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Journal of Colloid And Interface Science (v.304, #2)

Editorial Board (pp. co1).

A new glance at ruthenium sorption mechanism on hydroxy, carbonate, and fluor apatites: Analytical and structural studies by K. Tõnsuaadu; M. Gruselle; F. Villain; R. Thouvenot; M. Peld; V. Mikli; R. Traksmaa; P. Gredin; X. Carrier; L. Salles (pp. 283-291).
The sorption mechanism of Ru3+ ions on hydroxy (HAp), carbonate (CO3HAp), and fluor apatites (FAp) has been studied in detail. Ru apatites were obtained by reaction of the apatites with RuCl3 in aqueous solution. The structure and composition of the ruthenium-modified apatites were studied by several techniques: elemental analysis, XRD, EXAFS, IR, NMR, SEM-EDS, TEM, and thermal analysis. The amount of Ru in the modified apatite varies from 7.8 to 10.5 wt% and is not related to the initial composition or the specific surface area of the apatite. The different characterization techniques show that in the Ru-modified apatites Ru is surrounded by six oxygen atoms and do not contain any chlorine. For Ru-HAp and Ru-CO3HAp the new phase is amorphous whereas it is crystalline for FAp. The catalytic oxidation ability is higher for Ru-HAp and Ru-CO3HAp compared to Ru-FAp apatite in the oxidation of benzylic alcohol.Reaction of RuCl3 with calcium apatites leads to the formation of a new rich Ru phase, whose crystallinity depends on the nature of the starting apatite.

Keywords: Ruthenium catalyst; Hydroxy apatite; Fluor apatite; Structure; Chemical composition; Catalytic activity

Layered double hydroxides as potential chromate scavengers by Srinivasa V. Prasanna; R. Anantha Padmanabha Rao; P. Vishnu Kamath (pp. 292-299).
The LDH of Ni with Fe, having the formula Ni1− xFe x(OH)2(A n) x/ nyH2O (A=NO3, Cl;x=0.25, 0.33), scavenges CrO2−4 ions from solution throughout the concentration range examined (0.00625–0.25 N). The CrO2−4 uptake capacity is independent of the anion in the starting LDH but is higher whenx=0.25 (3.60 meq g−1) as compared tox=0.33 (2.40 meq g−1). These values are higher than those observed for control compounds β-Ni(OH)2 (1.86 meq g−1) and FeO(OH) (1.26 meq g−1), which do not have any interlayer chemistry, showing that chromate uptake takes place by its incorporation in the interlayer region by a stoichiometric anion-exchange reaction, rather than by adsorption. Nevertheless, the interaction between the LDH and the chromate ions is weak. The weak interaction is due to the mismatch between the symmetry of the chromate ions and the symmetry of the interlayer site, which introduces turbostratic disorder in the chromate-intercalated LDHs. The chromate ions can be completely leached out by soaking the LDH in a sodium carbonate solution.The layered double hydroxides of Ni with Fe exhibit aggressive chromate uptake from solution. The interaction is however weak and the entire chromate can be leached out in a sodium carbonate solution paving the way for chromate recovery.

Keywords: Layered double hydroxides; Chromate uptake; Anion exchange

Simultaneous removal of ammonium and phosphate by zeolite synthesized from fly ash as influenced by salt treatment by Deyi Wu; Baohua Zhang; Chunjie Li; Zhenjia Zhang; Hainan Kong (pp. 300-306).
To develop an effective technique for enhancing the removal efficiency of ammonium and phosphate at low concentrations without losing potential removal capacity, Na-ZFA (zeolite synthesized from fly ash) was converted into Ca-, Mg-, Al-, and Fe-ZFA by salt treatment and the simultaneous removal of ammonium and phosphate by ZFA saturated with different cations was investigated. It was shown that Al3+-ZFA had the highest removal efficiencies (80–98%) for ammonium, followed by Mg2+ (43–58%), Ca2+ (40–54%), Na+ (<20%), and Fe3+ (<1%). Both alkaline pH values (in the cases of Na+, Ca2+, Mg2+) and acidic pH value (in the case of Fe3+) inhibited the sequestration of ammonium. At low initial phosphate concentrations, the efficiency of phosphate removal by Al3+- and Fe3+-ZFA approached 100%, followed by Ca2+ (60–85%), Na+ (<25%), and Mg2+ (<5%). The difference in phosphate removal efficiency was explained by the adsorption mechanisms. It was concluded that ZFA could be used in simultaneous removal of NH+4 and phosphate at low concentrations with presaturation by an appropriate cation such as Al3+ through salt treatment.Salt treatment could efficiently improve the ability of ZFA (zeolite synthesized from fly ash) to simultaneously sequestrate ammonium and phosphate at low concentrations from wastewater. The figure shows the case of ammonium removal.

Keywords: Ammonium; Phosphate; Simultaneous removal; Low concentration; ZFA

The adsorption behavior of crystal violet in functionalized sporopollenin-mediated column arrangements by Orhan Gezici; Muhittin Küçükosmanoğlu; Ahmet Ayar (pp. 307-316).
The adsorption behavior of Crystal Violet (CV) on a sporopollenin-based solid phase, carboxylated diaminoethane sporopollenin (CDAE-S), was investigated under column conditions, and the obtained breakthrough profiles were used in evaluations and quantifications. The adsorption capacity of the CDAE-S was observed to be considerably higher than that of diaminoethane sporopollenin (DAE-S), revealing the importance of electrostatic interactions and carboxyl groups in the adsorption of CV on the CDAE-S. The binding of CV on the DAE-S was found to be a typical nonspecific adsorption, whilst cation-exchange was proposed as the main mechanism for monolayer adsorption of CV on the CDAE-S. Hence in the present study, the cation-exchange is suggested as an effective process for removal and recovery of CV from aqueous effluents, and in view of the pH point of zero charge matter, multifunctionality of the CDAE-S is discussed in detail, and various application possibilities based on “aminocarboxylic acid? functionality are also drawn.In the present study, a sporopollenin-based material, carboxylated diaminoethane sporopollenin (CDAE-S), is proposed as a multifunctional solid phase for removal of dyes.

