic oil, and engine oil an evaluation was made of the effectiveness of the sorbent materials for a range of hydrocarbon products that are likely to be involved in land-based oil spills. It was found that the hydrocarbon sorption capacity of the organo-clays depended upon the materials and surfactants used in the organo-clay synthesis. Greater adsorption was obtained if the surfactant contained two or more hydrocarbon long chains. Extensive utilisation of chemometrics principally with the aid of MCDM methods, produced models which consistently ranked the organo-clays well above any of the competitors including commercial benchmark materials. Thus, the use of organo-clays for cleaning up oil spills is feasible due to its many desirable properties such as high hydrocarbon sorption and retention capacities, hydrophobicity. The negative effects of the use of organo-clays for oil-spill cleanup are the cost, the biodegradability, and recyclability of the organo-clays.Based on the PROMETHEE modelling, the organo-clay sorbents clearly performed best on the hydrocarbon sorption capacity criteria when compared with benchmark reference sorbents. The MCDM analysis demonstrated that the use of organo-clays for cleaning up oil spills is feasible due to its many desirable properties such as high hydrocarbon sorption and retention capacities, and hydrophobicity.
Keywords: Hydrocarbon adsorption; Oil spills; Sorbents; Organo-clays; Chemometric analysis;

Competition between humic acid and carbonates for rare earth elements complexation by Olivier Pourret; Mélanie Davranche; Gérard Gruau; Aline Dia (25-31).
The competitive binding of rare earth elements (REE) to humic acid (HA) and carbonates was studied experimentally at various pH and alkalinity values by combining ultrafiltration and inductively coupled plasma mass spectrometry techniques. The results show that the REE species occur as binary humate or carbonate complexes but not as ternary REE–carbonate–humate as previously proposed. The results also reveal the strong pH and alkalinity dependence of the competition as well as the existence of a systematic fractionation across the REE series. Specifically, carbonate complexation is at a maximum at pH 10 and increase with increasing alkalinity and with the atomic number of the REE (LuCO3  ≫ LaCO3). Modeling of the data using Model VI and recently published stability constants for complexation of REE by humic acid well reproduced the experimental data, confirming the ability of Model VI to accurately determine REE speciation in natural waters. This modeling also confirms the reliability of recently published stability constants. This work shed more light not only on the competition between carbonates and HA for REE complexation but also on the reliability of WHAM 6 and Model VI for calculating the speciation of REE with organic matter in alkaline organic-rich water.Competition between humic acid (HA) and carbonates (Carb) for rare earth elements (REE) complexation.
Keywords: Rare earth elements; Humic acid; Carbonates; Binding; Speciation; Ultrafiltration;

This paper contributes to the comprehension of kinetic and equilibrium phenomena governing metal ion sorption on organic-matter-coated mineral particles. Sorption and desorption experiments were carried out with Eu ion and polyacrylic acid (PAA)-coated alumina colloids at pH 5 in 0.1 M NaClO4 as a function of the metal ion loading. Under these conditions, M interaction with the solid is governed by sorbed PAA (PAAads). The results were compared with spectroscopic data obtained by time-resolved laser-induced fluorescence spectroscopy (TRLFS) with Cm and Gd. The interaction between M and PAAads was characterized by a kinetically controlled process: after rapid metal adsorption within less than 1 min, the speciation of complexed M changed at the particle surface till an equilibrium was reached after about 4 days. At equilibrium, one part of complexed M was shown to be not exchangeable. This process was strongly dependent on the ligand-to-metal ratio. Two models were tested to explain the data. In model 1, the kinetically controlled process was described through successive kinetically controlled reactions that follow the rapid metal ion adsorption. In model 2, the organic layer was considered as a porous medium: the kinetic process was explained by the diffusion of M from the surface into the organic layer. Model 1 allowed a very good description of equilibrium and kinetic experimental data. Model 2 could describe the data at equilibrium but could not explain the kinetic data accurately. In spite of this disagreement, model 2 appeared more realistic considering the results of the TRLFS measurements.The question addressed in this study is to assess the effect of the adsorption of an organic polyelectrolyte onto a mineral phase on its complexation properties for metal ions.
Keywords: Ternary system; Adsorption; Polyacrylic acid; Eu; Cm; Time resolved laser induced fluorescence spectroscopy;

