Journal of Colloid And Interface Science (v.314, #2)

Adsorption of short heteropolymers in slitlike pores by M. Borówko; W. Rżysko; S. Sokołowski; T. Staszewski (349-357).
Adsorption of short linear heteropolymers in slitlike pores is studied using the density functional theory and Monte Carlo simulations. The molecules are assumed to be freely jointed tangent hard spheres. The segments have different affinity with regard to the walls. Each molecule contains one surface-binding segment that interacts with the walls via Lennard–Jones ( 3 , 9 ) potential and a number of segments interacting with surfaces via the hard-wall potentials. A position of the surface-binding segment in the chain can be arbitrarily chosen. We have studied the influence of the pore width, the chain length and the chemical structure of molecules on adsorption and the microscopic structure of the confined fluid. The theoretical predictions are compared with Monte Carlo simulations carried out for different ‘isomeric’ pentamers.
Keywords: Adsorption; Polymers; Slitlike pores; Density functional theory; Monte Carlo simuliations;

The layer-by-layer deposition of two polyelectrolytes, quaternized poly(dimethylaminoethyl methacrylate chloride) (MADQUAT) and poly(acrylic acid) (PAA) on a silica substrate was investigated using optical reflectometry, as a function of pH (pH 4, 5.5 and 9), ionic strength (10−3 to 10−1 M) and type of salt. Attention was given to the successive deposited weights and to the corresponding deposited charge densities within the ten first deposited layers. Results show a change of growth regime between an early stage where the substrate had a dominating influence in the build-up and a second stage where the polymer uptake was ruled essentially by polymer–polymer interactions. The pH was seen to influence the growth via the charge densities of silica (first stage) and PAA (first and second stages). The increase of NaCl concentration induced an increase of the film weight between 10−3 and 10−2 M, but the trend was more sophisticated between 10−2 and 10−1 M where the polymer uptake increased in the first stage of the growth and decreased in subsequent layers. The film weight increased in accordance with the rank of ions in the Hofmeister series. AFM images revealed a heterogeneous film morphology with bumps and valleys, which was explained by a growth mechanism made of the successive formation and growth of polymer complexes.Morphology of five MADQUAT/PAA bilayers deposited onto silica substrate (AFM image).
Keywords: Polyelectrolyte multilayers; Layer-by-layer adsorption; pH influence; Ionic strength influence; Poly(acrylic acid); Poly(dimethylaminoethyl methacrylate chloride);

Novel three-stage kinetic model for aqueous benzene adsorption on activated carbon by Jae-Woo Choi; Nag-Choul Choi; Soon-Jae Lee; Dong-Ju Kim (367-372).
We propose a novel kinetic model for adsorption of aqueous benzene onto both granular activated carbon (GAC) and powdered activated carbon (PAC). The model is based on mass conservation of benzene coupled with three-stage adsorption: (1) the first portion for an instantaneous stage or external surface adsorption, (2) the second portion for a gradual stage with rate-limiting intraparticle diffusion, and (3) the third portion for a constant stage in which the aqueous phase no longer interacts with activated carbon. An analytical solution of the kinetic model was validated with the kinetic data obtained from aqueous benzene adsorption onto GAC and PAC in batch experiments with two different solution concentrations ( C 0 = 300   mg L −1 , 600 mg L−1). Experimental results revealed that benzene adsorption for the two concentrations followed three distinct stages for PAC but two stages for GAC. The analytical solution could successfully describe the kinetic adsorption of aqueous benzene in the batch reaction system, showing a fast instantaneous adsorption followed by a slow rate-limiting adsorption and a final long constant adsorption. Use of the two-stage model gave incorrect values of adsorption coefficients in the analytical solution due to inability to describe the third stage.A novel kinetic model is proposed to describe adsorption of aqueous benzene onto activated carbon, showing three-stage adsorption: (1) the first portion for the instantaneous stage, (2) the second portion for the gradual stage, and (3) the third portion for the constant stage.
Keywords: Adsorption; Aqueous benzene; Granular activated carbon; Powdered activated carbon; Three-stage kinetic model;

A study of the surface properties of cotton fibers by inverse gas chromatography by Narjès Rjiba; Michel Nardin; Jean-Yves Dréan; Richard Frydrych (373-380).
In the present study, the potential relationships between the microstructure and the surface properties of different cotton fibers are analyzed by inverse gas chromatography (IGC) at infinite dilution. By measuring the retention time of polar and nonpolar gaseous probes into a column containing the fibers, surface characteristics of these fibers, in particular the dispersive component of their surface energy and their surface morphological index, were determined. It is clearly shown that the presence of natural waxes on cotton fibers plays a major role on their thermodynamic surface properties, affecting the surface energy and the acid–base character as well as the morphological aspects of such fibers. Finally, it appeared that IGC is a well appropriate method for the evaluation of the surface characteristics of cotton fibers.
Keywords: Inverse gas chromatography; Surface energy; Index of morphology; Cotton fiber; Cellulose; Extracted cotton fiber;

pH-responsive behavior of selectively quaternized diblock copolymers adsorbed at the silica/aqueous solution interface by Kenichi Sakai; Emelyn G. Smith; Grant B. Webber; Murray Baker; Erica J. Wanless; Vural Bütün; Steven P. Armes; Simon Biggs (381-388).
The desorption and subsequent pH-responsive behavior of selectively quaternized poly(2-(dimethylamino)ethyl methacrylate)-block-poly(2-(diethylamino)ethyl methacrylate) (PDMA–PDEA) films at the silica/aqueous solution interface has been characterized. The copolymer films were prepared at pH 9, where micelle-like surface aggregates are spontaneously formed on silica. The subsequent rinse with a copolymer-free electrolyte solution adjusted to pH 9 causes partial desorption of the weakly or non-quaternized copolymers, but negligible desorption for the highly quaternized copolymers. Further rinsing with a pH 4 electrolyte solution results in additional desorption and extension (swelling) of the remaining adsorbed copolymer film normal to the interface. This pH-responsive behavior is reversible for two pH cycles (9–4–9–4) as monitored by both quartz crystal microbalance with dissipation monitoring (QCM-D) and also ζ potential measurements. The magnitude of the pH-responsive behavior depends on the mean degree of quaternization of the PDMA block. Moreover, a combination of contact angle data, ζ potential measurements and in situ atomic force microscopy (AFM) studies indicates that the pH-responsive behavior is influenced not only by the number of cationic binding sites on the adsorbed copolymer chains but also by the adsorbed layer structure.The pH-responsive behavior of quaternized diblock copolymers adsorbed on silica has been characterized on the basis of the adsorbed amount, contact angle, ζ potential and in situ AFM data.
Keywords: pH-responsive diblock copolymer; Adsorption; Desorption; Quaternization;

Synthetic chrysotile nanocrystals as a reference standard to investigate surface-induced serum albumin structural modifications by Piera Sabatino; Luigi Casella; Alessandro Granata; Michele Iafisco; Isidoro Giorgio Lesci; Enrico Monzani; Norberto Roveri (389-397).
Geoinspired synthetic chrysotile, which represents an ideal asbestos reference standard, has been utilized to investigate homomolecular exchange of bovine serum albumin (BSA), the major plasma protein, between the adsorbed and dissolved state at the interface between asbestos fibers and biological medium. FTIR spectroscopy has been used to quantify BSA structural modifications due to surface adhesion on chrysotile fibers as a function of the surface coating extent. Circular dichroism spectroscopy has been used to investigate the adsorption/desorption equilibrium through analysis of the BSA structural perturbations after protein desorption from chrysotile surface. Data results show clearly that in the solid state BSA modifications are driven by surface interaction with the substrate, following a bimodal adsorption evidenced by two different binding constants. On the other hand, BSA desorbed in solution is able to rearrange, in the lack of substrate, although keeping irreversible modifications with respect to the native species. The lack of regaining its native structure certainly affects albumin interaction with biological environment. The present investigation on the stoichiometric synthetic geoinspired chrysotile nanocrystals is the first approach toward a deeper attempt to use standard synthetic chrysotile reference samples in mimicking the behavior of asbestos fibers and allows to better understand their interaction with a biological environment.Synthetic stoichiometric chrysotile nanofibers with constant structure and morphology have been first used as an ideal reference standard to define adsorption/desorption equilibrium of BSA. Irreversible protein unfolding has been quantified in the solid state and in the surnatant solutions as a function of the coating extent.
Keywords: Solid–liquid interface; Surface adsorption/desorption; Protein folding/unfolding; Synthetic chrysotile; Bovine serum albumin;