Keywords: Adsorption isotherm; Breakthrough curve; Dye; Ion-exchange; Point of zero charge; Scatchard plot analysis; Solid-phase extraction

Adsorption studies of arsenic on Mn-substituted iron oxyhydroxide by P. Lakshmipathiraj; B.R.V. Narasimhan; S. Prabhakar; G. Bhaskar Raju (pp. 317-322).
Mn-substituted iron oxyhydroxide (Mn0.13Fe0.87OOH) was prepared by the oxidation of ferrous carbonate precipitated from ferrous sulfate and sodium carbonate solutions. X-ray diffraction analysis led to the conclusion that the sample was basically iron manganese hydroxide with bixbyite structure. The sample exhibited a surface area of 101 m2 g−1 and a pore volume of 0.35 cm3 g−1. Batch experiments were conducted to study the adsorption of arsenite and arsenate species onto Mn-substituted iron oxyhydroxide (MIOH) and adsorption equilibrium time was evaluated. The temperature of adsorption was varied from 30 to 60 °C. The maximum uptake of arsenite and arsenate was found to be 4.58 and 5.72 mg g−1, respectively. Zeta potential measurements and FT-IR spectral studies were also conducted to study the nature of adsorption. In both cases, adsorption was best described by Langmuir isotherm and activation energies as calculated from a model-free isoconversional method were found to be on the order of 15–24 and 45–67 kJ mol−1 for arsenate and arsenite, respectively.The degree of adsorption against time shows that the kinetics of adsorption of arsenate is faster than that of arsenite. The uptake of arsenite is markedly enhanced at higher temperature.

Keywords: Mn-substituted ferric oxide; Langmuir isotherm; Adsorption kinetics; Isoconversion; Arsenite; Arsenate; Activation energy

Decoration carbon nanotubes with Pd and Ru nanocrystals via an inorganic reaction route in supercritical carbon dioxide–methanol solution by Zhenyu Sun; Zhimin Liu; Buxing Han; Shiding Miao; Zhenjiang Miao; Guimin An (pp. 323-328).
This work describes a method to decorate carbon nanotubes (CNTs) with metallic Pd and Ru nanocrystals via inorganic reactions in supercritical (SC) CO2–methanol solutions. In this route, PdCl2 or RuCl3⋅3H2O dissolved in SC CO2–methanol solution acted as a metal precursor and CNTs functioned as a template to direct the deposition of produced nanoparticles. Methanol served as the reductant for the precursors as well as cosolvent to enhance the dissolution of precursors in SC CO2. Dry products were readily obtained through in situ extraction with SC CO2 after reactions. The products were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. It was demonstrated that the loading content and particle size of the nanoparticles deposited on CNTs could be tuned by changing the weight ratio of the precursor to CNTs. This simple and efficient approach may also be utilized to synthesize other high-purity materials using inorganic salt precursors in SC CO2-based solution.The metal (Pd, Ru)-carbon nanotube (CNT) nanocomposites have been fabricated in supercritical CO2–methanol solutions using PdCl2 and RuCl3⋅3H2O as a precursor, respectively. The loading content and particle size of the nanoparticles deposited on CNTs could be readily tuned by changing the weight ratio of the precursor to CNTs. This simple and efficient approach may be extended to synthesize other metal–CNT composites, which opens up avenues for further exploration of the properties of CNT-based composites.

Keywords: Carbon nanotubes; Supercritical fluid; Catalysis; Palladium; Ruthenium; Nanocomposites

A control over accessibility of immobilized enzymes through porous coating layer by Kallol Mohanta; Amlan J. Pal; Sangita Roy; Prasanta Kumar Das (pp. 329-334).
We report immobilization of an enzyme by layer-by-layer (LbL) film deposition technique. All the enzyme layers, including the inner ones, contributed to the activity. We put-forwarded additional coating layers to protect the enzymes. To control the accessibility of the enzymes beneath the coating layer, pores have been introduced. Our results show controlled accessibility of immobilized enzymes in solid-state matrices.

Keywords: Layer-by-layer assembly; Immobilization; Enzymes; Horseradish peroxidase

Coupling between polysaccharide gelation and micro-phase separation of globular protein clusters by Karine Baussay; Dominique Durand; Taco Nicolai (pp. 335-341).
The effect of gelation of the polysaccharide phase on the phase separation was investigated for mixtures of anionic polysaccharide ( κ-carrageenan) and globular protein ( β-lactoglobulin) clusters at pH 7 well above the iso-electric point. Gelation of κ-carrageenan was induced by cooling in the presence of KCl. In the liquid state the protein clusters phase-separate into relatively dense micro-domains. When the polysaccharide phase gelled during cooling, the turbidity of the systems decreased dramatically. Light scattering experiments showed that the density of the micro-domains decreased, while microscopy showed that the number and size was not strongly modified. It is concluded that smaller protein clusters leave the micro-domains when κ-carrageenan gels. The effect could be reversed by reheating the samples and thus melting the gel and was observed for repeated heating and cooling cycles. The effect of gelation on phase separation decreases with increasing polysaccharide concentration and with ageing of the liquid mixture. The latter is caused by the formation of bonds between the protein clusters in the micro-domains that slowly reinforce with time.

Keywords: Gel; Phase separation; Protein; Polysaccharide; Rheology; Turbidity

Lysozyme binding onto cat-anionic vesicles by A. Bonincontro; E. Spigone; M. Ruiz Peña; C. Letizia; C. La Mesa (pp. 342-347).
Mixing aqueous sodium dodecylsulfate with cetyltrimethylammonium bromide solutions in mole ratios close to (1.7/1.0) allows the formation of cat-anionic vesicles with an excess of negative charges on the outer surface. The vesicular dispersions are mixed with lysozyme, and interact electrostatically with the positive charges on the protein, forming lipo-plexes. Dielectric relaxation, ζ-potential, and light scattering indicate the occurrence of interactions between vesicles and the protein. According to CD, the vesicle-adsorbed protein retains its native conformation. Binding and surface saturation, inferred by dielectric relaxation and ζ-potential, fulfil a charge neutralisation stoichiometry. Adsorbed lysozyme promotes the vesicle clustering and is concomitant with the lipo-plexes flocculation. Above the charge neutralisation threshold, lysozyme in excess remains dispersed in molecular form. Attempts were made to determine in what conditions protein release from the vesicles occurs. Accordingly, the full neutralisation of sodium dodecylsulfate in excess by cetyltrimethylammonium bromide ensures the lipo-plexes break-up, the precipitation of the mixed surfactants and the protein release in native form.Cat-anionic vesicles made of SDS and CTAB interact with lysozyme. Interactions give rise to vesicle saturation. An investigation based on DLS, dielectric relaxation, CD, and ζ-potential indicates that lipo-plexes are being formed.