Visible polyaniline–latex particles 13 μm in diameter were used for obtaining a quantitative relationship between the adsorption force and the electroactivity at a platinum electrode. An optical cell equipped with wire electrodes was filled with the suspension in hydrochloric acid. When electrode potential was switched between the oxidized and the reduced domains, some adsorbed particles showed color change owing to the electroactivity. The numbers of electroactive and the inactive particles in the suspension were counted, including poly(N-vinylpyrrolidone) (PVP). The ratio of the numbers was proportional to the concentration of PVP, as it was in equilibrium. The adsorbed particles were desorbed mechanically by forced flow. The numbers of the desorbed particles did not decrease with an increase in the flow velocity until threshold values. The threshold value for the electroactive particle was 10 times larger than that for the inactive ones, corresponding to 10 times larger adsorption energy of the electroactive particles than of the inactive ones. The adsorption stress was evaluated from the removal of the electropolymerized polyaniline film from the electrode. Then the adsorption area of the particle was estimated.Some polyaniline latex particles were electroactive (color change) on the potential-controlled Pt electrode, and some were not.
Keywords: Polyaniline; Latex particles; Poly(N-vinylpyrrolidone); Adsorption force; Suspensions;

The influence of a first (anchoring) layer and film treatment on the structure and properties of polyelectrolyte multilayer (PEM) films obtained from polyallylamine hydrochloride (PAH) and polysodium 4-styrenesulfonate (PSS) was studied. Branched polyethyleneimine (PEI) was used as an anchoring layer. The film thickness was measured by ellipsometry. Complementary X-ray reflectometry and AFM experiments were performed to study the change in the interfacial roughness. We found that the thickness of the PEM films increased linearly with the number of layers and depended on the presence of an anchoring PEI layer. Thicker films were obtained for multilayers having PEI as the first layer comparing to films having the same number of layers but consisting of PAH/PSS only. We investigated the wettability of PEM surfaces using direct image analysis of the shape of sessile water drops. Periodic oscillations in contact angle were observed. PAH-terminated films were more hydrophobic than films with PSS as the outermost layer. The effect of long time conditioning of PEM films in solutions of various pH's or salt (NaCl) concentrations was also examined. Salt or base solutions induced modification in wetting properties of the polyelectrolyte multilayers but had a negligible effect on the film thickness.
Keywords: Polyelectrolyte multilayers; LbL technique; Ellipsometry; X-ray reflectometry; Wetting;

The structural examination of the complexes formed between humic acid and cationic surfactants has environmental implications. A humic acid (HA) dissolved in 0.1 M NaOH (5 g/L) was reacted with a cationic surfactant (hexadecyltrimethylammonium bromide or CTAB) at initial solution concentrations of 1, 5, 10, 20, 30, 40 and 50 mM. The HA precipitated at CTAB concentrations of 20, 30, and 50 mM but the complexes were soluble at 40 mM and below 20 mM. The charge neutralization between humic acid anions and CTAB micelles and the subsequent charge reversal due to hydrophobic interactions explain the behavior of the HA-CTAB complexes. The HA solution (5 g/L), reaction products (supernatants and precipitates), and pure cationic surfactant solutions were studied by the small-angle X-ray scattering (SAXS) technique in order to determine the structure of HA-CTAB complexes. The scattering intensity ( I ( q ) ) of various HA-CTAB systems were recorded over a range of scattering vectors ( q = 0.053 – 4.0   nm −1 ). HA forms networks in an alkaline solution with a characterization length of 7.8 nm or greater. The HA-CTAB precipitates and the 50-mM CTAB solution gave d 100 and d 110 reflections of a hexagonal structure. The hexagonal array of cylindrical CTAB micelles has a lattice parameter of 5.01 nm in pure solution, and the parameter decreases in the order: 4.96, 4.91, and 4.85 nm for the precipitates of HA-CTAB (50, 30, and 20 mM, respectively), indicating that the structure of CTAB micelles was disturbed by the addition of HA. The molecular properties and behavior of HA in solution were discussed.Humic acid acts as a polyvalent anion neutralizing the positive charges on CTAB micelles in a manner similar to the reaction between charged polymers and surfactants. At high CTAB concentration the hexagonal array structure of CTAB micelles was preserved, though deformed by the interaction, suggesting that there is no regular repetition of structural units in humic acid because such structural regularity would have caused the formation of new CTAB structures.
Keywords: Small-angle; X-ray scattering; Humic acid; Cationic surfactant;