We used an oblique impinging jet (OIJ) cell to determine the initial deposition rates of model microcapsules at bare and modified by multilayer polyelectrolyte (PE) film mica surfaces. The transport conditions in the cell were quantitatively established by studying the kinetics of deposition of negatively charged latex at mica surfaces converted to positively charged by adsorption of (3-aminoprolyl)triethoxysilane. The dependence of reduced particle flux on the Reynolds number of the flow in the OIJ cell was determined by a direct counting of particles deposited on the mica surface. The results are described in terms of convective-diffusion theory taking into account hydrodynamic, dispersive, and electrostatic interactions, between the charged particles/capsules and the mica plate. In this way, transport conditions in the cell were characterized and they were used to interpret the results concerning the deposition of microcapsules with PE shells of various thickness obtained by layer-by-layer polyelectrolyte adsorption on colloidal cores. We demonstrated that the initial deposition rate of capsules is governed by the charge of the solid/liquid interface and the outermost layer of the capsule shell, and is largely independent of the thickness of the capsule shell or the number of PE layers at the mica surface. The deposition rates were in good agreement with theoretical predictions derived from the convective-diffusion theory.
Keywords: Deposition; Microcapsules; Polyelectrolyte; Layer-by-layer; Adsorption;

Water purification is of extreme importance worldwide. p-Nitrophenol was used as a test chemical to design and test an organoclay for the removal of p-nitrophenol from an aqueous solution. Synthesis of the organoclay with methyltrioctadecylammonium bromide [CH3(CH2)17]3NBr(CH3) labeled as MTOAB results in multiple expansions of the montmorillonite clay from 1.24 nm to a maximum of 5.20 nm as is evidenced by the XRD patterns. Thermal analysis shows strong bonding of the surfactant to the clay siloxane layers and the interaction of the p-nitrophenol with the clay surfaces. It is proposed that the p-nitrophenol penetrates the siloxane layer of the clay and bonds through the ditrigonal space of the siloxane hexagonal units to the inner OH units. Such a concept is supported by the observation of an additional infrared band at 3652 cm−1 for the organoclay. Shifts in the p-nitrophenol OH stretching vibrations mean a strong interaction of the p-nitrophenol molecule. Significant changes in the siloxane stretching bands are also observed.The mechanism of adsorption of p-nitrophenol on both nontreated montmorillonite and surfactant intercalated montmorillonite was studied by X-ray diffraction, thermogravimetry, and infrared spectroscopy. On the untreated and low CEC intercalated montmorillonite the p-nitrophenol adsorbed on the cation hydration sphere. At high CEC values the p-nitrophenol replaced the surfactant cation in the interlayer and bonded directly to the siloxane surface.
Keywords: Montmorillonite; Organoclay; Surfactant; Differential thermal analysis; Thermogravimetric analysis; X-ray diffraction; Infrared spectroscopy;

The adsorption of nitrogen in a collection of spheres that touch or merge in a sintering-like manner is modeled using a Derjaguin–Broeckhof–de Boer approach. The proposed model accounts for both positive curvature effects and for capillary condensation at the contact between two spheres. A methodology is proposed to fit the P / P 0 > 0.4 adsorption region with the coordination number of the spheres as the only adjustable parameter. The use of the model is illustrated on a series of silica aerogels. The suitability of various standard isotherms needed for the modeling is also discussed.
Keywords: Nitrogen adsorption; Particulate solids; Capillary condensation;

Adsorption of water on three-dimensional pillared-layer metal organic frameworks by Atsushi Kondo; Takamichi Daimaru; Hiroshi Noguchi; Tomonori Ohba; Katsumi Kaneko; Hirofumi Kanoh (422-426).
We showed water adsorption isotherms at 303 K on water-resistant three-dimensional (3-D) pillared-layer metal organic frameworks (MOFs) with 1-D semi-rectangular pores, of which size depends on the length of ligand. The shapes of all three adsorption isotherms are type I by IUPAC classification showing strong water–MOFs interaction. The adsorbed amount of water molecules on the hydrophilic site of carboxylic group in 2-D sheets coincided with the crystal water amount. The adsorption on the hydrophilic sites occurs at similar relative pressure even if the used ligand is different.We showed water adsorption isotherms at 303 K on water-resistant three-dimensional pillared-layer metal organic frameworks (MOFs) with 1-D semi-rectangular pores, of which size depends on the length of ligand.
Keywords: Water adsorption; Metal organic framework; Hydrophilic site; Ligand;

Mechanism of removal of arsenic by bead cellulose loaded with iron oxyhydroxide (β-FeOOH): EXAFS study by Xuejun Guo; Yonghua Du; Fuhua Chen; Hung-Suck Park; Yaning Xie (427-433).
Bead cellulose loaded with iron oxyhydroxide (BCF) with 47 mass% Fe content was prepared and was successfully applied to the elimination of arsenic from aqueous solutions. A clearer understanding of the arsenic removal mechanism will provide accurate prediction of the arsenic adsorptive properties of the new adsorbent. To study the mechanism of the adsorption process, we measured the extended X-ray absorption fine structure (EXAFS) spectra of arsenite and arsenate sorbed onto the adsorbent with different surface coverages. Both arsenite and arsenate were strongly and specifically adsorbed by akaganéite adsorptive centers on BCF by an inner-sphere mechanism. There was no change in oxidation state following interaction between the arsenic species and the BCF surface. The dominant complex of arsenic species adsorbed on akaganéite was bidentate binuclear corner-sharing (2C) between As(V) tetrahedra (or As(III) pyramids) and adjacent edge-sharing FeO6 octahedra. On the basis of the results from EXAFS spectra, the adsorptive characteristics of arsenic, such as the effects of pH and competing anions, were satisfactorily interpreted.As(V) sorbed onto iron phase of BCF adsorbent: bidentate–binuclear corner-sharing (2C).
Keywords: Adsorption; EXAFS; Iron oxyhydroxide; Bead cellulose;

Evaluation of molecular mechanics calculated binding energies for isolated and monolayer organic molecules on graphite by Thomas R. Rybolt; Christina E. Wells; Charles R. Sisson; Claire B. Black; Katherine A. Ziegler (434-445).
The calculated molecule–surface binding energy, E cal ∗ , for physical adsorption was determined using molecular mechanics MM2 parameters for a model graphite surface and various organic molecules. The results for E cal ∗ were compared to published experimental binding energy values, E ∗ , from gas chromatography (GC) or thermal desorption (TD). The binding energies from GC were for isolated molecules in the Henry's law region of adsorption, and the binding energies from TD were for molecules in monolayer coverage on a highly oriented pyrolytic graphite (HOPG). A simple desorption model was used to allow the calculation of monolayer coverage to include both molecule–surface and molecule–molecule interactions and then the results were compared to experimental values. For the 14 TD organic adsorbates (polyaromatic hydrocarbons, alcohols, benzene, substituted benzenes, methane, chloroalkanes, N , N -dimethylformamide, and C60 Buckyball), the experimental versus calculated binding energies were E ∗ = 1.1193 E cal ∗ and r 2 = 0.967 . The GC E ∗ values were also well correlated by calculated E cal ∗ values for a set of 11 benzene and methyl substituted benzenes and for another set of 10 alkanes and haloalkanes. The TD E cal ∗ mechanics computation provides a useful comparison to the one for GC data since adsorbate–adsorbate interactions as well as adsorbate–surface must be considered.Molecule–graphite binding energies calculated from molecular mechanics, based on a monolayer model, E cal ML ∗ , predict experiment binding energies obtained from thermal desorption, E avg ∗ .
Keywords: Adsorption; Gas–solid interaction energy; Molecular mechanics; Binding energy; Adsorption energy; Adsorption; Thermal desorption;