Keywords: Cat-anionic vesicles; Protein binding; Protein–vesicle interactions; Lipo-plexes; Surface saturation; DLS; CD; ζ; -Potential; Dielectric relaxation

Role of solvation forces in the gelation of fumed silica–alcohol suspensions by William E. Smith; Charles F. Zukoski (pp. 348-358).
Aggregation and gelation kinetics of fumed silica were investigated by altering the solvent–surface interactions. Native and surface-modified (hydrophobic) fumed silica particles were dispersed in short-chain linear alcohols. Based on the kinetics of aggregation and gelation, we show that the solvent–surface interactions have a tremendous impact on the bulk suspension properties. The gelation kinetics were qualitatively similar in all of the fumed silica–alcohol samples, and the gel times for all the alcohols were captured on a master curve requiring two parameters. The two parameters, the stability ratio and critical volume fraction, describe the two regimes of gelation. At low concentrations, gelation occurs due to aggregation of the particles diffusing over a potential barrier (15–25kT). The rate of aggregation and time to gelation then scales with the stability ratio. At high particle loadings, gelation occurs at a critical volume fraction due to localization in a secondary minimum with a depth of3–4kT. These observations are supported by evidence of hydrogen bonding between the solvent and the particle, creating oscillatory solvation forces that govern the magnitude of these two parameters.Primary and secondary minimum gelation is governed by solvent–surface interactions for fumed silica–alcohol suspensions.

Keywords: Aggregation kinetics; Colloidal gels; Dynamic light scattering; Fumed silica; Mode coupling theory; Solvation forces

Aggregation and gelation kinetics of fumed silica–ethanol suspensions by William E. Smith; Charles F. Zukoski (pp. 359-369).
The kinetics of aggregation and gelation of fumed silica suspended in ethanol were investigated as a function of volume fraction. At low particle concentrations, gelation is well described by aggregation into a primary minimum arising from hydrogen bonding and dispersion forces. The gelation is extremely slow due to an energetic barrier (∼25kT) in the interparticle potential associated with solvation forces. The solvation forces also contribute to the formation of a secondary minimum in the interparticle potential. The depth of this minimum (∼3kT) is sufficient that, at a critical particle concentration, long-range diffusion is arrested due to the short-range attractions and the cooperative nature of particle interactions, as described by mode coupling theory. The presence of the secondary minimum is also observed in the microstructure of the gels studied using X-ray scattering. These observations reinforce the importance of understanding the role of solvent–particle interactions in manipulating suspension properties.Two distinct mechanisms of gelation modified by solvation forces in fumed silica–ethanol suspensions. (1) Diffusion over potential barrier into primary minimum. (2) Localization in a secondary minimum.

Keywords: Aggregation kinetics; Colloidal gels; Dynamic light scattering; Fumed silica; Mode coupling theory; Solvation forces

Monodisperse hollow titania nanospheres prepared using a cationic colloidal template by Tae Hee Kim; Kwang Hee Lee; Yong Ku Kwon (pp. 370-377).
Titania-coated polymeric nanoparticles were synthesized based on the cationic colloidal particles which were prepared by surfactant-free emulsion copolymerization of styrene and butylacrylate in the presence of a cationic monomer, methacryloxyethyltrimethyl ammonium chloride (MOTAC) using azobis(isobutylamidine)hydrochloride (AIBA) as an initiator. These cationic particles were stabilized by poly(vinylpyrrolidone) (PVP). Then, these particles were dispersed in ethanol and mixed with titanium(IV) butoxide. Negatively charged titania precursors were rapidly hydrolyzed onto the cationic surfaces of colloidal particles. Subsequently, the samples were heated to 450 °C to form anatase TiO2 and to remove the colloidal template, which resulted in hollow nanospheres. The hollow titania particles were characterized with zeta analyzer, transmission electron microscopy, scanning electron microscopy, light scattering, X-ray diffraction, thermogravimetric analysis and FT-IR.Titania-coated polymeric nanoparticles were synthesized based on the cationic colloidal particles which were prepared by surfactant-free emulsion copolymerization of styrene and butylacrylate in the presence of a cationic monomer, methacryloxyethyltrimethyl ammonium chloride (MOTAC) using azobis(isobutylamidine hydrochloride) (AIBA) as an initiator. These cationic particles were stabilized by poly(vinylpyrrolidone) (PVP). Then, these particles were dispersed in ethanol and mixed with titanium(IV) butoxide. Negatively charged titania precursors were rapidly hydrolyzed onto the cationic surfaces of colloidal particles. Subsequently, the samples were heated to 450 °C to form anatase TiO2 and to remove the colloidal template, which resulted in hollow nanospheres.

Keywords: Nanoparticles; Hollow titania; Surfactant-free emulsion polymerization; Cationic colloidal template

Effect of pH and hydration on the normal and lateral interaction forces between alumina surfaces by M. Polat; K. Sato; T. Nagaoka; K. Watari (pp. 378-387).
Interaction forces between alumina surfaces were measured using an AFM–colloid probe method at different pHs. For an α-alumina–sapphire system at acidic pH, the force curve exhibited a well-defined repulsive barrier and an attractive minimum. At basic pH, the interactive force was repulsive at all separations with no primary minimum. Lateral force measurements under the same conditions showed that frictional forces were nearly an order of magnitude smaller at basic pH than those observed at acidic pH. This behavior was attributed to the hydration of the alumina surface. Normal and lateral force measurements with the strongly hydrated ?-alumina surfaces supported these findings.Normal forces measured by colloid probe method between alumina surfaces were always repulsive at basic pH where the frictional forces also decreased significantly compared to those observed at acidic pH. Most probable reason is hydration of the surfaces.

Keywords: Atomic force microscopy; Colloid probe; Force curve; DLVO theory

Application of a multi-dentate amphiphilic compound to transfer silver nanoparticles into an organic solvent by Nan Gao; Jinfeng Dong; Hao Zhang; Xiaohai Zhou; Gaoyong Zhang; Julian Eastoe (pp. 388-393).
A multi-dentate amphiphilic compound, 3,3′-(dodecylazanediyl)-bis-[ N-(2-aminoethyl)propanamide] (12C–2NH2) has been synthesized. The molecular structure was characterized by Fourier transform infrared (FT-IR) spectroscopy, ultraviolet–visible (UV–vis) spectra, nuclear magnetic resonance (NMR) spectra, and fast atom bombardment mass (FAB-MS) spectra. 12C–2NH2 was employed to stabilize silver nanoparticles. Surface properties and stability of silver nanoparticles were controlled by adjusting the 12C–2NH2 to silver (0) molar ratio. 12C–2NH2 was also applied to transfer silver nanoparticles from an aqueous to an organic phase. The transfer efficiency depends on 12C–2NH2 concentration. When 12C–2NH2 to silver (0) molar ratio was 2:1, the highest efficiency of phase transfer to toluene was obtained. These 12C–2NH2 stabilized silver nanoparticles are very stable over a period of four days in toluene.3,3′-(dodecylazanediyl)-bis-[ N-(2-aminoethyl)propanamide] was applied to transfer silver nanoparticles from an aqueous to an organic phase. The transfer efficiency depends on its concentration.