Chitosan-N-poly(ethylene oxide) brush polymers for reduced nonspecific protein adsorption by Ye Zhou; Bo Liedberg; Natalija Gorochovceva; Ricardas Makuska; Andra Dedinaite; Per M. Claesson (62-71).
The possibility of using a novel comb polymer consisting of a chitosan backbone with grafted 44 units long poly(ethylene oxide) side chains for reducing nonspecific protein adsorption to gold surfaces functionalized by COOH-terminated thiols has been explored. The comb polymer was attached to the surface in three different ways: by solution adsorption, covalent coupling, and microcontact printing. The protein repellant properties were tested by monitoring the adsorption of bovine serum albumin and fibrinogen employing surface plasmon resonance and imaging null ellipsometry. It was found that a significant reduction in protein adsorption is achieved as the comb polymer layer is sufficiently dense. For solution adsorption this was achieved by adsorption from high pH solutions. On the other hand, the best performance of the microcontact printed surfaces was obtained when the stamp was inked either at low or at high pH. For a given comb polymer layer thickness/poly(ethylene oxide) density, significant differences in protein repellant properties were observed between the different preparation methods, and it is suggested that a reduction in the mobility of the comb polymer layer generated by covalent attachment favors a reduced protein adsorption.A comb polymer chitosan-N-PEO is prepared on COOH-functionalized gold thin films. The polymer coating is attached via electrostatic adsorption, covalent binding, and microcontact printing. Our results demonstrated that a reduced PEO chain mobility favors low levels of nonspecific protein binding.
Keywords: Comb polymer; Comb polyelectrolyte; Chitosan; Poly(ethylene oxides); Nonspecific binding; Adsorption; Microcontact printing; Surface plasmon resonance; Imaging null ellipsometry;

A homogeneous liquid phase reaction between barium chloride (BaCl2) and sodium sulphate (Na2SO4) was conducted in a narrow channel reactor to produce barium sulphate (BaSO4) precipitate. The effects of channel dimensions and channel residence times on crystal size, crystal size distribution, nucleation rates, crystal morphology and conversion of reactants were investigated at different levels of reactant supersaturation ratio. Our results indicate that the smallest particle sizes are favoured when supersaturation ratios and channel velocities are high. The minimum average particle diameter observed was approximately 0.2 μm in a channel of hydraulic diameter 0.5 mm and length 20 cm at an initial supersaturation ratio of 4483 (0.1 M), which correspond to conditions giving rise to the highest nucleation rates. It has also been observed that particle size depends on the conversion to product, the smallest particles being formed when conversion lies within the range of 30 to 40%. Conversions in excess of 60% have been reached but there is a detectable limiting effect with increased supersaturation and reduced residence times. Experiments conducted at similar levels of supersaturation under stirred tank conditions showed that particle size was consistently larger and particle size distribution was much broader than that achieved in the narrow channel reactor. Scanning electron microscopy (SEM) images of the crystals formed in the narrow channels show that spherical particles dominate in the smallest channels at high velocities whilst coarse, tabular crystals are obtained in the larger channels. Greater tendency to agglomerate is also observed at high supersaturation ratios, after one minute of reaction.Narrow channels have been shown to reduce mean particle size of barium sulphate to 0.2 μm where hydraulic channel diameter of 0.5 mm is used.
Keywords: Process intensification; Narrow channel reactor; Barium sulphate precipitation; Supersaturation; Particle size; Particle size distribution; Morphology;