Polymer brushes in nanopores surrounded by silicon-supported tris(trimethylsiloxy)silyl monolayers by Voravee P. Hoven; Mayuree Srinanthakul; Yasuhiko Iwasaki; Ryoko Iwata; Suda Kiatkamjornwong (446-459).
A chemically grafted tris(trimethylsiloxy)silyl (tris(TMS)) monolayer on a silicon oxide substrate was used as a template for creating nanoclusters of polymer brushes. Polymer brushes were synthesized by surface-initiated polymerization of 2-methacryloyloxyethyl phosphorylcholine (MPC) and tert-butyl methacrylate (t-BMA) via atom transfer radical polymerization (ATRP) from α-bromoester groups tethered to the residual silanol groups on the silicon surface after generating a range of tris(TMS) coverage. CuBr/bpy and CuBr/PMDETA were used as the catalytic system for PMPC and Pt-BMA synthesis, respectively. The percentage of tris(TMS) coverage significantly influenced the thickness and morphology of the polymer brushes. Protrusions representing self-aggregation of PMPC brushes in nanopores as visualized by AFM analysis evidently suggested that PMPC brushes were distributed nanoscopically on the surface. The protrusion size and surface roughness corresponded quite well with the graft density of PMPC brushes. The fact that Pt-BMA brushes grown from nanopores were almost featureless implies that self-aggregation of PMPC brushes is truly a consequence of phase incompatibility between hydrophilic PMPC brushes and hydrophobic tris(TMS). The anti-fouling characteristic of PMPC brushes, inferred from plasma protein adsorption, was subsequently varied by controlling the surface coverage ratio between PMPC brushes and tris(TMS).
Keywords: Polymer brush; Phospholipid polymer; Surface-initiated polymerization; Atom transfer radical polymerization; Nanoscale template;

Derivatizing weak polyelectrolytes—Solution properties, self-aggregation, and association with anionic surfaces of hydrophobically modified poly(ethylene imine) by Peter C. Griffiths; Alison Paul; Ian A. Fallis; Champa Wellappili; Damien M. Murphy; Robert Jenkins; Sarah J. Waters; Renuka Nilmini; Richard K. Heenan; Stephen M. King (460-469).
The physical properties of weak polyelectrolytes may be tailored via hydrophobic modification to exhibit useful properties under appropriate pH and ionic strength conditions as a consequence of the often inherently competing effects of electrostatics and hydrophobicity. Pulsed-gradient spin-echo NMR (PGSE-NMR), electron paramagnetic resonance (EPR), small-angle neutron scattering (SANS) surface tension, fluorescence, and pH titration have been used to examine the solution conformation and aggregation behavior of a series of hydrophobically modified hyperbranched poly(ethylene imine) (PEI) polymers in aqueous solution, and their interaction with sodium dodecylsulfate (SDS). PGSE-NMR gave a particularly insightful picture of the apparent molecular weight distribution. The presence of the hydrophobes led to a lower effective charge on the polymer at any given pH, compared to the (parent) nonmodified samples. Analysis of the SANS data showed that the propensity to form highly elliptical or rod-like aggregates at higher pHs, reflecting both the changes in protonation behavior induced by the hydrophobic modification and an hydrophobic interaction, but that these structures were disrupted with decreasing pH (increasing charge). The parent samples were not surface active yet the hydrophobically modified samples show pronounced surface activity and the presence of small hydrophobic domains. The surface activity increased with an increase in the degree of modification. On addition of SDS, the onset of the formation of polymer/surfactant complexes was insensitive to the degree of modification with the resultant PEI/SDS complexes resembling the size and shape of simple SDS micelles. Indeed, the presence of the SDS effectively nullifies the effects of the hydrophobe. Hydrophobic modification is therefore a viable option to tailor pH dependent properties, whose effects may be removed by the presence of surfactant.The presence of the hydrophobic groups on branched PEI with molecular weight 25,000 g mol−1 rendered it surface active and led to the formation of hydrophobic domains. With decreasing pH, the rod-like aggregates beak-up into smaller, more elliptical units.
Keywords: Weak polyelectrolyte; Poly(ethylene imine); Hydrophobically modified polymer; Solution conformation; pH behavior; Radius of gyration; Neutron scattering; Diffusion coefficient distribution; Inverse Laplace transform;

Micelles formed by self-assembling of polylactide/poly(ethylene glycol) block copolymers in aqueous solutions by Liu Yang; Zhenxian Zhao; Jia Wei; Abdelslam El Ghzaoui; Suming Li (470-477).
Copolymers of polylactide (PLA) and poly(ethylene glycol) (PEG) were synthesized by ring-opening polymerization of l- or d-lactide in the presence of mono- or dihydroxyl PEG using nontoxic zinc lactate as catalyst. The resulting diblock and triblock copolymers were characterized by various analytical techniques such as SEC, 1H NMR, XRD, and DSC. Bioresorbable micelles were prepared from aqueous solutions of the various copolymers without using any organic solvent. The mixed micellar solutions containing both L-PLA/PEG and D-PLA/PEG copolymers appeared more stable than the separate solutions according to critical micellar concentration (CMC) results, which could be assigned to stronger interactions between L-PLA and D-PLA blocks. The properties of the polymeric micelles strongly depend on the chain structure and composition of the copolymers. CMC values in the presence of salt and at 37 °C suggested that the micelles could exhibit good stability in vivo. Thermodynamic parameters calculated from the dependence of CMC on temperature indicate that the micellization process is spontaneous and driven by entropy gain. Dynamic light scattering (DLS) measurements showed one or two populations of micelles for dilute and concentrated solutions, the micelle size decreasing upon dilution. TEM confirmed the presence of micelles, but the size estimated from TEM was smaller than that from DLS due to the dehydration and shrinkage during drying.Triblock copolymers of polylactide (PLA) and poly(ethylene glycol) (PEG) were synthesized by ring-opening polymerization of l- or d-lactide in the presence of dihydroxyl PEG using nontoxic zinc lactate as catalyst. Diblock copolymers were obtained similarly by using mono-hydroxyl PEG.
Keywords: Poly(l-lactide); Poly(d-lactide); Stereocomplexation; Poly(ethylene glycol); Critical micellar concentration;

Complexation of DNA with cationic gemini surfactant in aqueous solution by Xiaofang Zhao; Yazhuo Shang; Honglai Liu; Ying Hu (478-483).
Interactions between DNA and the cationic gemini surfactant trimethylene-1,3-bis(dodecyldimethylammonium bromide) (12-3-12) in aqueous solution have been investigated by UV–vis transmittance, zeta potential, and fluorescence emission spectrum. Complexes of DNA and gemini surfactant are observed in which the negative charges of DNA are neutralized by cationic surfactants effectively. The DNA-induced micelle-like structure of the surfactant due to the electrostatic and hydrophobic interactions is determined by the fluorescence spectrum of pyrene. It is found that the critical aggregation concentration (CAC) for DNA/12-3-12 complexes depends little on the addition of sodium bromide (NaBr) because of the counterbalance salt effect. However, at high surfactant concentration, NaBr facilitates the formation of larger DNA/surfactant aggregates. Displacement of ethidium bromide (EB) by surfactant evidently illustrates the strong cooperative binding between surfactant and DNA. In contrast to that in the absence of surfactant, the added NaBr at high surfactant concentration influences not only the binding of surfactant with DNA, but also the stability of DNA/EB complex.The added NaBr at high surfactant concentration not only influences the binding of surfactant with DNA, but also the stability of DNA/EB complex.
Keywords: DNA; Gemini surfactant; Electrostatic interaction; Hydrophobic interaction; Fluorescence;

Buffer capacity of humic acid: Thermodynamic approach by Jonas Pertusatti; Alexandre G.S. Prado (484-489).
Commercial humic acid was dialyzed and characterized by infrared, UV/vis spectroscopy, 13C NMR spectrometry, thermogravimetry, and elemental analysis. The dialyzed humic acid was titrated with HNO3 and NaOH in order to obtain the buffer capacity value (β). The humic acid presented buffer behavior by base and acid addition, and moreover, an excellent buffer capacity by addition of NaOH. Humic acid showed buffer action between pH 5.5 and 8.0, and a maximum buffer capacity at pH 6.0. The same study was followed calorimetrically to determinate the enthalpy of interaction between H+/OH and buffer, which resulted in a maximum enthalpy of −38.49 kJ mol−1 at pH 6.0. This value suggests that the buffer activity is based on chemisorption of proton and hydroxyl.Buffer capacity variation (○) and the heat (■) versus pH range.
Keywords: Humic acid; Thermodynamic data; Buffer capacity;

