Journal of Colloid And Interface Science (v.343, #2)

Cover 1 (OFC).

Inhomogeneities in sodium decylsulfate doped 1,2-dipalmitoylphosphatidylcholine bilayer by O. Ortona; V. Vitagliano; D. Fessas; P. Del Vecchio; G. D’Errico (401-407).
Differential scanning calorimetry (DSC), dynamic light scattering (DLS), and turbidity measurements have been used to study the effect of sodium decylsulfate, C10OS, on 1,2-dipalmitoylphosphatidylcholine, DPPC, vesicles. DSC measurements, performed soon after addition of C10OS solutions to DPPC vesicular dispersion, at several C10OS/DPPC molar ratios, showed the contemporary presence of maxima ascribable both to transitions of an unmodified DPPC membrane and to transitions related to membrane domains in which C10OS is also present.In all the considered samples only unilamellar vesicles are present as shown by DLS measurements carried out on aqueous DPPC and C10OS–DPPC systems. Also the aging of the samples confirmed the presence of SUV in the time scale of DSC measurements.On the basis of DSC results the pseudo-phase diagram of the system was drawn. This diagram does not represent a system in equilibrium, from a thermodynamic point of view, but only kinetically probable states. In fact the prolonged aging of the solutions used both for DSC and DLS scans highlight the disappearance of the unmodified DPPC membrane and its conversion into a mixed membrane. Turbidity measurements at 25 °C, performed as a function of surfactant composition, showed that C10OS initially contributes to increase the vesicles dimensions and allowed to calculate the saturation ratio C10OS/DPPC in the membrane. In contrast, at 45 °C the presence of surfactant gives origin immediately to smaller structures in comparison to vesicles, probably gel-state micelles.
Keywords: Lipid bilayer; Surfactant; Lipid–surfactant interaction; DSC; DLS; Lipid–surfactant distribution;

Aggregation kinetics of pristine topsoil colloids under different Ca2+ concentration conditions.The goals of the study were to investigate the effects of the soil–water phase ionic strength, mainly monitored by the calcium ion (Ca2+) concentration, on the stability behavior of easily dispersed topsoil colloidal clay-sized particles (<2 μm). The aggregation kinetics as a function of the Ca2+ concentration was monitored by measuring the increase of the particle size over time with photon correlation spectroscopy. The critical coagulation concentrations (CCC) of Ca2+ were measured. The Hamaker constants (A) characterizing the attractive chemical properties of the topsoil colloid surface were thus scaled according to the Derjaguin, Landau, Verwey, Overbeek (DLVO) theory by taking into account the electrokinetic behavior of the particles, measured by the ζ-potential. Effective values for the Hamaker constants of topsoil clay-sized colloids, clay minerals, and metal oxides were calculated by referring to reported values for crystalline silica or sand (quartz) particles. Potential-energy diagrams of interacting topsoil clay-sized colloids were calculated. The primary energy maximum and secondary energy minimum were used for modeling the aggregation kinetics along the Ca2+ concentration by employing Marmur’s model. Coagulation in the secondary energy minimum can only explain the aggregation efficiency of topsoil colloids at low Ca2+ concentrations (<2 mM Ca2+) under unfavorable electrostatic conditions. The effect of surface-associated organic matter on the colloidal electrosteric stability was also investigated by comparing the topsoil colloid stability after the removal of organic matter.
Keywords: Topsoil colloid; Aggregation kinetics; Ca2+; Energy minimum; Hamaker constant; Electrosteric stabilization;

Surfactant-assisted route to fabricate CoFe2O4 individual nanoparticles and spherical assemblies by Carla Cannas; Andrea Ardu; Davide Peddis; Claudio Sangregorio; Giorgio Piccaluga; Anna Musinu (415-422).
Individual CoFe2O4 nanoparticles and their organization in secondary spherical assemblies.A surfactant-assisted route in aqueous media has been shown to be suitable to prepare either individual primary CoFe2O4 nanocrystals or secondary spherical nanoporous assemblies with a high surface area. The formation of primary nanoparticles or of spherical assemblies is found to be dependent on the presence of the surfactant and on the particle size, but is shown that the nanoparticle–surfactant interface plays a dominant role. The size of the primary CoFe2O4 particles is controlled by the type of salt, the synthesis temperature and the concentration of the precursors. A detailed characterization evidences the shape and size of the primary particles, the way in which the primary particles assemble and their features in terms of morphological, textural and magnetic properties.
Keywords: Surfactant-assisted routes; Cobalt ferrite; Magnetic properties; Transmission electron microscopy;

Characterization of water/AOT/benzene microemulsions during photoreduction to produce silver particles by Masafumi Harada; Kenji Saijo; Naoki Sakamoto; Kazuki Ito (423-432).
Time evolution of the SAXS profiles and the representative TEM image for the Ag colloidal dispersions prepared by the photoreduction in the water/AOT/benzene water-in-oil (w/o) microemulsions.Colloidal dispersions of silver (Ag) particles were prepared by the photoreduction of silver perchlorate (AgClO4) in water/AOT/benzene water-in-oil (w/o) microemulsions consisting of sodium bis(2-ethylhexyl) sulfosuccinate (AOT), water and benzene. Formation mechanisms of Ag particles prepared in the presence of benzoin by photoreduction from Ag+-containing w/o microemulsions were investigated by UV–vis, transmission electron microscopy (TEM), extended X-ray absorption fine structure (EXAFS) and small-angle X-ray scattering (SAXS) measurements. By a combination of TEM and EXAFS results, Ag particles show a metallic nature after the photoreduction and the diameter of Ag particles ranges between 5 and 30 nm. In situ time-resolved SAXS measurements show that the integrated rate equation can be applied in the reduction process of Ag+ ions to Ag0 atoms, and the autocatalytic Ag particle growth proceeds in the association process of Ag0 atoms during the photoreduction of Ag+-containing w/o microemulsions. The nanometer-sized water droplets microemulsified by AOT in benzene continuous-phase regulated the size of Ag particles, and the size and shape of water droplets were retained during the Ag particle formation.
Keywords: Colloidal dispersions; Silver particles; Water-in-oil (w/o) microemulsions; Surfactant-stabilized silver particles; Photoreduction; EXAFS; In situ SAXS;