It remains a challenge to measure dynamics in dense colloidal systems. Multiple scattering and low light-transmission rates often hinder measurements in such systems. One of the well-established techniques for overcoming the problem of multiple scattering is cross-correlation techniques such as 3D dynamic light scattering (3D-DLS). However, a high degree of multiple scattering, i.e., vanishing single-scattering contribution in the signal, limits the use of the 3D-DLS technique. We present another approach to measure turbid media by way of upgrading our flat-cell light-scattering instrument (FCLSI). This instrument was originally designed for static light-scattering (SLS) experiments and is similar to a Fraunhofer setup, which features a flat sample cell. The thickness of the flat sample cell can be varied from 13 μm to 5 mm. The small thickness increases the transmission, reduces multiple scattering to a negligible amount, and therefore enables the investigation of dense colloidal systems. We upgraded this instrument for DLS measurements by the installation of an optical single-mode fiber detector in the forward scattering regime. We present our instrumentation and subsequently test its limits using a concentration series of a turbid colloidal suspension. We compare the performances of our modified flat-cell light-scattering instrument with that of standard DLS and with that of 3D-DLS. We show that 3D-DLS and FCLSI only have a comparable performance if the length of the light path in the sample using the 3D-DLS is reduced to a minimum. Otherwise, the FCLSI has some advantage.To measure the dynamics of turbid systems is of great interest for fundamental research as well as industrial applications. We show the performance of a modified flat-cell light-scattering instrument.
Keywords: Turbid media; Multiple scattering; Dynamic light scattering; 3D cross correlation;

The pH-dependent charges of Hungarian soils have been studied via surface acid–base properties. The intrinsic stability constants of protonation and deprotonation processes, as well as the concentration of surface sites, have been determined by surface complexation modeling. The protonation and deprotonation constants have been nearly the same for most soils. There is a relation between the concentration of surface sites and composition, expect for the freshly deposited soils with high primary silicate content. The results show that the concentrations of silanol and aluminol sites are different for each soil, the intrinsic stability constants of protonation and deprotonation processes, however, are nearly the same within experimental error. This can only be explained if these stability constants are real thermodynamic equilibrium constants. The fact that these constants are nearly the same supports the conclusion that we succeeded in excluding all processes that would disturb the measurements. The parameters characteristic of the edge sites of the soils are of two types: (a) the parameters depending on the quality and composition of the soils, (i.e.), the concentration of surface sites; (b) the parameters depending on the thermodynamically well-defined acid–base processes, independent of soil composition.
Keywords: Acid–base properties; Soil; Soil acidity; Surface complexation;

Humidity-induced restructuring of the calcite surface and the effect of divalent heavy metals by Douglas B. Hausner; Richard J. Reeder; Daniel R. Strongin (101-110).
The composition and topography of calcite { 10 1 ¯ 4 } cleavage surfaces, with and without exposure to divalent metals, have been investigated as a function of relative humidity. Atomic force microscopy (AFM) was used to understand topographical changes on the calcite surface due to the presence of divalent metal and exposure to different humid environments. Ion scattering spectroscopy (ISS) was used to determine the composition of the near and outermost surface of the calcite after exposure to Cd and Pb and before exposure to the varying humidity conditions. In general, the extent of topographical changes observed on the calcite surface increased with the humidity level, though the initial step density of the cleaved calcite surface affects the extent of surface restructuring. Pretreatment of the calcite surface with aqueous divalent Pb prior to humidity exposure did not appear to alter the humidity-induced structural changes that occurred on the calcite surface. In contrast, calcite pretreated with divalent Cd showed little topographical change following exposure to high humidity. The results suggest that while Pb forms surface precipitates on the calcite surface, Cd exhibits a stronger interaction with the step edges of the calcite surface, which inhibits the ability of the calcite surface to restructure when exposed to a high relative humidity environment.Calcite surfaces exposed to humid environments exhibit surface restructuring as a function of humidity level, atomic step density, and exposure time. Pre-exposure to Cd2+ bearing solution has an inhibitory effect while Pb2+ does not show an effect.
Keywords: Calcite; Calcium carbonate; Surface restructuring; Cadmium; Lead; Humidity; Atomic force microscopy; Phase imaging;