Is trace metal release in wetland soils controlled by organic matter mobility or Fe-oxyhydroxides reduction? by Malgorzata Grybos; Mélanie Davranche; Gérard Gruau; Patrice Petitjean (490-501).
Aerobic and anaerobic incubation experiments on a wetland soil samples were used to assess the respective roles of organic matter (OM) release, Fe-oxyhydroxides reduction and redox/speciation changes on trace metal mobility during soil reduction. Significant amounts of Cu, Cr, Co, Ni, Pb, U, Th and Rare Earth Elements (REE) were released during anaerobic incubation, and were accompanied by strong Fe(II) and dissolved organic matter (DOM) release. Aerobic incubation at pH 7 also resulted in significant trace metal and DOM release, suggesting that Fe-oxyhydroxide reduction is not the sole mechanism controlling trace metal mobility during soil reduction. Using these results and redox/speciation modeling, four types of trace metal behavior were identified: (i) metals bound to organic matter (OM) and released by DOM release (REE); (ii) metals bound to both OM and Fe-oxyhydroxides, and released by the combined effect of DOM release and Fe(III) reduction (Pb and Ni); (iii) metals bound solely to soil Fe-oxyhydroxides and released by its reductive dissolution (Co); and (iv) metals for which release mechanisms are unclear because their behavior upon reduction is affected by changes in redox state and/or solution speciation (Cu, Cr, U and Th). Even though the process of soil Fe-oxyhydroxide reduction is important in controlling metal mobility in wetland soils, the present study showed that the dominant mechanism for this process is OM release. Thus, OM should be systematically monitored in experimental studies dedicated to understand trace metal mobility in wetland soils. Due to the fact that the process of OM release is mainly controlled by pH variations, the pH is a more crucial parameter than Eh for metal mobility in wetland soils.
Keywords: Trace metal speciation; Wetland; Organic matter; Fe reduction; pH; Redox; Natural extraction methodology;

By using a surface-modified templating method, Fe2O3@polypyrrole (PPy) core/shell spindles have been successfully prepared in this paper. The Fe2O3 particles with spindle morphology were initially fabricated as core materials. After the PVP modification, the Fe2O3 spindles were subsequently coated with a tunable thickness layer of PPy by in situ deposition of the conducting polymer from aqueous solution. Hollow PPy spindles were produced by dissolution of the Fe2O3 core from the core/shell particles. High-temperature treatment under vacuum condition covert the hollow PPy spindles into carbon capsules by carbonization of the PPy shell. Transmission electron microscope (TEM), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS) confirmed the formation of the Fe2O3@PPy core/shell particles, PPy and carbon capsules with spindle morphology.By using a surface-modified templating method, Fe2O3@polypyrrole(PPy) core/shell spindles have been successfully prepared in this paper. Hollow PPy spindles were produced by dissolution of the Fe2O3 core from the core/shell particles. High-temperature treatment under vacuum condition coverts the hollow PPy spindles into carbon capsules by carbonization of the PPy shell.
Keywords: Core/shell; Fe2O3; Polypyrrole; Spindle; Carbon;

A facile synthesis to Zn2SiO4:Mn2+ phosphor with controllable size and morphology at low temperature by Tian Jun Lou; Jing Hui Zeng; Xiang Dong Lou; Hai Li Fu; Ye Feng Wang; Rui Li Ma; Lin Jian Tong; Ya Li Chen (510-513).
Sphere- and rod-shaped Zn2SiO4:Mn2+ phosphor nanocrystals were synthesized at 230 °C. The process consists of tuning the surfactant concentration in the oil/surfactant/ethanol system. Powder X-ray (XRD) and transmission electron microscopy (TEM) were used to characterize the phase purity, size and morphology. Photoluminescent (PL) spectra were collected and analyzed. Fourier transform infrared (FT-IR) spectra of the samples indicate the removal of surfactant in the phosphor nanoparticles. As a result, the sphere-shaped phosphor nanoparticles of 100 nm in size can be redispersed in ethanol ultrasonically. The suspension maintain stable for over 48 h.
Keywords: Nanocrystal; Photoluminescence; Solvothermal; Controlled synthesis;

Stability of nano-/microsized particles in deionized water and electroless nickel solutions by B.S. Necula; I. Apachitei; L.E. Fratila-Apachitei; C. Teodosiu; J. Duszczyk (514-522).
A major problem in the co-deposition of nano- and microsized particles within electroless NiP coatings is particle dispersion in the electroless nickel solution because of the strong tendency of particles toward agglomeration and sedimentation. The stability of colloidal Al2O3, CeO2, and BN particles and Al2O3 ―CeO2 and Al2O3 ―BN particle mixtures in deionized water and electroless nickel solution was investigated by zeta potential measurements and sedimentation tests. Dispersions of Al2O3 and CeO2 particles showed good stability in deionized water with zeta potential values of 55 and 39 mV, respectively. BN dispersion in deionized water was found to be relatively unstable at pH 4 with zeta potential values of −13 mV, but at higher pH (i.e., pH 5.5), the values decreased up to about −40 mV. When the dispersions were made in electroless nickel solution, a significant decrease of the zeta potential values was observed for both single particles and mixtures of particles, indicating a change in the surface charge from high positive to low negative with detrimental effects on dispersion stability. Further, the findings suggested that the stability of particle mixtures is dominated by one type of particle, i.e., the Al2O3 ―CeO2 dispersion is governed by the single CeO2 particles, whereas the Al2O3 ―BN dispersion is governed by the Al2O3 particles. All the zeta potential measurements were in line with the results of the sedimentation tests (i.e., low zeta potential values corresponded to short settling times, whereas high zeta potential values corresponded to long settling times).The stability of single particles and mixtures of particles in deionized water and electroless nickel solution was investigated by zeta potential measurements and sedimentation tests for the synthesis of composite coatings by electroless nickel process.
Keywords: Zeta potential; Dispersion stability; Electroless nickel; Isoelectric point;

Vesicle aggregation in aqueous mixtures of negatively charged polyelectrolyte and conventional cationic surfactant by Jingxia Yao; Yuan Feng; Ying Zhao; Zichen Li; Jianbin Huang; Honglan Fu (523-530).
Vesicle aggregation induced by different environmental factors, including the addition of divalent metal ions, decrease of pH, and increase of temperature—was investigated through turbidity measurement, fluorescence measurement, and transmission electron microscope observation in aqueous solutions of hydrolyzed styrene–maleic anhydride copolymer (HSMA) mixed with dodecyltriethylammonium bromide (C12Et3). The vesicle aggregation can be explained by the dehydration of the vesicle surface through cations addition or temperature increase based on an analysis of the interaction between vesicles. Moreover, the steric repulsion was introduced to the system and the control of vesicle aggregation was achieved.Several environmental factors induced vesicle aggregation was found and investigated. The mechanism of vesicle aggregation was suggested by an analysis of the interactions between vesicles.
Keywords: Vesicle; Aggregation; Dehydration; Steric repulsion;

Amphoteric, inorganic particles used as pigments and extenders in dried coatings are not completely inert, particularly when exposed to acidity similar to atmospheric pollution, or when in a water-borne paint suspension at alkaline pH. Changes to these materials may harm the integrity of the dried coating and thus its performance during weathering or affect the colloidal stability during storage within liquid paint. The effect on aqueous titanium dioxide pigment suspensions was examined under various pH conditions. A substantial amount of aluminum was dissolved, but little silicon or titanium. Dissolution occurred at both acid and alkali pH leaving a different balance of hydrated alumina phases and overall surface composition. Changes in particle surface were apparent in topography, colloidal properties and by thermogravimetry. Such changes show that other, more complicated, changes may be possible, particularly in an aqueous paint medium where there are many other ingredients in solution or suspension.
Keywords: Hydrated alumina; Dissolution and re-precipitation; Isoelectric point; Paint films;