Dissolution of anisotropic colloidal mineral particles: Evidence for basal surface reactivity of nontronite by Malgorzata Grybos; Laurent J. Michot; Michal Skiba; Patrick Billard; Christian Mustin (433-438).
A study of the dissolution of size-selected colloidal nontronite particles immobilized in a silica gel reveals that the basal face of nontronites plays a significant role in the weathering process.Anisotropic textural and crystallographic properties of phyllosilicate particles often influence the mineral weathering rate. The purpose of this study was to investigate how the changes in mineral surfaces (basal vs. edge) as a result of changes in crystal size control the dissolution of the mineral. Different nano-size fractions of Na-exchanged nontronites (NAu2 and NAu1) were immobilized in a silica gel and then incubated under acidic conditions using HNO3 at 28 °C for 5 days. For each sample, the dissolution behavior was analyzed by measuring the amount of iron released from the mineral lattice. The results showed that for a given pH, a decrease in particle size significantly increased NAu2 and NAu1 dissolution. At pH 1.5, 7.2% of the total iron of the highest size sample of NAu2 was released in solution whereas this proportion increased up to 25% for the smallest size fraction. The percentage of total iron extracted from NAu1 at the same pH (1.5) was less important: 3.5% and 6.5% for higher and smaller size fractions, respectively. The observed increase in dissolution was not directly correlated to the increase in the amount of edge faces, suggesting that all mineral surfaces contributed to mineral dissolution. In the present case this may be related to the fact that 8% and 2% of total iron of NAu2 and NAu1, respectively, are located in the tetrahedral sheet. In conclusion, the basal surface of nontronites plays an important role in the weathering process.
Keywords: Phyllosilicates; Dissolution; Surface reactivity; Colloids; Nontronite;

Synthesis of sulfur nanoparticles in aqueous surfactant solutions by Rajib Ghosh Chaudhuri; Santanu Paria (439-446).
Formation of sulfur nanoparticles by acid catalyzed precipitation of thiosulphate in aqueous surfactant solutions: the smallest particle size is generated in the presence of CTAB.Sulfur is a widely used element in different applications such as fertilizers, pharmaceuticals, rubber, fiber industries, bioleaching processes, anti microbial agents, insecticides, and fumigants, etc. Nanosize sulfur particles are useful for pharmaceuticals, modification of carbon nano tubes, and synthesis of nano composites for lithium batteries. In this study we report a surfactant assisted route for the synthesis of sulfur nanoparticles by an acid catalyzed precipitation of sodium thiosulphate. We use both the inorganic and organic acids, and find that organic acid gives lower size sulfur particles. The size of the particles also depends on the reactant concentration and acid to reactant ratio. The effect of different surfactants (TX-100, CTAB, SDBS, and SDS) on particle size shows that the surfactant can significantly reduce the particle size without changing the shape. The size reducing ability is not same for all the surfactants, depending on the type of surfactant. The anionic surfactant SDBS is more effective for obtaining a uniform size in both the acid media. Whereas, the lowest size (30 nm) particles were obtained in a certain reactant concentration range using CTAB surfactant. The objective of this study is to synthesize sulfur nanoparticles in aqueous media and also study the effect of different surfactants on particle size.
Keywords: Sulfur nanoparticle; Aqueous surfactant solution; Interparticle exchange; Film flexibility; Nucleation;

UV–vis absorption spectra of silver nanoparticles synthesized using different reducing sugars depend on the chemical reaction rates with different saccharides.Synthesis of silver nanoparticles in homogeneous aqueous solutions of the precursors silver nitrate and three saccharides (two mono saccharides i.e. glucose and fructose and one disaccharide such as sucrose) has been performed. These Ag-nanoparticles can be derivatized by other surface treatments, as required. The anionic surfactant SDS was tested to investigate its effect on the dependence of size, growth rate, photoluminescence (PL) emission and polydispersity of the nanoparticles. The time evolution of UV–vis absorbance suggested that nucleation and growth rate markedly vary in a first order fashion w.r.t. Ag+ salt concentration. The differences in the reducing ability of the saccharides were discussed with reference to their structure dependent adsorption behavior onto the particles. Changes in UV–vis, PL and FT-IR spectra during nucleation and growth of the nanoparticles were used to establish plausible mechanisms for the adsorption of surfactant on the particle surface, so as to restrict the growth. The results revealed a simple and easy strategy for synthesizing metal nanoparticles with well controlled shapes, sizes and structures.
Keywords: Silver nanoparticles; Saccharides; Photoluminescence (PL) emission; Nucleation; Plausible mechanism;

Order of propensity to aggregate for different conformations of BSA upon addition of CTAB is: denatured > intermediate > native.To characterize the structural changes in bovine serum albumin (BSA) on the addition of N-cetyl-N,N,N-trimethyl ammonium bromide (CTAB) and to understand the mechanism underlying aggregation of resulting protein–surfactant complex, UV–visible absorbance, steady-state fluorescence, SDS–PAGE gel electrophoresis, dynamic light scattering (DLS), and circular dichroism measurements of BSA–CTAB solutions were carried out. Changes in UV–visible absorbance and the fluorescence intensity on the addition of CTAB indicate the binding of CTAB to BSA. Changes in SDS–gel pattern of pepsin digested BSA sample, circular dichroism band at 222 nm, ANS intensity of BSA–ANS solution and hydrodynamic diameter of native state monomer on the addition of CTAB indicate that BSA unfolds in the presence of CTAB. Changes in the heme binding profile, temperature dependence of the heme binding profile and change from mixed to dynamic quenching in acrylamide quenching experiments of BSA solution on the addition of CTAB indicate that BSA unfolds to an intermediate. Turbidity and DLS measurements at 298 K, 323 K and 358 K indicate that the order of propensity to aggregate for different conformations of protein is: denatured > intermediate > native. The formation of aggregates is influenced by the nature of head and tail of the surfactant.
Keywords: Bovine serum albumin; Aggregation; Intermediates; Protein–surfactant interaction; Fluorescence; Dynamic light scattering;

