Journal of Colloid And Interface Science (v.288, #1)

Preparation and self-assembly of uniform TiO2/SiO2 composite submicrospheres by Lixia Liu; Peng Dong; Renxiao Liu; Qian Zhou; Xiaodong Wang; Guiyun Yi; Bingying Cheng (1-5).
Monodisperse spheres of silica were uniformly coated with titania through the hydrolysis of titanium alkoxide in order to increase the refractive index of complex submicrospheres and keep their monodispersity as well as their surface morphology. On the basis of the hydrolysis of tetrabutyl orthotitanate (TBOT), a continuous-feeding procedure was used to fabricate 10-nm titania coatings on monodisperse colloidal silica submicrospheres of diameter 200 nm. The TiO2/SiO2 composite spheres were assembled to achieve structures with three-dimensional order by gravity sedimentation and vertical deposition. The complex sphere composition, quality, and morphology were characterized by different techniques.
Keywords: TBOT; TiO2/SiO2 composite submicrospheres; Self-assembly; Colloidal crystals; Photonic bandgap;

Microcalorimetry of the adsorption of lysozyme onto polymeric substrates by Valerie A. Lee; Robert G. Craig; Frank E. Filisko; Robert Zand (6-13).
The conformation of blood proteins adsorbed on biomaterial surfaces probably plays a significant role in the biocompatibility of blood-contacting implants. This paper reports heats of adsorption of a globular protein, lysozyme, onto three uncharged polymeric substrates. Variations in heats among substrates reflect differences in the lysozyme/substrate interaction as well as the possibility of substrate-dependent conformations. In each case, a series of plateaus appeared in the adsorption isotherm with increasing concentration. In the cases of two substrates, polystyrene and poly(styrene-co-butyl methacrylate), endothermic discontinuities appeared at rises between plateaus. It is proposed that the step pattern in each isotherm reflects distinct conformational states of lysozyme on the substrate surfaces. Endothermic discontinuities may be latent heats associated with change to a more stable conformation after initial adsorption. The absence of discontinuities in the case of poly(styrene-co-allyl alcohol) suggests structural transitions occur to a smaller extent on this material and results in conformations different from those which occur when lysozyme is adsorbed by polystyrene or by poly(styrene-co-butyl methacrylate).
Keywords: Lysozyme; Protein adsorption; Protein conformation; Microcalorimetry; Biocompatibility; Interfacial energy;

Th(IV) adsorption on alumina: Effects of contact time, pH, ionic strength and phosphate by Zhi-Jun Guo; Xing-Min Yu; Fei-Hu Guo; Zu-Yi Tao (14-20).
Adsorption of Th(IV) (total concentration, 10 −5 – 10 −4   mol / L ) was studied by a batch technique. The effects of pH, ionic strength, contact time, and phosphate on the adsorption of Th(IV) onto alumina were investigated. Adsorption isotherms of Th(IV) on alumina at approximately constant pH and three ionic strengths (0.05, 0.1, 0.5 mol/L KNO3) were determined. It was found that the pH values of aqueous solutions of both the Th(IV)–alumina and phosphate–alumina adsorption systems increase with increasing contact time, respectively. Adsorption of Th(IV) on alumina steeply increases with increasing pH from 1 to 4.5 and the adsorption edge consists of three regions. The phosphate added clearly enhances Th(IV) adsorption in the pH range 1–4. From the adsorption isotherms at approximately constant pH and three different ionic strengths, a reduced ionic strength effect was observed and is contradictory to the insensitive effect obtained from the adsorption edges on three oxides of Fe, Al, and Si at different ionic strengths. Compared with the adsorption edges at different ionic strengths, the adsorption isotherms at approximately constant pH and different ionic strengths are more advantageous in the investigation of ionic strength effect. The significantly positive effect of phosphate on Th(IV) adsorption onto alumina was attributed to strong surface binding of phosphate on alumina and the subsequent formation of ternary surface complexes involving Th(IV) and phosphate.
Keywords: Th(IV); Alumina; Adsorption; pH; Phosphate;