Keywords: Multi-dentate; Silver nanoparticles; Phase transfer

Control of the electrical conductivity of composites of antimony doped tin oxide (ATO) nanoparticles and acrylate by grafting of 3-methacryloxypropyltrimethoxysilane (MPS) by Willem Posthumus; Jozua Laven; Gijsbertus de With; Rob van der Linde (pp. 394-401).
The effect of the addition of antimony doped tin oxide (ATO) nanoparticles on the electrical conductivity of acrylate films is described. To enable dispersing of ATO in acrylate matrices, 3-methacryloxypropyltrimethoxysilane (MPS) was grafted on the surface of the filler. The amount of MPS used for this surface modification was found to strongly affect the electrical conductivity. Surface modification with a large amount of MPS resulted in colloidally stable dispersions of ATO, leading to a homogeneous distribution. Surface modification with small amounts of MPS led to instable ATO dispersions and aggregation of ATO into a fractal type network, which gives a much higher conductivity especially at low-volume fractions. For composites with a fractal type ATO network a second effect was found. Decreasing the amount of on ATO grafted MPS resulted in an increase of the electrical conduction between the ATO particles.

Keywords: Nanoparticles; Grafting with methacryloxypropyltrimethoxysilane; Electrical conductivity; Fractal aggregate; Ebecryl 745; PEGDA; TMPTA

Fabrication of CdSe composite by using the amphiphilic block copolymer as template by Zhongli Lei; Xiangyu Wei; Youhua Fan; Yalan Liu; Shuxian Bi (pp. 402-407).
CdSe nanoparticles of improved stability against aggregation were synthesized by using amphiphilic block copolymer polyacrylonitrile- block-poly(ethylene glycol)- block-polyacrylonitrile (PAN- b-PEG- b-PAN, PEA). The products were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopic (HRTEM). The optical properties were characterized by UV–vis spectrophotometer and the room temperature photoluminescence (PL). The results revealed that the CdSe nanoparticles have been uniformly distributed throughout the copolymer with diameters of 6–7 nm and the produced novel hybrid nanocomposites displayed obviously quantum size effects and interesting fluorescence features. FTIR results provided the information on the interaction between the copolymer and the nanoparticles. The TGA revealed that the thermal property of the copolymer enhanced due to the interaction of the nanoparticles and the groups of the copolymer.CdSe nanocomposite consisting of well-dispersed CdSe crystals had been successfully obtained by using the amphiphilic block copolymer PEA as a stabilizer.

Keywords: CdSe; Nanoparticles; Copolymer; Semiconductor

Synthesis of single crystal CdMoO4 octahedral microparticles via microemulsion-mediated route by Qiang Gong; Gang Li; Xuefeng Qian; Hongliang Cao; Weimin Du; Xiaodong Ma (pp. 408-412).
The single crystal octahedra of tetragonal CdMoO4 were synthesized on large scale via a microemulsion-mediated hydrothermal route at 120 °C for 10 h. The structures, compositions and morphologies of the as-prepared products were characterized by X-ray power diffraction pattern, field emission scanning electronic microscopy, transmission electron microscopy. Further studies reveal that the octahedral CdMoO4 crystal has eight equivalent exposed crystal faces{101}. The possible growth mechanism of the CdMoO4 octahedral is based on the anisotropic growth habit of CdMoO4 crystals and the selective absorption of surfactant molecules CTAB on the faces of the prime crystals, and the reaction time, composition of the microemulsions and temperature have considerable effects on the final morphology of CdMoO4.Large scale of monodisperse single crystal CdMoO4 octahedral microparticles has been prepared via a microemulsion-mediated hydrothermal procedure.

Keywords: CdMoO; 4; Octahedral microparticles; Microemulsion-mediated; Hydrothermal

Microwave-assisted synthesis of anhydrous CdS nanoparticles in a water–oil microemulsion by Eugenio Caponetti; Delia Chillura Martino; Maurizio Leone; Lucia Pedone; Maria Luisa Saladino; Valeria Vetri (pp. 413-418).
Microwave irradiation at a frequency of 2.45 GHz and a power ranging between 22 and 30 W was used, in a water–oil microemulsion at35±2°C, to obtain stable, small, crystalline, anhydrous CdS nanoparticles exhibiting enhanced luminescence properties. The process of nanoparticles growth at different irradiation times was followed by UV–vis spectroscopy. It was observed that irradiated nanoparticles grew faster and their size reached a constant value. The final mean nanoparticle diameter was 2.7 nm, smaller than that observed in a non-irradiated sample, in which particle dimensions slowly increased even after 10 h. This finding was confirmed by high resolution transmission electron microscopy which also suggested that the spherical nanoparticles had a narrow size distribution and were spatially well separated. Furthermore, Fourier transform infrared spectroscopy was used to obtain information about structural changes that the microemulsion underwent when irradiated by microwaves. In particular, the evolution of the stretching and bending bands of water molecules along with the CO and SO3 stretching bands of the surfactant molecules, showed that water was selectively and almost completely extracted from the aqueous core of the reversed micelles. Changes in the surroundings of the nanoparticles surface were monitored by photoluminescence spectroscopy and variations in the emission band profiles indicated enhanced luminescence properties. The latter finding, as well as the inhibition of the nanoparticles growth process, are attributable to the progressive reduction of water content in the core of the reversed micelles.

Keywords: Nanoparticles; Microemulsion; Microwave irradiation; CdS; Photoluminescence

Solvent effect on CO oxidation as a novel diagnosing tool to pin down low-coverage CO at the liquid–solid interface: An in situ infrared study by Zhen Ma (pp. 419-430).
In situ probing of liquid–solid interfaces is important for understanding heterogeneous liquid-phase catalysis and other interfacial phenomena, but the spectroscopic interference from the bulk is often a problem. Some organics may have infrared features overlapping the adsorbed CO peaks, making the determination of adsorbed CO difficult. In this study, CCl4-flushing was used as a novel diagnosing tool to pin down the low-coverage CO derived from decarbonylation of organics. This diagnosing tool was designed based on our in situ reflection–absorption infrared spectroscopy results reported here that there is a marked solvent effect (water>ethanol>methanol>cyclohexane>benzene∼carbon tetrachloride) on CO oxidation at the liquid–solid interface. Possible reasons for that solvent effect were discussed.Solvent effect (water>ethanol>methanol>cyclohexane>benzene∼carbon tetrachloride) on CO oxidation at the liquid–solid interface was identified by FT-IR. This solvent effect was then employed to design a novel diagnosing tool to pin down the low-coverage CO derived from decarbonylation of organics.