Adsorption of hazardous dye crystal violet from wastewater by waste materials by Alok Mittal; Jyoti Mittal; Arti Malviya; Dipika Kaur; V.K. Gupta (463-473).
Effect of pH on the uptake of crystal violet over bottom ash and de-oiled soya.The adsorption performance of the materials bottom ash (BA), a power plant waste, and de-oiled soya (DOS), a soya bean industry waste for removal of crystal violet dye, has been investigated through batch and column experiments. Batch studies have been performed to describe the impact of parameters such as pH, amount of adsorbent, dye concentration, temperature, and contact time on the removal of the dye. Experimental data have been modeled by using Langmuir, Freundlich, Tempkin, and Dubinin–Radushkevich (D–R) isotherms. Thermodynamic parameters (ΔG°, ΔH°, and ΔS°) were evaluated for the dye–adsorbent systems, which revealed that the adsorption process is endothermic in nature. Pseudo-first- and second-order kinetic models have been applied to the experimental data and pseudo-second-order kinetics was found to describe the adsorption of the dye (crystal violet) on the adsorbents. In order to achieve bulk removal of the dye, column operations were made. Recovery of the dye was made by eluting HCl solution through the exhausted columns and almost 95% and 78% of the dye was recovered from BA and DOS columns, respectively.
Keywords: Adsorption; Dyes; Bottom ash; De-oiled soya; Crystal violet;

Development of protective coatings with optimum corrosion resistance requires an understanding of the deposition mechanisms. This paper demonstrates that the solution chemistry in the coating bath has a significant impact on the nature of organosilane films on magnesium.Magnesium alloys have a low specific density and a high strength to weight ratio. This makes them sought after light weight construction materials for automotive and aerospace applications. These materials have also recently become of interest for biomedical applications. Unfortunately, the use of magnesium alloys in many applications has been limited due to its high susceptibility to corrosion. One way to improve the corrosion resistance of magnesium alloys is through the deposition of protective coatings. Many of the current pretreatments/coatings available use toxic chemicals such as chromates and hydrofluoric acid. One possible environmentally friendly alternative is organosilane coatings which have been shown to offer significant corrosion protection to both aluminum alloys and steels. Organosilanes are ambifunctional molecules that are capable of covalent bonding to metal hydroxide surfaces. In order for covalent bonding to occur, the organosilane must undergo hydrolysis in the coating bath followed by a condensation reaction with the surface. There are a number of factors that influence the rates of these reactions such as pH and concentration of reactants. These factors can also influence competing reactions in solution such as oligomerization. The rates of hydrolysis and condensation of 3-mercaptopropyltrimethoxy silane in methanol have been analyzed with 1H NMR and ATR–FTIR. The results indicate that organosilane oligomers begin to form in solution before the molecules are fully hydrolyzed. The organosilane films deposited on magnesium alloy AZ91 at a variety of concentrations and pre-hydrolysis times were characterized with a combination of ATR–FTIR, ellipsometry and SEM/EDS. The results show that both organosilane film thickness and uniformity are affected by the chemistry occurring in the coating bath prior to deposition.
Keywords: Organosilane; Magnesium; Coatings; Hydrolysis; Condensation; ATR–FTIR;

Monodisperse and fluorescent poly(styrene-co-methacrylic acid-co-2-naphthyl methacrylate)/Fe3O4 composite particles by Patakamuri Govindaiah; Yeon Jae Jung; Jung Min Lee; Tae-Joon Park; Du Yeol Ryu; Jung Hyun Kim; In Woo Cheong (484-490).
New types of fluorescent and magnetic composite particles were developed by emulsifier-free emulsion polymerization and immobilization process. Monodisperse poly(St/MAA/NMA)/Fe3O4 composite particles exhibit both luminescent and magnetic properties.This article describes the preparation and characterization of fluorescent and magnetic composite particles of poly(styrene-co-methacrylic acid-co-2-naphthyl methacrylate) (poly(St/MAA/NMA)). First, monodisperse (Dw /Dn  < 1.1) and fluorescent poly(St/MAA/NMA) submicron particles were prepared using emulsifier-free emulsion polymerization by varying the concentration of the fluorescent comonomer, i.e., NMA. Composition of the particles was characterized by 1H NMR, FT-IR, GPC, and DSC analyses. The molecular weights and particle size of the particles were dependent on the NMA concentration. Second, Fe3O4 nanoparticles were immobilized onto the poly(St/MAA/NMA) submicron particles to give rise to multifunctional properties. The morphology and particles size were characterized by FE-SEM and CHDF. These poly(St/MAA/NMA)/Fe3O4 composite particles exhibited both fluorescent properties under UV irradiation at 365 nm and magnetic properties. Photo-luminescent (PL) intensity of the particles showed linear dependence with NMA concentration.
Keywords: Multifunctional; Monodisperse; Fluorescent; Magnetic; Composite particles; Emulsifier-free polymerization;