Nozzle and liquid effects on the spray modes in nanoelectrospray by Mark D. Paine; Matthew S. Alexander; John P.W. Stark (111-123).
Unforced nanoelectrospray can exhibit a number of stable spray modes. These include low frequency pulsations, high frequency pulsations, and a steady cone-jet. Experiments are reported here on such pulsations that have been observed in various salt loaded solutions of ethylene glycol, triethylene glycol and water. The spray current was monitored with 1 μs time resolution to show that spray regime characteristics depend on nozzle diameter and liquid conductivity. The frequency of pulsations was found to increase with both increased liquid conductivity and decreasing nozzle diameter. The charge ejected during a pulse is lower for smaller nozzles spraying higher conductivity liquids. Water solutions were observed undergoing high frequency pulsations, with these pulsations often occurring in lower frequency bursts. The frequencies of water pulsations were as high as 635 kHz but the charge ejected by each pulsation was an order of magnitude lower than that observed in triethylene glycol. An unforced electrospray of water was also identified as being in the steady cone-jet mode with a higher degree of confidence than previously. The values for stable pulsation frequency and charge ejected observed in ethylene glycol lay between those of TEG and water.The oscillating meniscus of water undergoing stable but pulsating nanoelectrospray atomization. The pulsations are characterized in this work.
Keywords: Atomization; Nanoelectrospray; Electrospray; Pulsation; Nanospray; VMES;

Absorption and desorption of organic liquids in elastic superhydrophobic silica aerogels by A. Venkateswara Rao; Nagaraja D. Hegde; Hiroshi Hirashima (124-132).
The experimental results of the studies on the absorption and desorption of organic liquids in elastic superhydrophobic silica aerogels, are reported. The elastic superhydrophobic aerogels were prepared using methyltrimethoxysilane (MTMS) precursor by a two-step sol–gel process followed by supercritical drying. Monolithic superhydrophobic silica aerogels were used as the absorbents. In all, four alkanes, three aromatic compounds, four alcohols and three oils were used. The absorption property of the aerogel was quantified by the mass and moles of the organic liquid absorbed by unit mass of the aerogel. The superhydrophobic aerogels showed a very high uptake capacity and high rate of uptake. The desorption of solvents and oils was studied by maintaining the as-absorbed aerogel samples at various temperatures and weighing them at regular time intervals until all the absorbed liquid got totally desorbed. This was verified by measuring the weights of the aerogel samples before and after desorption. The transmission electron micrograph observations showed that the aerogel structure was not much affected by the solvent absorption, while the oil absorption led to the shrinkage resulting in a dense structure after the desorption. In all the cases, the aerogels retained hydrophobicity and could be re-used as absorbents.Monolithic superhydrophobic silica aerogels were used as the absorbents of organic liquids and oils. The absorption property of the aerogel was quantified by the mass and moles of the organic liquid absorbed by unit mass of the aerogel. The superhydrophobic aerogels showed a very high uptake capacity and high rate of uptake. The aerogel structure was not affected by the organic liquid absorption, while the oil absorption led to the shrinkage resulting in a dense structure after the desorption. The figure shows the desorption time of organic solvents as a function of vapor pressure.
Keywords: Oil spill clean-up; Elastic superhydrophobic aerogels; Porous materials; Absorption of organic liquids; Superhydrophobicity;