Keywords: Liquid–solid interface; Reflection–absorption infrared spectroscopy; CO oxidation; Solvent effect; α; -Ketoester; Decarbonylation

Metal-cation-mediated nanocrystal arrays of sandwich-type (phthalocyaninato) [tetrakis(4-pyridyl)porphyrinato] cerium complex formed at the water–chloroform interface by Qingyun Liu; Yongzhong Bian; Hongguo Liu; Xueying Wang; Yanli Chen; Xiyou Li; Jianzhuang Jiang (pp. 431-436).
Regular square, wirelike, quadrate, and rodlike nanocrystal arrays of Cd2+, Hg2+, or Ag+ metal-cation-mediated sandwich-type mixed (phthalocyaninato) [5,10,15,20-tetrakis(4-pyridyl)poprhyrinato] cerium(III) double-decker complex Ce(Pc)(TPyP) have been successfully prepared at the water–chloroform interface. The nanocrystal growth processes were monitored by transmission electron microscopy (TEM), which reveals that different morphologies of nanocrystals have been fabricated from double-decker molecules connected by different kinds of metal cations, forming coordination polymers. These nanoscaled coordination polymers were characterized by FT-IR spectra and energy-dispersive X-ray spectra (EDS). EDS results clearly revealed the elements of the nanocrystals and the FT-IR spectra give evidence for the coordination interaction between the double-decker molecules and metal cations. The UV–vis absorption spectrum indicates the formation of J-aggregates of the double-decker molecules in the nanocrystals formed.Different morphologies of nanocrystals have been fabricated from double-decker molecules connected by different kinds of metal cations as connectors, forming coordination polymers.

Keywords: Phthalocyanine; Porphyrin; Cerium; Sandwich complex; Transmission electron microscopy; Nanocrystal

Fabrication of hollow multifunctional spheres containing MCM-41 nanoparticles and magnetite nanoparticles using layer-by-layer method by Sajanikumari Sadasivan; Gleb B. Sukhorukov (pp. 437-441).
Macroscopic mesoporous silica spheres have been fabricated by alternatively depositing preformed MCM-41 nanoparticles and polyelectrolytes onto polystyrene lattices. High surface area hollow mesoporous spheres were obtained by removal of the core by solvent or calcination. Further, the versatility of the layer-by-layer (LBL) method was extended to fabricate magnetite-mesoporous silica composites by depositing magnetite and MCM-41 nanoparticles onto polystyrene beads. Such high surface area composites are important since the mesopores can be used for encapsulation of varied materials like enzymes and drugs while the presence of magnetite ensures application in biocatalysis and separation under magnetic field.Mesoporous silica–magnetite hollow shells have been fabricated by depositing MCM-41 nanoparticles (100 nm) and magnetite nanoparticles (10 nm) along with polyelectrolytes onto polystyrene beads using the facile layer-by-layer method.

Keywords: Mesoporous; Layer-by-layer; Magnetite; MCM-41; Polyelectrolytes; Capsules

A level set method for determining critical curvatures for drainage and imbibition by Maša Prodanović; Steven L. Bryant (pp. 442-458).
An accurate description of the mechanics of pore level displacement of immiscible fluids could significantly improve the predictions from pore network models of capillary pressure–saturation curves, interfacial areas and relative permeability in real porous media. If we assume quasi-static displacement, at constant pressure and surface tension, pore scale interfaces are modeled as constant mean curvature surfaces, which are not easy to calculate. Moreover, the extremely irregular geometry of natural porous media makes it difficult to evaluate surface curvature values and corresponding geometric configurations of two fluids. Finally, accounting for the topological changes of the interface, such as splitting or merging, is nontrivial. We apply the level set method for tracking and propagating interfaces in order to robustly handle topological changes and to obtain geometrically correct interfaces. We describe a simple but robust model for determining critical curvatures for throat drainage and pore imbibition. The model is set up for quasi-static displacements but it nevertheless captures both reversible and irreversible behavior (Haines jump, pore body imbibition). The pore scale grain boundary conditions are extracted from model porous media and from imaged geometries in real rocks. The method gives quantitative agreement with measurements and with other theories and computational approaches.The progressive quasi-static algorithm identifies critical curvatures in throat drainage and pore imbibition. The method is robust with respect to porous sample geometry and automatically handles the merger and splitting of multiple menisci.

Keywords: Level set method; Immiscible fluid displacement; Porous media; Drainage; Imbibition

Influence of 4-cyano-4′-biphenylcarboxylic acid on the orientational ordering of cyanobiphenyl liquid crystals at chemically functionalized surfaces by Joon-Seo Park; Chang-Hyun Jang; Matthew L. Tingey; Aaron M. Lowe; Nicholas L. Abbott (pp. 459-473).
We report two methods that involve tailoring of the chemical composition of the nematic liquid crystal 4-cyano-4′-pentylbiphenyl to achieve control over the orientational ordering of the liquid crystal on chemically functionalized surfaces. The first method involves the direct addition of 4-cyano-4′-biphenylcarboxylic acid to 4-cyano-4′-pentylbiphenyl. The second method involves exposure of 4-cyano-4′-pentylbiphenyl to ultraviolet light and photochemical generation of a range of products, including 4-cyano-4′-biphenylcarboxylic acid. The addition of the acid or exposure to ultraviolet light accelerated the rate at which the liquid crystal exhibited an orientational transition from planar to perpendicular (homeotropic) alignment on surfaces presenting ammonium groups. The appearance of the homeotropic orientation of the UV-treated 4-cyano-4′-pentylbiphenyl on ammonium-terminated surfaces was dependent on the thickness of the film of liquid crystal (13–50 μm), consistent with a dipolar coupling between the liquid crystal and the electric field associated with an electrical double layer generated at the ammonium surface. Although the addition of 4-cyano-4′-biphenylcarboxylic acid or UV treatment of the liquid crystal also promoted homeotropic orientations on surfaces presenting hydroxyl groups, the orientations of the UV-treated liquid crystal on the hydroxyl-terminated surface did not change with thickness of the film of liquid crystal in the manner observed on the ammonium-terminated surfaces. The latter result indicates that the mechanism leading to homeotropic anchoring on hydroxyl-terminated surfaces is distinct from that on ammonium-terminated surfaces. Measurements performed using polarization modulation infrared reflection–absorption spectroscopy suggest that hydrogen bonding between the 4-cyano-4′-biphenylcarboxylic acid and the hydroxyl-terminated surface is responsible for the homeotropic anchoring on the surface. Finally, the orientation of the liquid crystal on methyl-terminated surfaces was not influenced by the addition of 4-cyano-4′-biphenylcarboxylic acid nor UV treatment. These results illustrate how the chemical composition of liquid crystals can be manipulated to achieve control over their ordering on surfaces that possess chemical functionality relevant to the development of liquid crystal-based sensors and diagnostic tools. We illustrate the utility of this approach by using the tailored liquid crystal to amplify and optically transduce the presence of proteins arrayed on ammonium-terminated surfaces.We introduce two methods that permit manipulation of the anchoring of the nematic liquid crystal 4-cyano-4′-pentylbiphenyl (5CB) on various chemically functionalized organic surfaces.