Organic capsules have been fabricated via three steps, by using the polymerizable gemini surfactant. Capture and release capabilities of glucose into/from the capsules have also been characterized.Organic capsules have been fabricated via three steps, by using the polymerizable gemini surfactant (1,2-bis(dimethyl(11-methacryloyloxy)undecylammonio) hexane dibromide, PC11-6-11) as a single wall component. In the first fabrication step, the surfactant spontaneously adsorbs on acid-dissolvable melamine formaldehyde (MF) particles in aqueous media. The adsorption isotherm data reveal that the adsorbed amount of PC11-6-11 (per chain) is greater than that of the corresponding monomeric surfactant ((11-methacryloyloxy)undecyltrimethylammonium bromide, PC11), resulting from the greater intermolecular association of PC11-6-11 at the solid/solution interface. The closely packed adsorbed layer of PC11-6-11 provides an opportunity to give a polymer thin film, as a result of in situ photo-polymerization on MF particles (in the second fabrication step) and subsequent acid dissolution of the core MF particles (in the third fabrication step). The dynamic light scattering (DLS) measurements have shown that the apparent hydrodynamic diameter of PC11-6-11 capsules is reversibly changed in response to a change in ionic strength: the increased background electrolyte concentration results in deswelling of the capsules, and vice versa. It seems likely that this swelling/deswelling behavior is primarily driven by the electrostatic interaction between quaternary ammonium groups within the polymerized film. We have also studied the capture and release capabilities of glucose into/from the capsule core and found that (i) glucose is encapsulated into the capsule core at high electrolyte concentrations and (ii) the glucose molecules encapsulated into the core are gradually released when the outer electrolyte solution is replaced by pure water. We believe, therefore, that the PC11-6-11 capsules fabricated here are useful as stimulus-responsive smart vehicles.
Keywords: Gemini surfactant; Polymerizable surfactant; Adsorption; Polymerization; Capsule; Stimulus-responsive nature;

Water-in-oil to bicontinuous to oil-in-water structural transitions in the U-type microemulsions formulated using biocompatible mixed nonionic surfactants and peppermint oil were characterized by the study of the transport, diffusion and microstructure parameters.Water/sucrose laurate/ethoxylated mono-di-glyceride/ethanol/peppermint oil microemulsion systems were formulated and characterized using electrical conductivity, dynamic viscosity, nuclear magnetic resonance, dynamic light scattering, small angle X-ray scattering and cryogenic transmission electron microscopy. The solubilization capacity of water in the oil is dependent on the surfactants and ethanol/oil mixing ratios (w/w). Static percolation phenomena were observed in these systems, and the water volume fraction percolation threshold was determined. A progressive transformation of the water-in-oil to bicontinuous and inversion to oil-in-water microemulsions occurs upon dilution with water, which was revealed by the determination of the diffusion coefficients of both oil and water inside the microemulsions. The diffusion coefficients of the surfactants at the interface of the microemulsions increase with increasing water volume fraction. The periodicity of the microemulsions increases linearly with increasing water volume fraction. In addition, the correlation length increases with water volume fraction to a certain value then decreases. Cryo-TEM images of the oil-in-water microemulsions revealed the presence of spheroidal droplets of up to 12 nm diameter.
Keywords: Percolation threshold; Diffusion coefficients; Hydrodynamic radius; Periodicity; Correlation length;

A micelle to vesicle transition induced by sodium 4-[(E)-phenyldiazenyl] benzoate (AZONa) in 20 mM cetyltrimethylammonium bromide (CTAB) aqueous solution at 50 °C.A photo-responsive azobenzene dye, sodium 4-[(E)-phenyldiazenyl] benzoate (AZONa), was employed to induce microstructural changes with cetyltrimethylammonium bromide (CTAB) in aqueous solution. A spherical micelle to vesicle transition via wormlike micelles was investigated by employing turbidity, viscosity, and dynamic light scattering measurements, as well as cryo-transmission electronic microscopy. At a certain molar ratio [AZONa]/[CTAB] of 0.65 the zero-shear viscosity achieve a maximum, showing clearly the formation of wormlike micelles that obey the classic Maxwellian behavior at low shear frequencies. At this critical molar ratio, an increase in temperature resulted in the breakdown of wormlike micelles, whereas the viscosity η 0 showed three domains of growth characterized by scaling laws as the surfactant concentration was varied between 10 and 40 mM. The rapid increase in η 0 could be explained by an incomplete screening of electrostatic repulsions of the solution. The decrease in η 0 was due to the formation of branched wormlike micelles above once a concentration [CTAB] = 20 mM.
Keywords: Cetyltrimethylammonium bromide; Sodium 4-[(E)-phenyldiazenyl] benzoate; Wormlike micelle; Vesicle; Viscosity; Dynamic light scattering; Cryo-transmission electronic microscopy;

A probabilistic approach to water–water hydrogen bonding is used to examine the temperature effect on the solvent-mediated interaction of two hydrophobic particles immersed in water.Recently, we have proposed a probabilistic approach to examine the effect of water–water hydrogen bond networks around two foreign hydrophobic particles (immersed in water) on their interaction. Because of the proximity to a particle, a water molecule in the first hydration shell around it forms a smaller number of hydrogen bonds compared to a bulk molecule. The probabilistic approach allows one to analytically evaluate the former number if the latter is known (which is usually the case). On the other hand, the former bonds may be slightly (energetically) enhanced compared to the latter if at least one of the two bonded molecules lie in the first hydration shell and does not form a bond with a nearest neighbor site on the particle surface. When two hydrophobic particles are sufficiently close to each other, the overlap of boundary water–water hydrogen bond networks gives rise to an additional attractive force between them. In this paper we use the probabilistic approach to examine the effect of solvent temperature on the solvent-mediated interaction of two hydrophobic particles. Their hydrophobic attraction is affected by the solvent (water) temperature because the density of the solvent, strength of a hydrogen bonds, and number of hydrogen bonds per molecule are sensitive thereto (the pressure effects are not considered here). The probabilistic approach predicts that the solvent-mediated attraction of hydrophobic solutes is driven by the favorable entropic component (“−temperature  ×  entropy”) of the potential of mean force that dominates the unfavorable energetic component. This attraction decreases as the temperature increases.
Keywords: Hydrogen bonding; Hydrophobic interactions; Temperature effects; Entropy of hydrophobic attraction; Energy of hydrophobic attraction;