Stable and efficient silver substrates for SERS spectroscopy by Maurizio Muniz-Miranda; Barbara Pergolese; Adriano Bigotto; Anna Giusti (540-544).
Silver substrates have been obtained, by depositing silver colloidal nanoparticles on a roughened silver plate treated with 1,10-phenanthroline, and checked by means of AFM microscopy and Raman spectroscopy. The ligand molecules are located between two silver substrates and undergo the SERS (Surface Enhanced Raman Scattering) enhancement of both the roughened silver plate and the silver colloidal layer deposited on it. These SERS-active substrates, which show the advantages of being stable with respect to the metal colloidal suspensions, along with an easy and reproducible preparation, can be very useful for catalytic and analytical applications of the SERS spectroscopy.
Keywords: Silver; SERS; AFM; 1,10-phenanthroline;

Water structure and its influence on the flotation of carbonate and bicarbonate salts by O. Ozdemir; M.S. Çelik; Z.S. Nickolov; J.D. Miller (545-551).
Interfacial water structure is a most important parameter that influences the collector adsorption by salt minerals such as borax, potash and trona. According to previous studies, salts can be classified as water structure makers and water structure breakers. Water structure making and breaking properties of salt minerals in their saturated brine solutions are essential to explain their flotation behavior. In this work, water structure making–breaking studies in solutions of carbonate and bicarbonate salts (Na2CO3, K2CO3, NaHCO3 and NH4HCO3) in 4 wt% D2O in H2O mixtures have been performed by FTIR analysis of the OD stretching band. This method reveals a microscopic picture of the water structure making/breaking character of the salts in terms of the hydrogen bonding between the water molecules in solution. The results from the vibrational spectroscopic studies demonstrate that carbonate salts (Na2CO3 and K2CO3) act as strong structure makers, whereas bicarbonate salts (NaHCO3 and NH4HCO3) act as weak structure makers. In addition, the changes in the OD band parameters of carbonate and bicarbonate salt solutions are in agreement with the viscosity characteristics of their solutions.Water structure making/breaking in solutions of carbonate and bicarbonate salts can be revealed by FTIR analysis of the OD stretching band. The FTIR spectroscopy results are employed in the explanation of interfacial phenomena leading to the creation of the hydrophobic surface state in the flotation of these salts which is of great fundamental and practical importance.
Keywords: Interfacial water structure; Trona; Salt flotation; Water structure makers and breakers; FTIR; Carbonate and bicarbonate salts; Viscosity;

Interaction of 2-chloronaphthalene (2-CN) with high-carbon iron filings (HCIF) was studied in anaerobic batch systems, both under well-mixed and poorly-mixed conditions. In well-mixed conditions, partitioning of 2-CN between solid and aqueous phases was fast, resulting in rapid attainment of equilibrium. Equilibrium partitioning could be described by a Freundlich isotherm, C s = K . [ C a ] m , where C s (μmoles g−1 iron) and C a (μmoles L−1) were the solid and aqueous phase 2-CN concentrations, respectively. Isotherm parameters, m and K were determined to be 0.76 and 5.6 × 10 −2 (μmole g−1 iron)/(μmole L−1), respectively. Sorption ( k 2 ) and desorption ( k 3 ) rate constants were determined to be 5.60 × 10 −1   h −1 g −1 iron L and 10 h−1, respectively. Reductive dehalogenation of aqueous phase 2-CN occurred concurrently but at a slower rate, and could be described by the expression ( d C T / d t ) = − k 1 . M . ( C a ) N , where C T (μmoles L−1) was the total 2-CN concentration and M (g iron L−1) the concentration of HCIF. The values of k 1 and N were determined to be 1.09 × 10 −2   h −1 g −1 iron L and 1.647, respectively. In poorly mixed conditions, adsorption ( k 2 ) and desorption ( k 3 ) rate constants were 3.92 × 10 −5   h −1 g −1 iron L and 7 × 10 −4   h −1 , respectively, i.e., several orders of magnitude less than in well-mixed systems. The dehalogenation rate parameters, k 1 and N were determined to be 2.22 × 10 −4   h −1 g −1 iron L and 0.986, respectively, suggesting slower dehalogenation. These results highlight how mass-transfer limitations during the interaction between HCIF and 2-CN in poorly mixed systems, such as permeable reactive barriers (PRBs), can potentially impact the dehalogenation process.
Keywords: 2-Chloronaphthalene; Iron; Reductive dehalogenation; Mixing; Mass transfer limitations;

Surface characterization of electrodeposited silver on activated carbon for bactericidal purposes by Hector Ortiz-Ibarra; Norberto Casillas; Victor Soto; Maximiliano Barcena-Soto; Refugio Torres-Vitela; Wencel de la Cruz; Sergio Gómez-Salazar (562-571).
The use of an electrochemical reactor operated under different flow conditions to deposit silver from aqueous AgNO3 solutions and tartaric acid as an organic additive on a commercial activated carbon with ultimate bactericidal applications in water purification processes is presented. The characterization of carbon/silver samples was studied by BET, FTIR, X-ray diffraction, XPS, and SEM techniques. The bactericidal activity of the carbon/silver samples was tested on drinking water samples inoculated with E. coli. A reduction of carbon surface area was detected and was caused by increased amounts of silver deposited on carbon samples. Adherent silver deposits were obtained on the carbon/silver samples. X-ray diffraction studies of carbon with electrodeposited silver showed two different preferential deposition planes, [111] and [220]. The FTIR results confirm the presence of carboxyl, phenolic, quinone, and ether surface groups. The XPS results suggest the formation of Ag2O and AgO surface species and confirm the reduction of silver to the metallic form. Antimicrobial activity toward E. coli indicated reductions by up to 7 orders of magnitude in the log CFU/mL in just 10 min contact time and for silver contents of 2.47 wt%.Synthesis and characterization of silver electrodeposits on activated carbon particles are presented. Chronoamperometric and XRD results indicate a 2D nucleation silver mechanism. High antibacterial activity toward E. coli is observed.
Keywords: Silver; Activated carbon; Bactericide; XPS;

Oxybutynin chloride is an antispasmodic, anticholinergic agent indicated for the treatment of overactive bladder with symptoms of urge urinary incontinence, urgency, and frequency. Its electrochemical behavior in phosphate buffers of pH range 2–10 at a hanging mercury drop electrode has been investigated using cyclic voltammetry, differential pulse cathodic adsorptive stripping voltammetry (DPCAdSV), and squarewave cathodic adsorptive stripping voltammetry (SWCAdSV). Voltammograms of the drug in phosphate buffer of pH 2–10 exhibited a single two-electron wave and it may be attributed to the reduction of the ―CC― center. Based on the high adsorptive character of oxybutynin chloride onto the mercury electrode, a validated direct squarewave cathodic adsorptive stripping voltammetric and differential pulse cathodic adsorptive stripping voltammetric procedure has been developed for the determination of drug in bulk form and pharmaceutical formulation. The proposed SWCAdS and DPCAdS voltammetric methods allow quantitation over the range 1–18 and 1–17.6 μg mL−1 with detection limits of 0.1 and 0.23 μg mL−1, respectively. Precision and accuracy were also checked and were within the limits.Electrochemical evaluation of oxybutynin chloride in bulk and dosage form has been investigated in phosphate buffers of pH range 2–10 at a HMDE using CV, DPCAdSV and SWCAdSV over the range 1–18 μg mL−1.
Keywords: Oxybutynin chloride; Adsorptive stripping voltammetry; Mercury electrode; Pharmaceutical formulation; SWCAdSV; DPCAdSV;

The inhibitive action of the aqueous extract of olive (Olea europaea L.) leaves toward the corrosion of C-steel in 2 M HCl solution was investigated using weight loss measurements, Tafel polarization, and cyclic voltammetry. It was found that the extract acts as a good corrosion inhibitor for the tested system. The inhibition efficiency increases with increasing extract concentration. The inhibitive action of the extract is discussed with a view to adsorption of its components onto the steel surface, making a barrier to mass and charge transfer. The adsorption of extract components onto the steel surface was found to be a spontaneous process and to follow the Langmuir adsorption isotherm. It was found also that such adsorption increases the activation energy of the corrosion process. The results of cyclic voltammetry showed that the presence of olive extract decreases the charge density in the transpassive region. The inhibition efficiency is greatly reduced as the temperature is increased.The polarization curves are shifted toward more negative potentials and less current density upon addition of olive extract, indicating the inhibitive effect of olive extract.
Keywords: Corrosion inhibition; C-steel; Olive; Cyclic voltammetry;