Keywords: Liquid crystal; Chemically functionalized surface; Electrical double layers; Hydrogen bonding; Orientational ordering; Anchoring; Acid dopant; UV treatment

Surfactants with an amide group “spacer?: Synthesis of 3-(acylaminopropyl)trimethylammonium chlorides and their aggregation in aqueous solutions by Paulo A.R. Pires; Omar A. El Seoud (pp. 474-485).
The cationic surfactants RCONH(CH2)3N+(CH3)3Cl, where RCO = C10, C12, C14, and C16, respectively, have been synthesized by reacting the appropriate carboxylic acids with 3-N,N-dimethylamino-1-propylamine, followed by dehydration of the ammonium salt produced. Reaction of the intermediates obtained (RCONH(CH2)3N(CH3)2) with methyl iodide, followed by chloride/iodide ion-exchange furnished the surfactants. Their adsorption and aggregation in aqueous solutions have been studied by surface tension, conductivity, EMF, static light scattering and FTIR. Additional information on the micellar structure was secured from effects of the medium on the1H NMR chemical shifts and 2D ROESY spectra. Increasing the length of the acyl moiety increased the micelle aggregation number, and decreased the minimum area/surfactant molecule at the solution/air interface, the critical micelle concentration, and the degree of dissociation of the counter-ion. Gibbs free energies of adsorption at the solution/air interface and of micelle formation were calculated, and compared to those of 2-(acylaminoethyl)trimethylammonium chloride; alkyl trimethylammonium chloride; and benzyl(3-acylaminopropyl)dimethylammonium chloride surfactants. For both processes (adsorption and micellization), contributions of the CH2 groups in the hydrophobic tail and of the head-group toΔG0 were calculated. The former contribution was found to be similar to those of other cationic surfactants, whereas the latter one is more negative than those of 2-(acylaminoethyl)trimethylammonium chlorides and trimethylammonium chlorides. This is attributed to a combination of increased hydrophobicity of the head-group, and (direct- or water-mediated) intermolecular hydrogen-bonding of aggregated monomers, via the amide group. FTIR and NMR results indicated that the amide group lies at the micellar interface.

Keywords: Cationic micelles; Synthesis of; Cationic surfactants; Micellar properties of; Surfactants with a spacer; Surface tension; Conductance; FTIR; NMR; ISE; Amide head-group

Cloud point extraction and graphite furnace atomic absorption spectrometry determination of manganese(II) and iron(III) in water samples by Pei Liang; Hongbo Sang; Zhimei Sun (pp. 486-490).
Cloud point extraction (CPE) was applied as a preconcentration step prior to graphite furnace atomic absorption spectrometry (GFAAS) determination of manganese(II) and iron(III) in water samples. After complexation with 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone (PMBP), the analytes could be quantitatively extracted to the phase rich in the surfactant p-octylpolyethyleneglycolphenylether (Triton X-100) and be concentrated, then determined by GFAAS. The parameters affecting the extraction efficiency, such as solution pH, concentration of PMBP and Triton X-100, equilibration temperature and time, were investigated in detail. Under the optimum conditions, preconcentration of 10 ml of sample solution permitted the detection of 0.02 ng ml−1 of Mn(II) and 0.08 ng ml−1 of Fe(III) with enrichment factors of 31 and 25 for Mn(II) and Fe(III), respectively. The proposed method was applied to determination of trace manganese(II) and iron(III) in water samples with satisfactory results.After complexation with 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone (PMBP), Mn(II) and Fe(III) could be quantitatively extracted to the phase rich in the surfactant Triton X-100 and be concentrated, then determined by graphite furnace atomic absorption spectrometry.

Keywords: Cloud point extraction; Graphite furnace atomic absorption spectrometry; Manganese(II); Iron(III)

Conductometric and fluorometric investigations on the mixed micellar systems of cationic surfactants in aqueous media by Sarah E. Moore; Michael Mohareb; Stephanie A. Moore; Rama M. Palepu (pp. 491-496).
Micellar properties of binary mixtures of hexadecyldiethylethanolammonium bromide surfactant with tetradecyldimethylammonium, trimethylammonium, triphenylphosphonium, diethylethanolammonium, and pyridinium bromide surfactants have been characterized employing conductometric and fluorescence techniques. The critical micelle concentration (cmc) and the degree of counter-ion binding values ( δ) of the binary systems were determined from the conductivity measurements. The results were analyzed in light of various existing theories to calculate micellar composition, activity coefficients, and the interaction parameter ( β). Partial contribution of each surfactant, cmc1, cmc2, to the overall cmc value was also evaluated. Aggregation numbers and micropolarity of the mixed micelles were determined from fluorescence measurements. The results were discussed in terms of synergetic interactions in these systems on the basis of the head group/head group and tail/tail interactions and the counter-ion binding.

Keywords: Cationic surfactants; Conductivity; Mixed micelles; Interaction parameters; Activity coefficients

Influence of polyethylene oxide on the rheological properties of semidilute, wormlike micellar solutions of hexadecyltrimethylammonium chloride and sodium salicylate by Siriluck Suksamranchit; Anuvat Sirivat; Alexander M. Jamieson (pp. 497-504).
The influence of polyethylene oxide (PEO) on the rheological properties of equimolar wormlike micellar solutions of hexadecyltrimethylammonium chloride (HTAC) and sodium salicylate (NaSal) is investigated, above the concentration where a micellar entanglement network is formed. PEO is known to have a temperature-dependent binding affinity for HTAC micelles. The influence of temperature, PEO concentration, and HTAC concentration is explored. Within the concentration and temperature range examined (25–100 mM HTAC and 25–50 °C), HTAC/NaSal solutions exhibit rheological characteristics of an entanglement network. Application of transient network theory provides information in the form of the plateau modulus,G∞′, the terminal viscoelastic relaxation time,τR, the reptation time,τrep, the micellar breaking time,τbr, the mean micellar length,L¯, and the entanglement length,le. Consistent with literature data, increase of HTAC concentration results in an evolution from slow-breaking to fast-breaking behavior, accompanied by an increase inG∞′ andτrep, and decreases inτR, andτbr,le andL¯. Addition of PEO results in a substantial decrease inG∞′ (increase inle), and corresponding increases inτR andL¯. These observations are consistent with the idea that binding of HTAC micelles to PEO in aqueous solution decreases the number of surfactant molecules available to contribute to the entanglement network of wormlike micelles.