Adsorption and desorption of copper and zinc in the surface layer of acid soils by M. Arias; C. Pérez-Novo; F. Osorio; E. López; B. Soto (21-29).
The environmental and health effects of the contamination of soils by heavy metals depend on the ability of the soils to immobilize these contaminants. In this work, the adsorption and desorption of Cu and Zn in the surface layers of 27 acid soils were studied. Adsorption of CuII from 157–3148 μmol L−1 solutions was much greater than adsorption of ZnII from solutions at the same concentration. For both Cu and Zn, the adsorption data were fitted better by the Freundlich equation than by the Langmuir equation. Multiple regression analyses suggest that Cu and Zn adsorption depends to a significant extent on pH and CEC: for both metals these variables accounted for more than 80% of the variance in the Freundlich pre-exponential parameter K F , and pH also accounted for 57% of the variance in 1 / n for Zn and, together with carbon content, for 41% of the variance in 1 / n for Cu. The percentage of adsorbed metal susceptible to desorption into 0.01 M NaNO3 was greater for Zn than for Cu, but in both cases depended significantly on pH, decreasing as pH increased. In turn, both pHH2O and pHKCl are significantly correlated with cation exchange capacity. Desorption of metal adsorbed from solutions at relatively low concentration (787 μmol L−1) exhibited power-law dependence on K d , the quotient expressing distribution between soil and soil solution in the corresponding adsorption experiment, decreasing as increasing K d reflected increasing affinity of the soil for the metal. The absence of a similarly clear relationship when metal had been adsorbed from solutions at relatively high concentration (2361 μmol L−1) is attributed to the scant between-soil variability of K d at these higher concentrations. In general, adsorption was greater and subsequent desorption less in cultivated soils than in woodland soils.
Keywords: Adsorption–desorption; Copper; Zinc; Acid soils;

Adsorption of a model anionic dye, eosin Y, from aqueous solution by chitosan hydrobeads by Sudipta Chatterjee; Sandipan Chatterjee; Bishnu P. Chatterjee; Akhil R. Das; Arun K. Guha (30-35).
The process of sorption is being increasingly used for ecofriendly and economic remediation of textile dye effluents. The present model study deals with the adsorption of a model anionic dye, eosin Y, from wastewater using conditioned chitosan hydrobeads. Conditioning reduced the pH sensitivity and maintained the maximum sorption capacity of the beads near pH 8. To understand the chemicophysical characteristics of the adsorption process we studied, the kinetics and isotherm behavior of the system. It was observed that temperature played a significant role in the process. The Langmuir model was found to be most appropriate for the description of the adsorption process. The kinetic results followed a second-order equation. It was observed that 1 g of chitosan adsorbed ∼ 76   mg of eosin Y. The dye was desorbed from the beads by changing the pH of the solution, and the conditioned chitosan beads were reused five times without any loss of mechanical and chemical efficacy.
Keywords: Bioremediation; Anionic dye; Chitosan hydrobeads; Chemicophysical study;

Classical theoretical assumptions, which are implausible for describing biological behavior in real systems include uniform fixed charge distribution in colloidal outer membrane layer, uniform dielectric constant throughout the membrane phase, and point charge for ionic sizes. In the present study, absorption of cations by fixed functional groups in the membrane layer, variation in dielectric constant in a system, and effect of ionic sizes are considered to investigate the deposition of biocolloids each covered with an ion-penetrable membrane. The simulated results reveal that a larger numbers of cations involved in the formation of a cations–fixed groups complex, a smaller dielectric constant near a biological uncharged core, a larger dielectric constant of the membrane phase, a smaller cation-absorption equilibrium constant, a smaller concentration of total functional groups in the membrane layer, a thicker membrane, smaller cations, larger anions, and larger functional groups yield a faster rate of deposition.
Keywords: Cation absorption; Dielectric constant; Size; Deposition; Rate; Biocolloid;