Study of reverse micelles of di-isobutylphenoxyethoxyethyldimethylbenzylammonium methacrylate in benzene by nuclear magnetic resonance spectroscopy by Saim M. Emin; Pavletta S. Denkova; Karolina I. Papazova; Ceco D. Dushkin; Eiki Adachi (133-141).
1H NMR spectroscopy was used to investigate the aggregation of the surfactant di-isobutylphenoxyethoxyethyldimethylbenzylammonium methacrylate (Hyamine-M) in benzene. Adding water makes swollen reverse micelles (microemulsion droplets). The droplets also contain cadmium ions and the sodium salt of the methacrylic acid. The critical micelle concentration of Hyamine-M was determined by NMR to be 3.95 mM under the current conditions. Two-dimensional NMR NOESY spectra were used to study the conformation of the surfactant in the micelle and the spatial localization of water and counterions. We found that the surfactant molecules are folded with both phenyl fragments oriented toward the micelle exterior and the oxyethylene and N―CH3 groups in the micelle core. The water molecules and counterions are distributed around the surfactant polar groups in the micelle interior and penetrate up to both aromatic rings. The investigated system can be further utilized as a microemulsion matrix for the synthesis of cadmium-containing semiconductor nanocrystals, eventually capped with a polymer shell, or of polymer nanoparticles. 1H NMR spectroscopy was used to determine the CMC in the system Hyamine-M/water/benzene. The 2D NOESY method was applied to investigate the possible conformations of the surfactant molecules in the reverse micelles and the spatial localization of the water molecules into the micelle core.
Keywords: NMR; 2D NOESY; CMC; Reverse micelles; Di-isobutylphenoxyethoxyethyldimethylbenzylammonium methacrylate; Hyamine-M; Polymer nanospheres;

In this work we present equilibrium and dynamic surface tension together with dilational elasticity data for dodecyltrimethylammonium bromide in the presence of λ-carrageenan, a sulfated polysaccharide extracted from algae. The critical aggregation concentration and (CAC) and critical micellar concentration CMC of the mixed system were determined and shown to have a direct influence on the elasticity modulus. The behavior of the adsorption kinetics was shown to be dependent on the surfactant to polyelectrolyte charge ratio or excess species in the bulk solution.In this work we present equilibrium and dynamic surface tension together with dilational elasticity data for DTAB/λ-carrageenan, a sulfated polysaccharide extracted from algae.
Keywords: Dodecyltrimethylammonium bromide; Carrageenan; Polyelectrolyte; Adsorption; Surface tension; Dilational elasticity;

Surfaces of a Wyoming SWy-2 sodium montmorillonite were modified using microwave radiation through intercalation with the cationic surfactants octadecyltrimethylammonium bromide, dimethyldioctadecylammonium bromide, and methyltrioctadecylammonium bromide by an ion exchange mechanism. Changes in the surfaces and structure were characterized using X-ray diffraction (XRD), thermal analysis (TG) and infrared (IR) spectroscopy. Different configurations of surfactants within montmorillonite interlayer are proposed based on d ( 001 ) basal spacings. A range of surfactant molecular environments within the surface-modified montmorillonite are proposed based upon their thermal decomposition. IR spectroscopy using a smart endurance single bounce diamond attenuated total reflection (ATR) cell has been used to study the changes in the spectra of CH asymmetric and symmetric stretching modes of the surfactants to provide more information of the surfactant molecular configurations.Surfaces of a Wyoming SWy-2 sodium montmorillonite were modified through intercalation using microwave radiation and adsorption of the cationic surfactants octadecyltrimethylammonium bromide, dimethyldioctadecylammonium bromide, and methyltrioctadecylammonium bromide. Different configurations of surfactants within montmorillonite interlayer are proposed based on d ( 001 ) basal spacings.
Keywords: Surfactant; Organoclay; Montmorillonite; Adsorption; Surface modification;

A finite element implementation of the transient nonlinear Nernst–Planck–Poisson (NPP) and Nernst–Planck–Poisson–modified Stern (NPPMS) models is presented. The NPPMS model uses multipoint constraints to account for finite ion size, resulting in realistic ion concentrations even at high surface potential. The Poisson–Boltzmann equation is used to provide a limited check of the transient models for low surface potential and dilute bulk solutions. The effects of the surface potential and bulk molarity on the electric potential and ion concentrations as functions of space and time are studied. The ability of the models to predict realistic energy storage capacity is investigated. The predicted energy is much more sensitive to surface potential than to bulk solution molarity.
Keywords: Electric double layer; Nernst–Planck–Poisson; Finite element analysis;