Keywords: Surfactant wormlike micelle; Polyethylene oxide; Rheology

Estimation of the zeta potential and the dielectric constant using velocity measurements in the electroosmotic flows by H.M. Park; S.M. Hong (pp. 505-511).
In this paper we develop a method for the determination of the zeta potential ζ and the dielectric constant ε by exploiting velocity measurements of the electroosmotic flow in microchannels. The inverse problem is solved through the minimization of a performance function utilizing the conjugate gradient method. The present method is found to estimate ζ and ε with reasonable accuracy even with noisy velocity measurements.Estimation of the zeta potential and the dielectric constant has been performed using velocity measurements in the electroosomotic flows. (a) Measurement location in a three-dimensional straight microchannel. Contours of axial velocity are also plotted. (b) Estimation error of ζ versus frequency of the external potential ω. (c) Estimation error of ε versus ω.

Keywords: Electroosmotic flow; Estimation of zeta potential and dielectric constant; Inverse problem

Conductometric evidence for intact polyion-induced liposome clusters by F. Bordi; C. Cametti; S. Sennato; D. Viscomi (pp. 512-517).
In this note, we present a set of electrical conductivity measurements of polyion-induced liposome aggregate aqueous suspensions that supports evidence for the existence of a cluster phase in low-density colloidal systems. Heavily NaCl-loaded liposomes, dispersed in a low-conductivity aqueous solution, are forced by electrostatic interactions with oppositely charged polyions to build up into individual aggregates, where the single vesicles maintain their integrity and, upon an external force, are able to release their ionic content. The conductivity data, within the effective medium approximation theory for heterogeneous systems, are in agreement with the picture of a suspension built up by clusters of vesicles which are able to preserve their content from the external medium. This finding opens new possibilities in multicompartment drug delivery techniques.The release of ion content: (c) Polyion-induced NaCl-loaded liposome aggregates. (d) Liposomes release their ionic content.

Keywords: Liposome; Polyion-induced aggregation; Electrical conductivity; Liposome cluster

Experimental humidity dependency of small particle adhesion on silica and titania by Matti Paajanen; Jukka Katainen; Olli H. Pakarinen; Adam S. Foster; Jouko Lahtinen (pp. 518-523).
The humidity present in ambient atmosphere affects the adhesion of small particles by causing capillary bridge formation between the particle and the surface. Even in moderate relative humidities this, usually attractive, force can have a significant effect on adhesion behaviour of micro and sub-micro particles. We have directly measured the pull-off forces of initially adhered oxide particles on oxide surfaces with atomic force microscope in controlled atmosphere with adjustable humidity. We demonstrate the effect of the surface roughness resulting in two different regions of capillary formation and the particle shape having a strong effect on the humidity dependency of adhesion. The experimental results are explained by theoretical framework.Measured humidity dependent adhesion of (a) silica probe and (b) titania probe on silica surface showing two regions of advancing meniscus formation.

Keywords: Capillary; AFM; Adhesion; Humidity

Adhesion as an interplay between particle size and surface roughness by J. Katainen; M. Paajanen; E. Ahtola; V. Pore; J. Lahtinen (pp. 524-529).
Surface roughness plays an important role in the adhesion of small particles. In this paper we have investigated adhesion as a geometrical effect taking into account both the particle size and the size of the surface features. Adhesion is studied using blunt model particles on surfaces up to 10 nm root-mean-square (RMS) roughness. Measurements with particles both smaller and larger than surface features are presented. Results indicate different behavior in these areas. Adhesion of particles smaller than or similar in size to the asperities depend mainly on the size and shape of the asperities and only weakly on the size of the particle. For large particles also the particle size has a significant effect on the adhesion. A new model, which takes the relative size of particles and asperities into account, is also derived and compared to the experimental data. The proposed model predicts adhesion well over a wide range of particle/asperity length scales.Adhesion of particles smaller than the asperities depends mainly on the size and shape of the asperities. For large particles, also particle size has significant effect.

Keywords: Adhesion; Surface roughness; Pull-off force; Atomic force microscope

Self-generation of concentration gradients of divalent cations in commercial bentonite membrane during ultrafiltration by S. Chatterji (pp. 530-534).
Research workers, working with commercial bentonite-based membranes, reported different diffusivity for co- and counterions through those membranes. Many of these researchers called this difference in diffusivity ultrafiltration. Some of these workers also noted that commercial bentonite membranes often contain divalent metal carbonates as impurities. Recently it has been suggested that the ultrafiltration is associated with the co-diffusion of divalent metal ions. Previous workers did not recognize this co-diffusion, probably due to an absence of imposed concentration gradient for the divalent metal ions. The present investigation suggests that the required concentration gradient is self-generated by increased solubility of the divalent metal carbonates with increasing concentration of alkali halide in solution. The presence of dissolved divalent metal ions alters the interfacial potentials at the outside solution and bentonite membrane junctions and reduces the electrostatic potential gradient across the membrane. A reduction in the electrostatic potential gradient across the membrane reduces the coupling between the diffusing co- and counterions and alters their diffusivity.Through clay membranes cation and anion migrate at different rates (see the figure). This known as ultrafiltration. The origin of this ultrafiltration has been traced to increasing solubility of divalent carbonates eith increasing alkali halide concentration in the diffusant.

Keywords: Bentonite; Membrane; Ultrafiltration; Divalent cation; Diffusion; Electrostatic potential; Self-generation of concentration gradient

Experimental investigation of nanoparticle dispersion by beads milling with centrifugal bead separation by Mitsugi Inkyo; Takashi Tahara; Toru Iwaki; Ferry Iskandar; Christopher J. Hogan Jr.; Kikuo Okuyama (pp. 535-540).
A new type of beads mill for dispersing nanoparticles into liquids has been developed. The bead mill utilizes centrifugation to separate beads from nanoparticle suspensions and allows for the use of small sized beads (i.e. 15–30 μm in diameter). The performance of the beads mill in dispersing a suspension of titanium dioxide nanoparticle with 15 nm primary particles was evaluated experimentally. Dynamic light scattering was used to measure titania particle size distributions over time during the milling process, and bead sizes in the 15–100 μm range were used. It was found that larger beads (50–100 μm) were not capable of fully dispersing nanoparticles, and particles reagglomerated after long milling times. Smaller beads (15–30 μm) were capable of dispersing nanoparticles, and a sharp peak around 15 nm in the titania size distribution was visible when smaller beads were used. Because nanoparticle collisions with smaller beads have lower impact energy, it was found by X-ray diffraction and transmission electron microscopy that changes in nanoparticle crystallinity and morphology are minimized when smaller beads are used. Furthermore, inductively-coupled plasma spectroscopy was used to determine the level of bead contamination in the nanoparticle suspension during milling, and it was found that smaller beads are less likely to fragment and contaminate nanoparticle suspensions. The new type of beads mill is capable of effectively dispersing nanoparticle suspensions and will be extremely useful in future nanoparticle research.