Synthesis of zirconocene-based silica phases and evaluation in lindane and heptachlor epoxide adsorption/desorption by Ana Maria Geller; Fernanda Chiarello Stedile; Maria do Carmo Ruaro Peralba; Tânia Mara Pizzolato; João Henrique Zimnoch dos Santos (45-54).
Silica (350 m2 g−1) was chemically modified with Cp2ZrCl2 and (nBuCp)2ZrCl2 by grafting. Hybrid silica bearing surface indene groups was synthesized by the sol–gel method, followed by metallation with ZrCl4⋅2THF. The resulting phases were characterized by Rutherford backscattering spectrometry (RBS), 13C and 29Si magic angle spin nuclear magnetic resonance, X-ray photoelectron spectroscopy, and diffuse reflectance infrared Fourier transform spectroscopy. According to RBS measurements, metal content was 0.2- to 0.3-wt% Zr/SiO2 for the grafted systems and 4.5-wt% Zr/SiO2 for the phase prepared by the sol–gel method. The solid phases were evaluated for the adsorption/preconcentration of lindane and heptachlor epoxide from aqueous solution. For comparative reasons, the commercial LC-18 phase was also evaluated. Analyte concentration was monitored by gas chromatography electron capture detection. For the grafted phases, the coordination sphere around the metal center seems not to influence the adsorption/desorption properties of these phases vis-à-vis the studied analytes. In the case of the phases prepared by the sol–gel method, recovery results were comparable to those observed for LC-18. Experiments using ZrO2 and ZrO2/SiO2 phases led to lower recovery results.
Keywords: Organochlorine compounds; Solid-phase extraction; Pesticides; Extraction methods; Silica;

Adsorption of As(III) from aqueous solutions by iron oxide-coated sand by V.K. Gupta; V.K. Saini; Neeraj Jain (55-60).
Arsenic is a toxic element and may be found in natural waters as well as in industrial waters. Leaching of arsenic from industrial wastewater into groundwater may cause significant contamination, which requires proper treatment before its use as drinking water. The present study describes removal of arsenic(III) on iron oxide-coated sand in batch studies conducted as a function of pH, time, initial arsenic concentration, and adsorbent dosage. The results were compared with those for uncoated sand. The adsorption data fitted well in the Langmuir model at different initial concentration of As(III) at 20 g/l fixed adsorbent dose. Maximum adsorption of As(III) for coated sand is found to be much higher (28.57 μg/g) than that for uncoated sand (5.63 μg/g) at pH 7.5 in 2 h. The maximum As(III) removal efficiency achieved is 99% for coated sand at an adsorbent dose of 20 g/l with initial As(III) concentration of 100 μg/l in batch studies. Column studies have also been carried out with 400 μg/l arsenic (pH 7.5) by varying the contact time, filtration rate, and bed depth. Results of column studies demonstrated that at a filtration rate of 4 ml/min the maximum removal of As(III) observed was 94% for coated sand in a contact time of 2 h. The results observed in batch and column studies indicate that iron oxide-coated sand is a suitable adsorbent for reducing As(III) concentration to the limit (50 μg/l) recommended by Indian Standards for Drinking Water.
Keywords: Iron oxide; Coated sand; Adsorbent; Adsorption; Arsenic; Flow rate;

Micrometer-sized polystyrene/poly(n-butyl methacrylate) composite particles of hemisphere morphology and narrow size distribution were prepared by a process of single-step swelling of uniform polystyrene template microspheres with emulsion droplets of the monomer n-butyl methacrylate containing the initiator benzoyl peroxide in the presence, or absence, of the co-swelling agent toluene. Butyl methacrylate was then polymerized at 73 °C within the template microspheres. Surface and bulk characterization of the particles were performed by methods such as FTIR, elemental analysis, XPS, advancing contact angle, light microscope, SEM, and cross-sectional TEM. Selective surface functionalization of the poly(n-butyl methacrylate) phase of the composite particles was performed by carrying out a similar swelling and polymerization process in the presence of a water-soluble vinylic monomer such as acrylamide.
Keywords: Microspheres; Poly(n-butyl methacrylate); Template; Composite; Hemisphere; Single-step swelling;

Electrorheological behavior of suspensions of a substituted polyaniline with long alkyl pendants by Dong Jin Woo; Moon Ho Suh; Eun Seob Shin; Chan-Woo Lee; Suck-Hyun Lee (71-74).
The electrorheological (ER) properties of poly(2-dodecyloxyaniline) (PDOA) suspensions in silicone oil were investigated. The ER behavior of such suspensions of polyaniline particles depends on the type of stabilizer and doping or dedoping level. Here we report on the ER behavior of particles of a substituted polyaniline with long alkyl pendants. Rheological measurements were carried out using a rotational rheometer with high-voltage generator in both constant shear stress and rate modes. Suspensions of the as-synthesized polyaniline particles in silicone oil showed a substantial ER response.
Keywords: Electrorheological fluid; Polyaniline; Electric field;