Application of tetrahydrofuran dispersant in microemulsion for fabricating titania mesoporous thin film by Xiao Tang; Jueshi Qian; Jiamu Huang; Hua Wang; Xiaohong Zhu (584-588).
A new strategy was used to fabricate titania mesoporous thin film by incorporating tetrahydrofuran (THF) into the CTAB/n-butyl alcohol/cyclohexane/water reverse microemulsion as a micelle disperser. Highly dispersed and congregated TiO2 particles in the microemulsion with and without THF were observed by transmission electron microscopy (TEM), respectively. The photographs observed by field-emission scanning electron microscopy (FE-SEM) show that a uniform titania mesoporous thin film with monodisperse TiO2 spherical nanoparticles of ca. 20 nm was obtained using the microemulsion with THF.In the quaternary microemulsion, incorporating THF is able to disperse the reverse micelles before the hydrolysis of tetrabutyl titanate occurs in the water cores. Hence the resulting TiO2 nano-particles are spheres and highly dispersed in the microemulsion, which improves the morphology of TiO2 mesoporous thin film.
Keywords: Microemulsion; Titania; Tetrahydrofuran; Dispersant; Reverse micelle; Mesoporous thin film;

Inorganic membranes for hydrogen production and purification: A critical review and perspective by G.Q. Lu; J.C. Diniz da Costa; M. Duke; S. Giessler; R. Socolow; R.H. Williams; T. Kreutz (589-603).
Hydrogen as a high-quality and clean energy carrier has attracted renewed and ever-increasing attention around the world in recent years, mainly due to developments in fuel cells and environmental pressures including climate change issues. In thermochemical processes for hydrogen production from fossil fuels, separation and purification is a critical technology. Where water–gas shift reaction is involved for converting the carbon monoxide to hydrogen, membrane reactors show great promises for shifting the equilibrium. Membranes are also important to the subsequent purification of hydrogen. For hydrogen production and purification, there are generally two classes of membranes both being inorganic: dense phase metal and metal alloys, and porous ceramic membranes. Porous ceramic membranes are normally prepared by sol–gel or hydrothermal methods, and have high stability and durability in high temperature, harsh impurity and hydrothermal environments. In particular, microporous membranes show promises in water gas shift reaction at higher temperatures. In this article, we review the recent advances in both dense phase metal and porous ceramic membranes, and compare their separation properties and performance in membrane reactor systems. The preparation, characterization and permeation of the various membranes will be presented and discussed. We also aim to examine the critical issues in these membranes with respect to the technical and economical advantages and disadvantages. Discussions will also be made on the relevance and importance of membrane technology to the new generation of zero-emission power technologies.Simplified concept schematic of membrane separation.
Keywords: Membranes; Dense metal membranes; Porous membranes; Hydrogen production; Hydrogen purification;

We applied the concepts of nonextensive thermodynamics [Turmine et al., J. Phys. Chem. B 108 (2004) 18980], to describe the equilibrium of a liquid drop placed on a solid substrate. This approach provides a consistent formal framework for analyzing the contact angle according to the nature and structure of the substrate, and also the size of the drops. The introduction, for the solid/liquid interface, of the concept of “fuzzy interface” characterized by a thermodynamic dimension, different from 2/3 (surface) allowed description of the case of substrates with ill-defined geometry (such as porous, structured systems, fractal structure systems, etc.) and straightforward explanation of the phenomenon of super hydrophobicity without using a layer of trapped air in possible anfractuosities. The application of the nonextensive thermodynamics relationships, allowed explanation of all the usual behaviors described in the literature (Young, modified Young, Wenzel, Cassie–Baxter) including the case of the composite interfaces made of materials with different natures and spatial structures (smooth, rough, homogeneous and heterogeneous surfaces). We show that the contact angle can vary with the drop volume according to a power law, and this was validated against values published in the literature. This study also has consequences for the relations between “thermodynamic dimension” and “fractal dimension.”Concepts of nonextensive thermodynamics are applied to describe the sessile drop equilibrium. The solid–liquid interface is considered as a nonextensive phase characterized by an extensity χ SL and a thermodynamic dimension m.
Keywords: Contact angle; Nonextensive thermodynamics; Drop size; Fuzzy interface;

Using the polystyrene (PS) colloidal monolayers as templates, ordered indium oxide pore array films with different morphologies were prepared by sol-dipping method. These porous films took on hydrophilicity, however, after chemical modification, such pore array films displayed both superhydrophobicity and lipophobicity due to rough surface and low surface free energy materials on their surfaces. Interestingly, with increase of the pore size in the films, the superhydrophobicity could be controlled and was gradually enhanced due to the corresponding increase of roughness caused by nanogaps produced by the thermal stress in the annealing process with increase of film thickness.The porous In2O3 films displayed both superhydrophobicity and lipophobicity due to rough surface and low free energy materials on their surfaces.
Keywords: Superhydrophobic; Lipophobic; Indium oxide; Macropore array film; Nanogaps;

Surface tensions of imidazolium based ionic liquids: Anion, cation, temperature and water effect by Mara G. Freire; Pedro J. Carvalho; Ana M. Fernandes; Isabel M. Marrucho; António J. Queimada; João A.P. Coutinho (621-630).
This work addresses the experimental measurements of the surface tension of eight imidazolium based ionic liquids (ILs) and their dependence with the temperature (288–353 K) and water content. The set of selected ionic liquids was chosen to provide a comprehensive study of the influence of the cation alkyl chain length, the number of cation substitutions and the anion on the properties under study. The influence of water content in the surface tension was studied for several ILs as a function of the temperature as well as a function of water mole fraction, for the most hydrophobic IL investigated, [omim][PF6], and one of the more hygroscopic IL, [bmim][PF6]. The surface thermodynamic functions such as surface entropy and enthalpy were derived from the temperature dependence of the surface tension values.
Keywords: Surface tension; Ionic liquids; Imidazolium based ionic liquids; Temperature dependence; Water content; Effective ionic concentration; Molar conductivity; Critical temperature;

A moving circular wave front forms after a small droplet of aqueous surfactant solution is deposited on a thin aqueous layer. The time evolution of the radius of the moving front was monitored. Surfactants of different solubility were used at concentrations above CMC. It is shown that the time evolution of the moving front proceeds in two stages: a rapid first stage, which is followed by a slower second stage. It is shown that the time evolution of the moving front substantially depends on the surfactant solubility. An exact solution for the evolution of the moving front was deduced for the case of insoluble surfactants. A qualitative theory was developed to account for the influence of the solubility on the front motion. Our experimental observations are in a good agreement with the theory predictions.
Keywords: Surfactant solutions; Solubility; Marangoni effect;

We report measurements of self aggregation in aqueous solution of an ionic liquid (IL), didecyl-dimethylammonium nitrate ([DDA][NO3]) and a surfactant hexadecyl-trimethylammonium bromide (CTAB) and of mixtures of these two salts. The electrical conductivity and dynamic light scattering (DLS) measurements were used for the characterization of the aggregation process. The conductivity measurements were performed at three temperatures. The critical micelle concentration (CMC) was determined at different temperatures and at different ratio of two salts. The effect of IL on the micellization of CTAB has been discussed. Our results suggest that organized structures formed by CTAB and [DDA][NO3] self assembly in domains of several hundred nanometers size. The micellar solubility of the salicylic acid in mixed salt aqueous solutions was determined to probe the physical properties of these assemblies. We have observed, that the micellar solubility enhancement was only slightly influenced by the nature of micelles present in aqueous solution. This proves that salicylic acid solubilization is enthalpy driven.Measurements of self aggregation in aqueous solution of an ionic liquid (IL), didecyl-dimethylammonium nitrate ([DDA][NO3]) and a surfactant hexadecyl-trimethylammonium bromide (CTAB) and of mixtures of these two salts are reported.
Keywords: Ionic liquid; Surfactant; Electrical conductivity; DLS; Micellization;