Transport of ions through the oil phase of W1/O/W2 double emulsions by Jing Cheng; Jian-Feng Chen; Min Zhao; Qing Luo; Li-Xiong Wen; Kyriakos D. Papadopoulos (175-182).
Using a capillary video microscopy technique, the ion transport at liquid–liquid interfaces and through a surfactant-containing emulsion liquid membrane was visually studied by preparing a double emulsion globule within the confined space of a thin-walled, transparent, cylindrical microtube. NaCl and AgNO3 were selected as the model reactants and were prepared to form a NaCl/AgNO3 pair across the oil film. By observing and measuring the formed AgCl deposition, it was found that both Cl and Ag+ could transport through a thick oil film and Ag+ was transported faster than Cl. Interestingly, the ion transport was significantly retarded when the oil film became extremely thin ( < 1   μm ). The results suggested that the transport of ions mainly depends on the “reverse micelle transport” mechanism, in which reverse micelles with entrapped ions and water molecules can be formed in a thick oil film and their construction will get impeded if the oil film becomes extremely thin, leading to different ion transport rates in these two cases. The direction of ion transport depends on the direction of the osmotic pressure gradient across the oil film and the ion transport is independent of the oil film thickness in the investigated thick range. Ions with smaller Pauling radii are more easily entrapped into the formed reverse micelles and therefore will be transported faster through the oil film than bigger ions. Oil-soluble surfactants facilitate ion transport; however, too much surfactant in the oil film will slow down the ion migration. In addition, this study showed no support for the “molecular diffusion” mechanism of ion transport through oils.Ion transport through the oil film in double emulsions mainly depends on the “reverse micelle transport.” The transport rate is determined by the ion size, oil film thickness and surfactant concentration, etc.
Keywords: Ion transport; Visualization; Double emulsion; Reverse micelle;

Imaging of the concentration profiles of the diffusants during molecular adsorption on and desorption from porous media is developing to become an important, very specific tool of monitoring the structure of these media. With the present study we refer to the remarkable phenomenon that even in the case of anisotropic porous media the concentration profiles recorded under desorption may attain isotropic patterns, irrespective of the fact that desorption is limited by anisotropic diffusion. The presentation is based on both dynamic Monte Carlo simulations and analytical considerations.Anisotropic porous media desorption concentration profiles may attain isotropic patterns, irrespective of the fact that desorption is limited by anisotropic diffusion. This results from Monte Carlo simulations and analytical considerations.
Keywords: Anisotropic diffusion; Desorption; Dynamic Monte Carlo simulation; Analytical consideration; Concentration profiles;

The Helmholtz–Smoluchowski (HS) equation is widely used to determine the apparent zeta potential of porous materials using the streaming potential method. We present a model able to correct this apparent zeta potential of granular media of the influence of the Dukhin and Reynolds numbers. The Dukhin number represents the ratio between the surface conductivity (mainly occurring in the Stern layer) and the pore water conductivity. The Reynolds number represents the ratio between inertial and viscous forces in the Navier–Stokes equation. We show here that the HS equation can lead to serious errors if it is used to predict the dependence of zeta potential on flow in the inertial laminar flow regime without taking into account these corrections. For indifferent 1:1 electrolytes (such as sodium chloride), we derived two simple scaling laws for the dependence of the streaming potential coupling coefficient (or the apparent zeta potential) on the Dukhin and Reynolds numbers. Our model is compared with a new set of experimental data obtained on glass bead packs saturated with NaCl solutions at different salinities and pH. We find fairly good agreement between the model and these experimental data.In this paper, we model the influence of the Dukhin and Reynolds numbers upon the apparent zeta potential of granular media. (a) and (b) are comparisons between the model and the experimental data.
Keywords: Streaming potential; Zeta potential; Dukhin number; Reynolds number; Surface conductivity; Electrical conductivity; Streaming current; Electrokinetic; Helmholtz–Smoluchowski equation;