Keywords: Nanoparticles; Dispersing machine; Dispersing process; Agglomeration; Beads mill; Media mill; Colloidal particles; Titania nanoparticles

Ions at the air/water interface by Marian Manciu; Eli Ruckenstein (pp. 541-544).
In a recent review of this topic [B.C. Garett, Science 303 (2004) 1146] the emphasis was on some recent experiments, in which it was found that some anions accumulate at the air/water interface and not in the bulk, as usually happens to the cations, and on some simulations which explained those positive surface adsorption excesses. Because a large number of these experiments could be explained on the basis of some simple physical models proposed by the authors for the interaction between the ions and the air/water interface [M. Manciu, E. Ruckenstein, Adv. Colloid Interface Sci. 105 (2003) 63; Adv. Colloid Interface Sci. 112 (2004) 109; Langmuir 21 (2005) 11312], those models are reviewed in the present note, the goal being to draw attention to them.Humic acid acts a polyvalent anion neutralizing the positive charges on CTAB micelles in a manner similar to the reaction between charged polymers and surfactants. At high CTAB concentration the hexagonal array structure of CTAB micelles was preserved, though deformed by the interaction, suggesting that there is no regular repetition of structural units in humic acid because such structural regularity would have caused the formation of new CTAB structures.

Keywords: Interface; Ions; Double layer; Ion-hydration forces

TiO2 anatase-based membranes with hierarchical porosity and photocatalytic properties by Florence Bosc; Patrick Lacroix-Desmazes; André Ayral (pp. 545-548).
Taking benefit of previously obtained results, stable complex organic–inorganic hybrid suspensions are successfully prepared by mixing a polystyrene latex aqueous suspension, a titania hydrosol and a nonionic triblock copolymer. These suspensions can be then deposited as thin films on dense or porous substrates. Solvent evaporation induces the formation of spherical micelles by self-assembly of the amphiphilic molecules during the drying of the films. Two types of isolated spherical macropores (few ten nanometers) and mesopores (4–5 nm) are generated inside the layers by the thermal removal of the polystyrene particles and of the micelles, respectively. The remaining inorganic network exhibits an additional interconnected microporosity with a mean pore size of 1.5 nm, resulting from the aggregation of the anatase nanoparticles. A complete removal of the templating units at low temperature is possible using the photocatalytic properties of the anatase network. Such layers exhibit attractive properties for the design of ceramic membranes. They can be advantageously used in order to increase the permeability of the separative layer and to reduce the number of intermediate layers of these asymmetric structures.Hierarchical anatase-based membrane consisting in isolated spherical macropores (a), isolated mesopores (b), and nanocrystalline anatase walls with interconnected micropores (c).

Keywords: Hierarchical porosity; Membrane; Anatase; Photocatalytic activity

Correlation between surface tension and critical temperatures of liquid metals by Sidney Blairs; Mohammad Hassan Abbasi (pp. 549-553).
The inter-relationship of surface tension σ, molar volume V, and critical temperatureTc has been examined using experimental values for eighteen liquid metals. Hard-sphere diameters a correlate with the equationa5/2=8.9733×10−19V(σ/Tc)1/4−1.0459×10−25. UnknownTc may be estimated using surface tension and liquid density values.Hard-sphere diameters of liquid metals a are correlated with molar volume V, surface tension σ, and critical temperatureTc.

Keywords: Liquid metals; Critical temperatures; Surface tension; Density

Extracellular polymeric bacterial coverages as minimal area surfaces by Alberto Saa; Omar Teschke (pp. 554-557).
Surfaces formed by extracellular polymeric substances enclosing individual and some small communities of Acidithiobacillus ferrooxidans on plates of hydrophobic silicon and hydrophilic mica are analyzed by means of atomic force microscopy imaging. Accurate nanoscale descriptions of such coverage surfaces are obtained. The good agreement with the predictions of a rather simple but realistic theoretical model allows us to conclude that they correspond, indeed, to minimal area (constant mean curvature) surfaces enclosing a given volume associated with the encased bacteria. This is, to the best of our knowledge, the first shape characterization of the coverage formed by these biomolecules, with potential applications to the study of biofilms.AFM imaging is used to show that the EPS coverages enclosing individual and some small communities of Acidithiobacillus ferrooxidans correspond to minimal area surfaces.

Keywords: Extracellular polymeric substances; Bacterial coverage; Surface tension; Minimal area surfaces

Solubility measurement of methane in aqueous solution of sodium dodecyl sulfate at ambient temperature and near hydrate conditions by Bao-Zi Peng; Guang-Jin Chen; Hu Luo; Chang-Yu Sun (pp. 558-561).
Solubility data of methane in aqueous solutions of sodium dodecyl sulfate (SDS) with different concentrations were measured at ambient temperature and near hydrate conditions. The critical micelle concentration (CMC) and the number of methane molecules dissolved in each micelle of the methane + water + SDS system were calculated and compared with those of the ethylene + water + SDS system. The results demonstrated that the micelles could be formed in the SDS concentration range where an efficient promotion effect on hydrate formation was previously reported; the micelle solubilization to methane molecules was remarkable near hydrate conditions, and the ethylene molecules could be solubilized in micelles in preference to methane molecules.Methane solubility varies with SDS concentration andP/T conditions. SDS can form micelles at concentrations of efficient promotion to hydrate formation and micelle solubilization was remarkable near hydrate conditions.

Keywords: Solubility; Methane; Sodium dodecyl sulfate; Critical micelle concentration; Hydrate

Filtration of deformable emulsion droplets by T.F. Headen; S.M. Clarke; A. Perdigon; G.H. Meeten; J.D. Sherwood; M. Aston (pp. 562-565).
Oil-in-water (o/w) emulsions of different droplet size were filtered on membranes of various pore sizes to investigate the growth and behaviour of o/w filter cakes. The cake desorptivity S and the filter membrane resistance R were measured at various filtration pressures P. The variation of S with P shows that filter cake oil droplets of radius a are effectively rigid forP≪γ/a and fully deformable forP≫γ/a, where γ is the oil–water interfacial tension. For the largest P, when S became P-independent, the filter cake remained water-permeable as expected from theory.Although relatively rigid when the driving pressures are small, emulsion droplets are found to increasingly deform under larger applied pressures. Interestingly, the gaps between the droplets never completely close even at the highest pressures.

Keywords: Emulsion; Emulsion fractionation; Soft solids; Monodisperse; Ion-track etched membranes; Filtration; Desorptivity; Permeability; Deformation; Push through

No Title by Arthur Hubbard (pp. 566-566).
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