Cationic Gemini surfactant at the air/water interface by Chen Qibin; Liang Xiaodong; Wang Shaolei; Xu Shouhong; Liu Honglai; Hu Ying (651-658).
The surface properties and structures of a cationic Gemini surfactant with a rigid spacer, p-xylyl-bis(dimethyloctadecylammonium bromide) ([C18H37(CH3)2N+ ―CH2 ―C6H4 ―CH2 ―N+(CH3)2C18H37],2Br, abbreviated as 18-Ar-18,2Br−1), at the air/water interface were investigated. It is found that the surface pressure–molecular area isotherms observed at different temperatures do not exhibit a plateau region but display an unusual “kink” before collapse. The range of the corresponding minimum compressibility and maximum compressibility modulus indicates that the monolayer is in the liquid-expanded state. The monolayers were transferred onto mica and quartz plates by the Langmuir–Blodgett (LB) technique. The structures of monolayers at various surface pressures were studied by atomic force microscopy (AFM) and UV–vis spectroscopy, respectively. AFM measurements show that at lower surface pressures, unlike the structures of complex or hybrid films formed by Gemini amphiphiles with DNA, dye, or inorganic materials or the Langmuir film formed by the nonionic Gemini surfactant, in this case network-like labyrinthine interconnected ridges are formed. The formation of the structures can be interpreted in terms of the spinodal decomposition mechanism. With the increase of the surface pressure up to 35 mN/m, surface micelles dispersed in the network-like ridges gradually appear which might be caused by both the spinodal decomposition and dewetting. The UV–vis adsorption shows that over the whole range of surface pressures, the molecules form a J-aggregate in LB films, which implies that the spacers construct a π – π aromatic stacking. This π – π interaction between spacers and the van der Waals interaction between hydrophobic chains lead to the formation of both networks and micelles. The labyrinthine interconnected ridges are formed first because of the rapid evaporation of solvent during the spreading processes; with increasing surface pressure, some of the alkyl chains reorient from tilting to vertical, forming surface micelles dispersed in the network-like ridges due to the strong interaction among film molecules.The figure represents the variation of surface pressure with the molecular area during compression. It shows that the isotherms resemble to each other. On the whole, as surface pressure increases, the curves do not exhibit a plateau region characterizing a definable sharp phase transition. The π – A isotherms of 18-Ar-18,2Br−1 at different temperatures. The insert gives an enlarged section adjacent to the maximum of the surface pressure.
Keywords: Gemini surfactant; LB film;

Aqueous sodium dehydrocholate–sodium deoxycholate mixtures at low concentration by Marcos D. Fernández-Leyes; Paula V. Messina; Pablo C. Schulz (659-664).
The behavior of the sodium dehydrocholate (NaDHC)–sodium deoxycholate (NaDC) mixed system was studied by a battery of methods that examine effects caused by the different components of the system: monomers, micelles, and both components. The behavior of the mixed micellar system was studied by the application of Rubingh's model. The obtained results show that micellar interaction was repulsive when the aggregates were rich in NaDHC. The gradual inclusion of NaDC in micelles led to a structural transformation in the aggregates and the interaction became attractive. The bile salts' behavior in mixed monolayers at the air–solution interface was also investigated. Mixed monolayers are monotonically rich in NaDC, giving a stable and compact adsorbed layer. Results have shown that the interaction in both micelles and monolayer is not ideal and such behavior is assumed to be due to a structural factor in their hydrocarbon backbone.In addition to their physiological roles, bile salts mixed micelles are promising systems for drug delivery. The purpose of this research was to attempt to shed further light on the process of bile salts mixed micelles and mixed monolayer formation. These kinds of systems could be considered the simplest model to get molecular information and hence, this study is the first step to understand the properties and the behavior of macromolecular assemblies.
Keywords: Sodium deoxycholate; Sodium dehydrocholate; Mixed aggregates; Mixed monolayers; Bile salts; Rubingh's model;

The micelle–water partition coefficients of 81 organic compounds in SDS solution were predicted by quantitative structure–property relationship method. The multiple linear regression (MLR) and artificial neural network (ANN) techniques were used to build linear and nonlinear model, respectively. In this work the proposed QSPR models, both by MLR and ANN, contain identical descriptors which are zero order of Kier–Hall index, count of Hydrogen donors site [Zefirovs PC], average valency of a C atom, atomic charge weighted by partial positively charged surface area and minimum one electron reaction index for a C atom. The MLR model gave a root mean square (RMS) of 0.166, 0.25, and 0.289 for training, prediction and test sets, respectively, whereas ANN gave an RMS error of 0.06, 0.21, and 0.20 for training, prediction, and test sets, respectively. Comparison the results of these two methods reveals that those obtained by the ANN model are much better.In this work, ANN was used for predicting K mw of some organic compounds, using theoretical descriptors.
Keywords: Micelle–water partition coefficient; Multiple linear regressions; Artificial neural network; Quantitative structure–property relationship; Theoretical molecular descriptor;

Solubilization in monodisperse emulsions by Suwimon Ariyaprakai; Stephanie R. Dungan (673-682).
The kinetics of oil solubilization into micelles from nearly monodisperse alkane-in-water emulsion droplets was investigated. Emulsions containing either hexadecane or tetradecane oils were fractionated to be narrowly distributed, using a method developed by Bibette [J. Bibette, J. Colloid Interface Sci. 147 (1991) 474]. These monodisperse emulsions were mixed with SDS or Tween 20 aqueous micellar solutions of various concentrations. Time-dependent solubilization was monitored using light scattering and a decrease in average droplet size over time was observed, in contrast to what has been observed previously with polydisperse emulsions. The rate at which the droplet size decreased was found to be independent of the initial droplet size. Turbidity measurements were also used to track the solubilization kinetics, and a population balance analysis used on both types of measurements to extract effective mass transfer coefficients. The dependence of these transfer coefficients on droplet size, alkane type, surfactant type and concentration provide insights into plausible mechanisms of emulsion droplet solubilization within micellar solutions.
Keywords: Solubilization; Monodisperse emulsions; Mass transfer coefficient; Population balance;

Spectroscopic study on the precipitation of sodium alkyl sulfate with cetylpyridinium chloride by Hwan Young Song; Sun Wha Oh; Sung Doo Moon; Young Soo Kang (683-688).
The precipitation of sodium alkyl sulfate with cetylpyridinium chloride was obtained under optimized conditions. The conditions for the most efficient formation of precipitates were obtained as longer alkyl chain length of alkyl sulfate (C14), higher pH (pH 12), 1.5 M NaCl, and equimolar ratio between anionic and cationic surfactants. The structures and physical properties of surfactant precipitates were investigated with SEM, UV–vis, and FT-IR spectroscopy and light scattering. The precipitate of sodium alkyl sulfate with cetylpyridinium chloride was studied with the pressure–area isotherm at the air/water interface. In addition, the surface morphology of the Langmuir–Blodgett film of surfactant precipitate was observed with atomic force microscopy.The precipitation of sodium alkyl sulfate with cetylpyridinium chloride was obtained under optimized conditions. The shape of the surfactant precipitates is affected by the equilibrium between hydrophobic and electrostatic interaction of the surfactant.
Keywords: Surfactant precipitate; Sodium alkyl sulfate; Cetylpyridinium chloride; SEM; UV–vis; FT-IR; Light scattering; AFM;

Behavior of acetyl modified amino acids in reverse micelles: A non-invasive and physiochemical approach by S.K. Mehta; Khushwinder Kaur; Shweta Sharma; K.K. Bhasin (689-698).
The well-characterized, monodisperse nature of reverse micelles formed by sodium bis-(2-ethylhexyl)sulfosuccinate/water/isooctane and their usefulness in assimilating compounds of varied interests have been exploited to investigate the effect of acetyl modified amino acids (MAA) viz., N-acetyl-l-glycine (NAG), N-acetyl-l-aspartic acid (NAA) and N-acetyl-l-cysteine (NAC), on the water pool and physiochemical properties. Non-invasive techniques such as FTIR and UV–vis absorption spectroscopy have been employed to analyze the interactions of MAA with core water and the AOT headgroup. The micropolarities on both sides of AOT interface have further been investigated by UV–vis absorption probes, methyl orange (MO) and methylene blue (MB). The dynamics of water and temperature induced percolation process have also been studied. The MAA molecules have been found to assist the process with the increase in water content where as a contrary behavior has been observed with the increase in temperature. Conductivity results have been further rationalized in terms of scaling equations, which delineate the dynamic nature of the percolation process. The results have also been analyzed in the light of activation energy of the percolation process and thermodynamics of droplet clustering.The effect of acetyl modified amino acids (MAA) viz. N-acetyl-l-glycine (NAG), N-acetyl-l-aspartic acid (NAA) and N-acetyl-l-cysteine (NAC), on the water pool and physiochemical properties of sodium bis-(2-ethylhexyl)sulfosuccinate/water/isooctane reverse micelles have been studied to delineate the probable changes.
Keywords: Modified amino acids; Non-invasive techniques; Water and temperature induced percolation;