Film formation from monodisperse acrylic latices by Shiva Zohrehvand; Klaas te Nijenhuis (75-82).
The influences of drying temperature, ageing time and ageing temperature on the film formation in coalescing agent containing latex films were investigated via turbidity measurements and atomic force microscopy. Coalescing agents used are 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate (TEX) and ethylene glycol monobutyl ether (EB). Latex films were dried at different temperatures. At a drying temperature of 40 °C, the differences in immersion patterns of neat and 1% coalescing agent containing latex films are too small to show significant improvement in film formation during 1 h of drying. Increase of the temperature from 40 to 50 °C, however, causes an improvement in film formation. At higher temperatures (95 °C), fast removal of the liquid phase cannot be prevented by the addition of 1% coalescing agent. Although addition of higher amounts of coalescing agent results in an increase of particle deformation and film surface smoothness, it intensifies also the water absorption of dried films. Ageing below the MFFT does not result in a significant improvement of film formation in the presence of 1% coalescing agent. Above the MFFT, coalescing agents act more efficiently and cause an improvement in film formation. By addition of higher amounts of coalescing agent the completion of the film formation process is delayed: for example, by the addition of 15% EB, nearly 1 year of ageing at room temperature is required for an efficient result.
Keywords: Acrylic latices; Film formation; Coalescing agents; Atomic force microscopy; Immersion patterns; Interference;

Preparation of helical peptide monolayer-coated gold nanoparticles by Nobuyuki Higashi; Jun Kawahara; Masazo Niwa (83-87).
We describe herein the preparation of polypeptide (poly(γ-benzyl-l-glutamate)) monolayer-covered gold nanoparticles (PBLG(n)SS–Au). Two types of PBLG(n)SS having PBLG segment length n = 20 and 50 were synthesized and successfully attached to the gold nanoparticle surface using the Brust–Schiffern method. The mean sizes of PBLG(n)SS–Au particles and their gold cluster cores in CHCl3, which were evaluated by means of dynamic light scattering and TEM, respectively, demonstrated that the gold cluster surfaces were covered with PBLG monolayers, and their conformation was found to be mainly in α-helix on the basis of FT-IR spectroscopy.
Keywords: Gold nanoparticle; Peptide; α-Helix; Monolayer; Gold plasmon;

Effect of the polar headgroup of phospholipids on their interaction with actin by T. Le Bihan; D. Pelletier; P. Tancrède; B. Heppell; J.P. Chauvet; C.R. Gicquaud (88-96).
It is generally admitted that actin filaments are anchored to a membrane by membranar actin-binding-proteins. However, we found that actin may also interact directly with membrane phospholipids. The actin–phospholipid complex has been investigated at the air–water interface using a film balance technique. In order to probe the effect of the phospholipid headgroup on the actin–phospholipid interaction, we focus mainly on phospholipids that have the same acyl chain length but different headgroups. For all the phospholipids, the apparent area per molecule (the total surface divided by the number of lipid molecules) increases after the injection of the protein into the subphase, which suggests an intercalation of actin between the phospholipid molecules. This effect seems to be more important for DMPE and DMPS than for DMPG, suggesting that the headgroup plays an important role in this intercalation. The critical surface pressure associated to the liquid expanded–liquid condensed (LE-LC) phospholipid transition increases with the concentration of G-actin and thus suggests that G-actin acts as an impurity, simply competing as a surfactant at the air–water interface. On the other hand, F-actin affects the LE to LC transition of phospholipids differently. In this case, the LE to LC transition is broader and F-actin slightly decreases the critical surface pressure, which suggests that electrostatic interactions are involved.
Keywords: Actin; Membrane; Actin–lipids interactions; Monolayers; Phospholipid binary mixture;