Influence of ferric oxide modification on the properties of copper oxide supported on γ-alumina by Yong Wu; Fei Gao; Bin Liu; Yue Dai; Haiyang Zhu; Binhua Zhou; Yuhai Hu; Lin Dong; Zheng Hu (522-528).
The dispersed copper oxide and ferric oxide locate in the different layers of the preferentially exposed (1 1 0) plane of γ-Al2O3.X-ray diffraction (XRD), Mössbauer spectroscopy, and temperature-programmed reduction (TPR) were employed to investigate the dispersion and reduction behaviors of the Fe2O3/CuO/γ-Al2O3 system. The results indicated that: (1) the crystalline CuO particle in the CuO/γ-Al2O3 samples was redispersed during impregnating CuO/γ-Al2O3 samples with Fe(NO3)3 solutions; (2) two different dispersion states of surface iron species could be observed, i.e., State I corresponding to the iron(III) species located in the D layer on the surface of γ-Al2O3 and State II corresponding to those in the C layer. The dispersed states of surface iron(III) species were closely related to the iron loading amount; (3) the copper species located in the D layer of alumina surface was easily reduced and the copper species located in the C layer were more stable, which could be due to the influence of the iron(III) species in the different layers; (4) in the NO + CO reaction, the catalytic performances were enhanced due to the Cu–Fe synergism and the main active species in this system should be the surface-dispersed copper oxide species.
Keywords: Incorporation model; Mössbauer spectroscopy; Fe2O3/CuO/γ-Al2O3; NO + CO;

Adhesion force between cyclopentane hydrates and solid surface materials by G. Aspenes; L.E. Dieker; Z.M. Aman; S. Høiland; A.K. Sum; C.A. Koh; E.D. Sloan (529-536).
Adhesion force between cyclopentane hydrates and solid surfaces depends on the initial solid surface energy of different materials and the presence of water and acids in the system.The mechanisms by which hydrates deposit in a petroleum production line are related to pipeline surface properties, fluid composition and properties, and water cut. In this work, adhesion forces between cyclopentane hydrates and solid surfaces were investigated as a function of the solid material, the presence of water and the presence of petroleum acids in the oil phase. The influence of dissolved water on hydrate adhesion forces was also investigated.The results show that the adhesion force between hydrates and solid surfaces was dependent on the surface material; solids with low surface free energy lead to the lowest adhesion forces. The adhesion force was strongly dependent on the presence of water in the system. When a water drop was deposited on the solid surface, the adhesion force between the hydrate and the solid surface was more than 10 times larger than hydrate–hydrate adhesion forces. The presence of a water-saturated oil phase also led to an increase in adhesion force between hydrate particles. Adhesion forces were highest when the solid surfaces are water-wet. Addition of petroleum acids to the oil phase drastically reduced adhesion forces.
Keywords: Hydrate; Deposition; Adhesion; Surface free energy; Petroleum acids; Solid surfaces;

Photochemical synthesis of silver particles using water-in-ionic liquid microemulsions in high-pressure CO2 by Masafumi Harada; Chika Kawasaki; Kenji Saijo; Masashi Demizu; Yoshifumi Kimura (537-545).
The formation process of Ag particles with 4–8 nm in diameter in water-in-[OMIm][BF4] microemulsions in the presence of Tween 20 is monitored by in situ SAXS measurements.Silver particles (Ag particles) were synthesized by the photoreduction of silver perchlorate (AgClO4) in water-in-ionic liquid (IL) microemulsions consisting of nonionic surfactant Tween 20, water, and ionic liquids, [1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm][BF4]) or 1-octyl-3-methylimidazolium tetrafluoroborate ([OMIm][BF4])], mixed with a high-pressure (25 MPa) CO2. The time evolution of the Ag particle formation by photoreduction was investigated by UV–Vis, cryo-TEM, extended X-ray absorption fine structure (EXAFS), and small-angle X-ray scattering (SAXS) measurements. In the particle formation process, aggregation and precipitation of Ag particles were suppressed under high-pressure CO2. The average diameters of the metallic Ag particles prepared in water-in-[BMIm][BF4] and water-in-[OMIm][BF4] microemulsions were estimated from TEM to be 3.2 and 3.7 nm, respectively. SAXS analysis shows that the average diameters of the water droplets, which consisted of ionic precursors of AgClO4 and Ag particles (or Ag aggregates), were estimated to be about 30–40 nm. In the process of Ag particle formation, the water droplet size under high-pressure CO2 is more effectively regulated than that under ambient air, thereby preventing Ag particles from aggregating and precipitating.
Keywords: Ionic liquids; Water-in-ionic liquid microemulsions; Supercritical carbon dioxide; Silver particles; Photoreduction; Cryo-TEM; EXAFS; SAXS;

Competitive adsorption of oleate and silicate onto magnetite surface studied by ATR-FTIR. It was found that silicate modified magnetite surface effectively reduced the adsorption of oleate from aqueous solution.Attenuated Total Reflection (ATR) IR spectroscopy was utilized to monitor adsorption of sodium oleate and sodium silicate onto synthetic magnetite at pH = 8.5, both individually and in a competitive manner. Oleate was adsorbed within a concentration range of 0.01–0.5 mM. It was observed that adsorption of oleate increased linearly with increasing concentration of oleate in solution up to a concentration of 0.1 mM. The infrared spectrum of oleate showed a broad single band at 1535 cm−1 assigned to the asymmetric stretching vibration of carboxylate, implying chemisorption of oleate to the magnetite surface. The kinetics of oleate adsorption followed a pseudo first-order reaction with an apparent rate constant of k 1  = 0.030 ± 0.002 min−1. Competitve adsorption of silicate and oleate was performed either by adding silicate solution to a magnetite film initially equilibrated with 0.1 mM oleate or adding oleate solution to magnetite treated with silicate solutions in the concentration range 0.1–5 mM. It was shown that silicate, within reasonable time, had only minor effect on the amount of oleate already adsorbed on magnetite. On the other hand, oleate did not efficiently compete with silicate if the latter substance was already adsorbed on the iron oxide.
Keywords: ATR-FTIR spectroscopy; Magnetite; Oleate; Silicate; Depressive effect; Adsorption kinetics;