Surface and bulk properties of aqueous decyltrimethylammonium bromide–hexadecyltrimethylammonium bromide mixed system by J.L. Rodríguez; M.B. Sierra; P.V. Messina; M.A. Morini; P.C. Schulz; P. del Burgo; E. Junquera; A. Rodríguez; E. Aicart (699-706).
The aqueous mixed system decyltrimethylammonium bromide (C10TAB)–hexadecyltrimethylammonium bromide (C16TAB) was studied by conductivity, ion-selective electrodes, surface tension, and fluorescence spectroscopy techniques. The mixture critical micelle concentration, cmc*, aggregation number, N ∗ , and micelle molar conductivity, Λ M cmc , showed that the system aggregation is strongly nonideal. Both cmc* and N ∗ results were analyzed with two different procedures: (i) the regular solution theory on mixed micelles or Rubingh's theory, and (ii) by the determination of the partial critical micelle concentration of the amphiphile component i in the presence of a constant concentration of the other amphiphile component, cmc i ∗ . The Rubingh procedure gives micelles richer in C16TAB than the overall mixtures, while procedure (ii) gives micelles having the same composition as in the complete surfactant mixture ( α C 10 TAB ). Mixed micelles are larger than pure surfactant ones, with nonspherical shape. Using a literature model, the cause of the synergistic effect seems to be a reduction of the hydrocarbon/water contact at the micelle surface when mixed micelles form. Conductivity and ion-selective electrodes indicate that highly ionized premicelles form immediately before the cmc*. The air/solution interface is strongly nonideal and much richer in C 16 TAB than the composition in the bulk. When micelles form there is a strong desorption from the air/solution interface because micelles are energetically favored when compared with the monolayer.The aqueous mixed system C10TAB–C16TAB was studied by conductivity, ion-selective electrodes, surface tension, and fluorescence spectroscopy. Results were analyzed by the regular solution theory, and by the partial critical micelle concentration of one component in the presence of a constant concentration of the other one.
Keywords: Aggregation number; Conductivity; Critical micelle concentration; Decyltrimethylammonium bromide; Fluorescence; Hexadecyltrimethylammonium bromide; Ion-selective electrodes; Surface tension;

Surface and micelle properties of novel multi-dentate surfactants by Nan Gao; Jinfeng Dong; Gaoyong Zhang; Xiaohai Zhou; Julian Eastoe; Kevin J. Mutch; Richard K. Heenan (707-711).
Novel multi-dentate surfactants, based on alkyl amines of varying hydrophobicity were synthesized, and molecular structures were characterized by IR, UV–vis, NMR and FAB-MS. The new surfactants have good water solubility and are highly efficient at reducing aqueous surface tension. Small-angle neutron scattering (SANS) studies were carried out with aqueous solutions in D2O to study aggregation. Spherical micelles were shown to form, and these grow with increasing alkyl chain length; their conformation is unusual compared to conventional linear chain surfactants.Spherical micelles are shown to form in aqueous solutions of new multi-dentate amine surfactants. The micelle size depends on surfactant chain length. However, compared to conventional linear chain, single headed surfactants, the micelle structures appear to be subtly different, in that there is no evidence for strong headgroup hydration.
Keywords: Multi-dentate surfactants; Micelle; Small-angle neutron scattering;

Efforts were made to prepare bicontinuous microemulsions with ten different oil phases involving aliphatic, linear, and aromatic hydrocarbons as oil phases, two co-surfactants (n-butanol and n-pentanol) and two surfactants: cationic (CTAB) and anionic (SDS). Different weight percentages were employed for the preparation of cationic and anionic surfactant based microemulsions as reported in the literature. Out of the 40 compositions (10 oil phases × 2 co-surfactants × 2 surfactants) thus selected only 28 systems showed stable bicontinuous microemulsion phase. This behavior is explained on the basis of the structures of various constituents present in the microemulsions. Viscosity variations of stable bicontinuous microemulsions are found to depend mainly on the nature of co-surfactant. Conductivity behavior on the other hand depends mainly on the weight percentage and composition of aqueous phase. The solubility of pyrene in the oil phase determines the excimer formation and fluorescence behavior in microemulsions. The electron transfer property of both the water-soluble and the oil-soluble redox systems does not depend on the oil phase and the co-surfactant. The significance and importance of characterizing well defined bicontinuous microemulsions is thus highlighted.In the four-component microemulsion systems viscosity depends on the co-surfactant structure, conductivity depends on the composition of aqueous phase, and fluorescence depends on the oil phase structure. The electrochemical properties of the redox systems do not depend on constituent structures.
Keywords: Bicontinuous microemulsion; Viscosity; Conductivity; Fluorescence; Electron transfer;

Competitive solubilization of cholesterol and phytosterols in nonionic microemulsions by Shoshana Rozner; Abraham Aserin; Ellen J. Wachtel; Nissim Garti (718-726).
It is well documented that phytosterols inhibit the uptake of exogenic cholesterol and do not interfere with cholesterol synthesis or cause side effects. The mechanism by which phytosterols interfere with cholesterol absorption is not completely clear and there are at least three hypotheses for their beneficial activity. Among these is that of competitive solubilization of phytosterols and cholesterol in dietary mixed micelles. In the present study we investigated the competitive solubilization of phytosterols (approximately 50% β-sitosterol) and cholesterol in a nonionic microemulsion system constructed as a model for the dietary mixed micelles. We studied the effect of the competitive solubilization of cholesterol and phytosterols on the structural transformations and physical properties of the microemulsion and evaluated the locus of the solubilizates within the nanodroplets of each sterol separately and when they are loaded together at different weight ratios along one dilution line. Our results show that chemical and structural differences between cholesterol and phytosterols significantly influence the solubilization capacity of the nonionic microemulsion. Cholesterol, being more amphiphilic, is solubilized more efficiently at the W/O microemulsion interface, while in the O/W microemulsion phytosterols are dissolved somewhat more efficiently in the droplet core.Cholesterol is solubilized more effectively at a W/O microemulsion interface than phytosterols which reside preferentially within the lipophilic core of the nanodroplets once O/W is formed.
Keywords: Cholesterol; Phytosterols; Competitive solubilization; CHD; CVD; Microemulsions; Solubilization; Viscosity; Phase diagram; Small angle X-ray scattering;

The onset of Rayleigh–Marangoni convection in a vertical annulus heated from below is investigated using linear stability analysis. The results of the present study also show the pattern transitions as a function of scaled gap width and aspect ratio. It is concluded that Marangoni convection can change the fluid pattern in an otherwise pure Rayleigh problem. It is also concluded that the gap width cannot significantly change the Marangoni effect as it is essentially the depth of liquid and Biot number that play a dominant role.Strong Marangoni convection can significantly change the fluid pattern in an otherwise pure Rayleigh problem. In a cylindrical annulus, the gap width cannot significantly change the Marangoni effects.
Keywords: Rayleigh–Marangoni convection; Pattern formation; Instability; Bifurcation; Annulus;

Ionic transport in porous media for high zeta potentials by A.K. Gupta; D. Coelho; P.M. Adler (733-747).
Ionic transport coefficients are numerically calculated in various porous media for high zeta potentials ζ by solving the Poisson–Boltzmann, the Stokes, and the convection–diffusion equations on the pore scale. Theoretical formulae for the simple case of a plane Poiseuille flow are derived in this limit. These formulae, when expressed in terms of the characteristic length Λ, provide an excellent estimate of the ionic transport coefficients whatever the porous medium and whatever the value of ζ.For various porous media, the coefficients coupling the external macroscopic gradients and the macroscopic solute fluxes are shown to follow the semianalytical solution derived for a plane Poiseuille flow (solid lines).
Keywords: Porous media; Electrokinetics; Zeta potential; Diffusion coefficients;

by Arthur Hubbard (748).