Electrical oscillation at a water/octanol interface in a hydrophobic container by Takehito Ogawa; Hiroshi Shimazaki; Satoka Aoyagi; Kiyotaka Sakai (195-197).
The electrical potential oscillation at and the shape of the water/octanol interface were investigated using hydrophobic fluoroplastic containers. The interfacial potential between a water solution containing 1.5 mM sodium dodecyl sulfate (SDS) and an octanol solution containing 5 mM tetrabutylammonium chloride oscillated with an amplitude of 50–100 mV. The potential oscillation was also observed using a transparent fluoroplastic tube. The water/octanol interface shape was unchanged and no interfacial flow was observed during the oscillation. The interface shape was convex toward the octanol phase for 1.5 mM SDS, meaning that SDS adsorption to the wall was suppressed by the hydrophobic container. Therefore, the octanol system in a hydrophobic container enabled us to elucidate the electrical oscillation without any influence from the wall effect.Electrical oscillation in a two-phase system using octanol and sodium dodecyl sulfate in a fluoroplastic container was evaluated to study the mechanism of electrical oscillation.
Keywords: Electrical oscillation; Octanol; Surfactant; Hydrophobic container;

Chemical synthesis and crystallization of the dipeptide AcPheIleNH2 in TTAB/heptane/octanol reversed micelles by A.I. Dias; A.S. Feliciano; J.M.S. Cabral; D.M.F. Prazeres (198-201).
The chemical synthesis of the dipeptide acetyl phenyl isoleucinamide (AcPheIleNH2) in tetradecyl trimethyl ammonium bromide (TTAB)/ heptane/octanol/carbonate buffer reversed micelles is described. The co-existence of the surfactant bounded minute water pools within the bulk organic solvent enables the simultaneous solubilization of the polar (IleNH2) and apolar (AcPheOEt) substrates, thus enabling the synthesis to take place at the micellar interface. The synthesis was favored by increasing the micellar interface via an increase in water content and surfactant concentration. The best dipeptide yield (87%) was obtained at 32 °C, with the largest concentrations of TTAB (200 mM) and water (1100 mM) tested. The low solubility of the dipeptide in the micellar media further led to the formation and growth of needle-like crystals during synthesis, thus enabling the removal of product from solution.The chemical synthesis and simultaneous crystallization of the dipeptide AcPheIleNH2 in reversed micelles is described.
Keywords: Reversed micelles; Chemical synthesis; Dipeptide; Crystallization;

Solubilization kinetics of soluble oils by an ionic surfactant by P. Neogi; James J. Munden (202-203).
Previously available data on solubilization kinetics of two oils in a micellar solution of sodium dodecyl sulfate, have been plotted with the data for one more oil provided here. These rates show that they reach saturation values with increasing micellar concentrations. These saturation values are then shown to be linearly dependent on the solubilities of oil, in keeping with the theory that the mechanism for solubilization of soluble oils by an ionic surfactant is chiefly molecular dissolution of the oil followed by a quick uptake by the micelles.Solubilization of oil starts with the dissolution of oil in water followed by a quick uptake of oil by micelles.
Keywords: Solubilization kinetics; Sodium dodecyl sulfate; Oil solubility;

Incorporation of platinum nanoparticles in ordered mesoporous carbon by Kjell Wikander; Ana B. Hungria; Paul A. Midgley; Anders E.C. Palmqvist; Krister Holmberg; John M. Thomas (204-208).
Platinum nanoparticles were incorporated within the pore system of ordered mesoporous carbon (OMC) by impregnating the carbon with a water-in-oil (w/o) microemulsion containing dissolved platinum salt followed by reduction of the platinum ions in situ inside the carbon pore system. The procedure provides preparation of metallic nanoparticles from hydrophilic precursors inside the hydrophobic carbon support structure with simultaneous control of the maximum metal particle size. Electron tomography was used to verify the presence of platinum nanoparticles inside the carbon material.
Keywords: Platinum; Nanoparticles; Microemulsion; Mesoporous; Carbon; Electron tomography;