Effects of initial supersaturation on spontaneous precipitation of calcium carbonate in the presence of charged poly-l-amino acids by Branka Njegić-Džakula; Giuseppe Falini; Ljerka Brečević; Željko Skoko; Damir Kralj (553-563).
A model of interactions between dissolved macromolecular additives and different solid phases that may nucleate and grow simultaneously in the precipitation system.Spontaneous precipitation of calcium carbonate was investigated in two precipitation systems: (1) with initial supersaturation lower than that corresponding to the solubility of amorphous calcium carbonate (ACC), at which vaterite precipitated, and (2) with initial supersaturation higher than that of ACC solubility, at which a mixture of calcite and vaterite was formed. After the addition of an acidic polypeptide, poly-l-glutamic acid (pGlu) or poly-l-aspartic acid (pAsp), into (1) a significant inhibition of nucleation, expressed as an increase in induction time, and growth of vaterite, perceived as a dead zone, was observed. Extent of inhibition decreased in the order: Inh pAps  >  Inh pGlu  ≫  Inh pLys. The addition of a polypeptide into (2) caused the inhibition of precipitation and changed the morphology and polymorphic composition of the precipitate; only vaterite appeared at approximately c pAsp  = 3 ppm, c pGlu  = 6 ppm, or c pLys  = 7 ppm. This finding is explained as a consequence of kinetic constraints through the inhibition of calcite nucleation and stronger binding of acidic polypeptide by the calcite surfaces than by the vaterite surfaces. Laboratory precipitation studies using conditions that resemble those in living organism should be run at an initial supersaturation corresponding to the solubility of ACC as a limiting condition.
Keywords: Calcium carbonate; Calcite; Vaterite; Amorphous calcium carbonate; Spontaneous precipitation; Acidic poly-l-amino acids;

Electric permittivity of concentrated suspensions of elongated goethite particles by R.A. Rica; M.L. Jiménez; A.V. Delgado (564-573).
The electric permittivity of elongated goethite particles shows two alpha relaxations when corrected for electrode polarization (EP). Two models are used to fit the data.This paper describes an investigation on the electric permittivity of concentrated suspensions of non-spherical particles, specifically prolate spheroids. It is first discussed how the determination of the frequency (ω) dependence of the electric permittivity (a phenomenon traditionally known as LFDD or low-frequency dielectric dispersion) can provide ample information on the properties of the dispersed material (shape, size, state of aggregation, conductivity) and of its interface with the (typically aqueous) medium. The basic quantities are the strength and frequency dependence of the dipole moment induced by the applied field, and its dimensionless counterpart, the dipole coefficient, C (ω). It is explicitly shown how the (complex) relative permittivity of the suspension, ε r ∗ ( ω ) , can be calculated from it. Two theoretical models on the polarizability of spheroidal colloidal particles will be used as theoretical starting point; one of them (Model I) explicitly considers two relaxations of the permittivity, each associated to one of the particle axes. The other (Model II) is a semi-analytical theory that yields an LFDD practically independent of the axial ratio of the particles. Both models are aimed to be used if the suspensions are dilute (low volume fraction of solids, ϕ ), and here they are generalized to concentrated systems by means of a previously published approximate evaluation of the permittivity of concentrated suspensions. Experiments are performed in the 1 kHz–1 MHz frequency range on suspensions of elongated goethite particles; the effects of ionic strength, pH, and volume fraction are investigated, and the two models are fitted to the data. In reality, taking into account that the particles are non-uniformly charged (a fact that contributes to their instability), two zeta potentials (roughly representing the lateral surface and the tip of the spheroid) are used as parameters. The results indicate that, when experimental conditions are optimal (high ionic strength and low zeta potential), the suspensions do indeed display two relaxations, that we ascribe to the long axis (and to flocs likely present in suspension) and to the short one. The permittivity increases with ionic strength, a result found with other systems, and compatible with a zeta potential that, on the average, decreases with ionic strength, an equally well known result, consequence of electric double layer compression. Another reasonable finding is the increase of estimated average dimensions and the decrease of electrokinetic potentials when the pH is close to the isoelectric point of goethite (around pH 9). The increase in volume fraction, finally, produces an overall increase in the permittivity, and the approximate model used for the evaluation of volume fraction variations can describe properly these effects, with basically constant zeta potentials and dimensions.
Keywords: Alpha relaxation; Concentrated suspensions; Electric permittivity; Electrokinetics; Goethite; Spheroidal particles;

Hysteresis during contact angles measurement by M. Elena Diaz; Javier Fuentes; Ramon L. Cerro; Michael D. Savage (574-583).
When a drop is first placed on top of a solid surface, there is no adsorbed film in contact with the vapor/liquid interface. By a process of evaporation/adsorption, an adsorbed film grows and modifies the mechanical equilibrium and the apparent contact angle.A theory, based on the presence of an adsorbed film in the vicinity of the triple contact line, provides a molecular interpretation of intrinsic hysteresis during the measurement of static contact angles. Static contact angles are measured by placing a sessile drop on top of a flat solid surface. If the solid surface has not been previously in contact with a vapor phase saturated with the molecules of the liquid phase, the solid surface is free of adsorbed liquid molecules. In the absence of an adsorbed film, molecular forces configure an advancing contact angle larger than the static contact angle. After some time, due to an evaporation/adsorption process, the interface of the drop coexists with an adsorbed film of liquid molecules as part of the equilibrium configuration, denoted as the static contact angle. This equilibrium configuration is metastable because the droplet has a larger vapor pressure than the surrounding flat film. As the drop evaporates, the vapor/liquid interface contracts and the apparent contact line moves towards the center of the drop. During this process, the film left behind is thicker than the adsorbed film and molecular attraction results in a receding contact angle, smaller than the equilibrium contact angle.
Keywords: Contact angle; Intrinsic hysteresis; Molecular forces; Advancing;