Self-assembly of synthetic hydroxyapatite nanorods into an enamel prism-like structure by Haifeng Chen; Brian H. Clarkson; Kai Sun; John F. Mansfield (97-103).
The application of surfactants as reverse micelles or microemulsions for the synthesis and self-assembly of nanoscale structures is one of the most widely adopted methods in nanotechnology. These synthesized nanostructure assemblies sometimes have an ordered arrangement. The aim of this research was to take advantage of these latest developments in the area of nanotechnology to mimic the natural biomineralization process to create the hardest tissue in the human body, dental enamel. This is the outermost layer of the teeth and consists of enamel prisms, highly organized micro-architectural units of nanorod-like calcium hydroxyapatite (HA) crystals arranged roughly parallel to each other. In particular, we have synthesized and modified the hydroxyapatite nanorods surface with monolayers of surfactants to create specific surface characteristics which will allow the nanorods to self-assemble into an enamel prism-like structure at a water/air interface. The size of the synthetic hydroxyapatite nanorods can be controlled and we have synthesized nanorods similar in size to both human and rat enamel. The prepared nanorod assemblies were examined using transmission electron microscopy (TEM) and atomic force microscopy (AFM). The specific Langmuir–Blodgett films were shown to be comprised of enamel prism-like nanorod assemblies with a Ca/P ratio between 1.6 and 1.7.
Keywords: Hydroxyapatite; Nanorod; Self assembly; Dental enamel;

In this study, the vertical motion of a particle in a quiescent fluid falling toward a horizontal plane wall is analyzed, based on simplified models. Using the distance between the particle and wall as a parameter, the effects of various forces acting on the particle and the particle motion are examined. Without the colloidal and Brownian forces being included, the velocity of small particles is found to be approximately equal to the inverse of the drag force correction function used in this study as the particle approaches the near-wall region. Colloidal force is added to the particle equation of motion as the particle moves a distance comparable to its size. It is found that the particle might become suspended above or deposited onto the wall, depending on the Hamaker constant, the surface potentials of the particle and wall, and the thickness of the electrical double layer (EDL). For strong EDL repulsive force and weaker van der Waals (VDW) attractive force, the particle will become suspended above the wall at a distance at which the particle velocity is zero. This location is referred to as the equilibrium distance. The equilibrium distance is found to increase with increased in EDL thickness when a repulsive force barrier appears in the colloidal force interaction. For the weak EDL repulsive force and strong VDW attractive force case, the particle can become deposited onto the wall without the Brownian motion effect. The Brownian jump length was found to be very small. Many Brownian jumps would be required in a direction toward the wall for a suspended particle to become deposited.
Keywords: Colloidal force; Electrical double layer; Equilibrium distance; Brownian jump; Particle deposition;

Core-shell silica particles, with a diameter of 1.5 μm, containing a dye fluorescein isothiocyanate (FITC), are synthesized by the hydrolysis and condensation of tetraethylorthosilicate (TEOS). Sodium dodecyl sulfate (SDS) is added to synthesize fluorescent core particles with the diameter of approximately 1 μm. In the addition of SDS, the surface charge reduced by counterions (Na+) of the surfactant leads to a higher degree of aggregation of the primary particles and the formation of larger secondary particles. The particle growth kinetics confirms the aggregation growth model for the synthesis of monodisperse silica particles, and also shows the dependence of final particle size on colloidal stability resulting from the addition of SDS. Light and X-ray scattering data reveal that the final particles have compactly packed structures with smooth surfaces. The seeded growth technique is then used to form a silica shell layer on the fluorescent core. The added amount of water and NH4OH has significant effects on shell formation. Finally, the final core-shell silica particles are modified by chemisorption of octadecanol at the surface to be dispersed in organic solvents. Octadecyl-coated silica particles are sterically stabilized in silica index-matching solvents such as chloroform and hexadecane to directly image separate particles using confocal microscopy. In chloroform, the organophilic silica particles disperse well, whereas in hexadecane they form a volume-filling gel structure at room temperature.
Keywords: Silica particle; Stöber method; Sodium dodecyl sulfate (SDS); Aggregation mechanism; Internal structure; Confocal microscopy;