Thin liquid film drainage: Ionic vs. non-ionic surfactants by Stoyan I. Karakashev; Dilyana S. Ivanova (584-593).
Thin liquid film in cylindrical coordinate system.This paper compares the rate of drainage of thin liquid films (TLF) containing ionic surfactants to that of TLF containing non-ionic surfactants.In essence, the theory of drainage has been developed for films containing non-ionic surfactants, while the validation of the models, based on the theory in the literature, has been performed with experiments on TLF with both, non-ionic and ionic surfactants, usually in the presence of significant background concentrations of electrolyte.Due to the complexity of problem, the dynamic effects on the electrical double layer (EDL) during the film drainage have been ignored for many years in the literature. These effects were finally treated theoretically and the problem solved numerically in a recent work. The new theoretical development however has not yet been validated. In addition, the differences in the kinetics of thinning of TLF with ionic and non-ionic surfactants have not been exposed in the literature until present. This paper is dedicated to revealing these differences.Experiments on kinetics of thinning were conducted with microscopic planar TLF, containing two non-ionic surfactants (tetraethyleneglycol mono-octylether C8E4 and n-dodecyl--d-maltoside C12G2) and two ionic surfactants (sodium dodecylsulfate SDS and tetrapentylammonium bromide TPeAB).The TLF with non-ionic surfactants drain according to the well-known theories of Scheludko or Radoev-Manev–Ivanov, which confirms their validity. On the contrary, TLFs with ionic surfactants drain in general at significantly slower rate, as compared to the TLF with non-ionic surfactants, when far from equilibrium. When they are close to the equilibrium conditions, the former drain according to the theory developed for TLF with non-ionic surfactants.An analysis of the experimental results, involving the latest achievements in the field is performed, indicating the complex behaviour of the electrical double layer under dynamic conditions.
Keywords: Foam film drainage; Thin liquid films; Electrical double layer; Ionic surfactants; Non-ionic surfactants;

Comparison of the contact angle for aqueous solution of TX-100 and TX-165 with short chain alcohols mixtures on the quartz surface at the solution surface tension equal to 33 mN/m.Measurements of advancing contact angles for aqueous solution of Triton X-100 (TX-100) with methanol, ethanol and propanol mixtures and Triton X-165 (TX-165) with the same alcohols on quartz surface were carried out. From the obtained results it appeared that the wettability of quartz depends on Triton’s and alcohol concentrations and that there is a linear dependence between the adhesional and surface tension of aqueous solution of Triton’s and alcohols mixtures. This dependence can be described by linear equations which constants depend somewhat on the Triton’s and alchohols concentration. The slope of all linear dependencies between the adhesional and surface tension is positive. The critical surface tension of quartz wetting determined from these dependencies by extrapolating the adhesional tension to a value equal to the surface tension (for contact angle equal zero) depends on the assumption whether the concentration of Triton or alcohols was constant. The average value at constant Triton’s concentration was equal to 27.1 mN/m and was lower than that evaluated at constant alcohol concentration (29.5 mN/m). The critical surface tension of quartz wetting at constant alcohol concentration was nearly the same as the apolar component of the surface tension of quartz covered with water monolayer film. The positive slope of the adhesional-surface tension curves and the work of water adhesion, Triton’s and alcohols to quartz surface indicates that the interaction between water molecules and quartz surface might be stronger than that between quartz and surface active agents molecules. So, the concentration excess of surfactants at quartz–water interface is probably negative, and the possibility of the surface active agents to adsorb at quartz/water film–water interface is higher than that at the quartz–water. However, at alcohol concentration above that of its aggregation the molecules of the surface active agents probably destroy the strongly ordered film of water.
Keywords: Quartz; Surfactants; Alcohols; Adsorption; Surface tension; Adhesion work;

On the mechanism of patterning in rapidly evaporated polymer solutions: Is temperature-gradient-driven Marangoni instability responsible for the large-scale patterning? by Edward Bormashenko; Sagi Balter; Roman Pogreb; Yelena Bormashenko; Oleg Gendelman; Doron Aurbach (602-607).
Large-scale pattern observed under evaporation of the polymer solution.Large-scale self-organization occurring on the scale of dozens of micrometers in rapidly evaporated polymer solutions based on amorphous polymers and chlorinated solvents was studied. Heating the substrate from below destroys the patterning. This contradicts the idea that self-organization is due to the jump in surface tension caused by a temperature gradient (temperature-gradient-driven Marangoni instability). We relate the patterning to the concentration-gradient- driven effects.
Keywords: Patterning; Polymer solution; Evaporation; Marangoni instability; Surface tension; Repulsive/attractive interface;

The electropolymerization of a new perfluoroalkyl alkyl pyrrole lead to surfaces that exhibit a sticky superhydrophobicity not only in pure water but also in corrosive solutions such as acids and bases.Over the past few years, electropolymerization of semifluorinated monomers like thiophene or pyrrole has been used as a gentle and effective method to generate, in one step, stable superhydrophobic surfaces. The synthetic route mostly involves the coupling reaction between a carboxylic acid and an alcohol, using a carboxy group-activated reagent and a catalyst. As a consequence, the electroformed surfaces present high liquid repellency due to the concomitant effect of roughness and low surface energy. Nevertheless, the ester connector can be cleaved under acidic and basic conditions, preventing its use under a range of environmental conditions. To overcome this drawback, a new perfluoroalkyl alkyl pyrrole has been synthesized, the fluorinated segment being connected to the electropolymerizable part via an alkyl chain, and electropolymerized, leading to surfaces that exhibit a static contact angle with water superior to 150° and no sliding angle, over a wide pH range and with a long lifetime. This represents the first example of a pure conducting polymer surface with sticky superhydrophobicity not only in pure water but also in corrosive solutions such as acids and bases, giving rise to new prospects in practical applications.
Keywords: Conjugated polymers; Electropolymerization; Fluoropolymers; Acid and alkaline superhydrophobicity; Sticky surfaces; Anticorrosion;

SBA-15 mesoporous materials grafted with mono-, di- and triammonium organic functional groups proved to be potent adsorbents for the removal of monobasic phosphate ( H 2 PO 4 - ) anions from aqueous solutions even at high concentrations. The synthesized materials demonstrated high adsorption capacities reaching 2.46 mmol H 2 PO 4 - /g adsorbent.Adsorption of monovalent phosphate anions from aqueous solutions on mono, di- and tri-ammonium-functionalized mesoporous SBA-15 silica was investigated. The adsorbent was prepared via a post-synthesis grafting method, using 3-aminopropyltrimethoxysilane (N-silane), [1-(2-aminoethyl)-3-aminopropyl]trimethoxysilane (NN-silane) and 1-[3-(trimethoxysilyl)-propyl]-diethylenetriamine (NNN-silane), followed by acidification in HCl solution to convert the attached surface amino groups to positively charged ammonium moieties. The loading of amino moieties on the SBA-15 surface was varied from 5% to 40% as organoalkoxysilane/silica molar ratio. The adsorption experiments were conducted batchwise at room temperature. Results showed that adsorption capacity increased with increasing the concentration of functional groups on the SBA-15 adsorbent whatever the nature of the functional group. In the case of monoammonium functional groups, the adsorption capacity increased from 0.64 to 1.07 mmol H 2 PO 4 - /g when the molar ratio organoalkoxysilane/silica was varied from 5% to 40%, respectively. Similar tendency was observed in the case of diammonium and triammonium organic functional groups. Also, for the same organoalkoxysilane/silica molar ratio, the adsorption capacity increased markedly with the increase of the number of protonated amines in the functional groups. Therefore, maximum adsorption capacities of 1.07, 1.70 and 2.46 mmol H 2 PO 4 - /g adsorbent were obtained using mono-, di- and tri-ammonium-functionalized SBA-15, respectively.
Keywords: Adsorption; Phosphate; Mesoporous silica; Ammonium-functionalized SBA-15;

Nanoporous polymer – Clay hybrid membranes for gas separation by Guillaume Defontaine; Anne Barichard; Sadok Letaief; Chaoyang Feng; Takeshi Matsuura; Christian Detellier (622-627).
Nanohybrid organo-inorgano clay mineral-polydimethylsiloxane (PDMS) membranes, with PDMS chains covalently linked to sepiolite microfibers, were synthesized, characterized and tested for the separation of CO2/CH4 and O2/N2 mixtures.Nanohybrid organo–inorgano clay mineral-polydimethylsiloxane (PDMS) membranes were prepared by the reaction of pure and/or modified natural clay minerals (Sepiolite and montmorillonite) with PDMS in hexane, followed by evaporation of the solvent at 70 °C. The membranes were characterized by means of XRD, SEM, ATD-TG and solid state 29Si magic angle spinning (MAS) and cross-polarization (CP) CP/MAS NMR. The morphology of the membranes depends on the content loading of clay mineral. For low content, the membrane composition is homogeneous, with well dispersed nanoparticles of clay into the polymer matrix, whereas for higher clay content, the membranes are constituted also of a mixture of well dispersed nanoparticles into the polymer, but in the presence of agglomerations of small clay particles. Quantitative 29Si MAS NMR demonstrated a strong correlation between the clay content of the membrane and the average length of the PDMS chain, indicating that the nanohybrid material is made of clay particles covalently linked to the PDMS structure. This is particularly the case for Sepiolite with has a high density of Q2 silanol sites. The separation performances of the prepared membranes were tested for CO2/CH4 and O2/N2 mixtures. The observed separation factors showed an increase of the selectivity in the case of CO2/CH4 in comparison with membranes made from PDMS alone under the same conditions.
Keywords: Separation membranes; Inorganic membranes; Polydimethylsiloxane; Clay minerals; Sepiolite; Montmorillonite; Si-29 MAS NMR; Nanohybrid materials; Thermal gravimetric analysis; Scanning electron microscopy;

Our technique enables to distinguish ternary lipid mixture into several clusters with similar membrane properties. The results should contribute to elucidating lipid domain formation.A novel method for investigating phase behavior in a ternary lipid membrane was developed and tested. Sixty-five model membranes composed of sphingomyelin (SM), dioleoyl phosphatidylcholine (DOPC), and cholesterol (Ch) were prepared, and fluorescence anisotropy between 25 °C and 60 °C was measured. Observed fluorescence anisotropy curves as functions of temperature were analyzed using a nonlinear response surface method and Kohonen’s self-organizing map. Thus, we generated a scatter plot indicating the distribution of membranes with similar membrane properties. The scatter plot showed that the SM/DOPC/Ch membranes resolved into six clusters with distinct membrane properties. We then conducted differential scanning calorimeter (DSC) measurement of membranes typical of the clusters. The results indicated that the membranes consisted of several phase domains (i.e., Lα , Lβ , lo phase domains), and the clusters were distinguished by differences in the type and content of membrane domain. This method is accurate because the clusters were determined based on experimental values. This technique is useful for elucidating the phase behavior of ternary lipid membranes. These findings contribute to clarification of domain formation.
Keywords: Lipid raft; Liposome; Fluorescence anisotropy; Response surface method; Kohonen’s self-organizing map; Clustering;

by Arthur Hubbard (634).