Shifts in polystyrene particle surface charge upon adsorption of the Pluronic F108 surfactant by Rik ter Veen; Karin Fromell; Karin D. Caldwell (124-128).
Electrical field-flow fractionation (ElFFF) and sedimentation field-flow fractionation (SdFFF) were used in combination to study the adsorption of the triblock polymeric surfactant, Pluronic F108 [(EO)129-(PO)56-(EO)129] to 200 nm polystyrene (PS) latex spheres. The SdFFF technique allowed an accurate determination of the mass of surfactant adsorbed on each particle from a solution of given concentration. To complement this isotherm study, we show that ElFFF can be used to measure fractional coverages of the formed electrically neutral surfactant layers on the charged PS particles. Through a combination of the two techniques it is possible to gain information about the structure of the adsorbate layer. Thus, when Pluronic F108 is taken up by the PS surface from solutions of low concentration, all three blocks appear to adhere to the surface as long as there is free space available. As the solution concentration increases and the fractional coverage reaches approximately 20%, the surface turns crowded enough to let the strongly adsorbing PPO blocks competitively displace the weakly adherent PEO blocks, which gradually rise to extend into the aqueous phase until the surface is fully saturated.
Keywords: Sedimentation field-flow fractionation; Electric field-flow fractionation; Pluronic adsorption; Polystyrene lattices; Competitive adsorption;

The behaviour of micro-bitumen drops in aqueous clay environments by Christina Tsamantakis; Jacob Masliyah; Anthony Yeung; Thomas Gentzis (129-139).
This study summarises the rheological behaviour of emulsion bitumen drops in the presence of aqueous solutions of de-ionised or process water (DIW or PW) containing montmorillonite clays (M) and/or calcium ions (Ca++). The presence of calcium ions and montmorillonite clays resulted in the plastic behaviour of bitumen drops. In a DIW + M + Ca++ system, increasing temperature and calcium ion concentration resulted in an increase in the number and degree of plastic bitumen drops. In the presence of considerable amounts of Ca++ ions and/or at higher experimental temperature, bitumen drops in a PW + M system exhibited no significant overall plasticity of their surfaces. Both calcium and sodium ions contained in process water compete with each other to occupy the montmorillonite clay surface. At the pH value of process water (pH≅8), increasing the temperature did not change the value of bitumen droplet zeta potential. Stability of bitumen-in-water emulsions at 22 °C showed that bitumen droplets coalesced upon contact in the DIW + M system. The addition of calcium ions (Ca++) led to the inhibition of coagulation and coalescence of bitumen droplets, which may indicate the formation of CaM aggregates at the bitumen–water interface.
Keywords: Micropipette; Aqueous clay emulsions; Athabasca bitumen; Canada;

Synthesis and characterisation of Gd2O3 nanocrystals functionalised by organic acids by Fredrik Söderlind; Henrik Pedersen; Rodrigo M. Petoral; Per-Olov Käll; Kajsa Uvdal (140-148).
Nanocrystals of Gd2O3 have been prepared by various methods, using, e.g., trioctylphosphine oxide (TOPO), diethylene glycol (DEG) or glycine. The crystalline particles were of sizes 5 to 15 nm. Different carboxylic acids, e.g., oleic acid or citric acid, were adsorbed onto the surface of the particles made with DEG. IR measurements show that the molecules coordinate to the Gd2O3 surface via the carboxylate group in a bidentate or bridging manner. The organic-acid/particle complexes were characterised by XRPD, TEM, FTIR, Raman, and XPS.
Keywords: Nanocrystals; Synthesis; Functionalisation; IR; XPS;

Silica-modified titanium dioxides were prepared by a hydrothermal method and then characterized by XRD, FT-IR, XPS, TEM, and UV–visible spectroscopy. The silica-modified titanium dioxides were in anatase phase and had large surface areas. There was strong interaction between SiO2 and TiO2, and Ti―O―Si bonds formed during the hydrothermal process. The addition of silica in TiO2 particles could effectively suppress the formation of the rutile phase and the growth of titanium dioxide crystals. DRS spectra proved an increase in the band-gap transition with the increase of silica. The silica-modified TiO2 nanoparticles exhibited better photocatalytic activity, which increased with the silica amount, in comparison with pure TiO2 nanoparticles. Due to better thermal stability, the photocatalytic activity of the silica-modified TiO2 sample held good photocatalytic activity even after calcined at 1273 K.
Keywords: Titanium dioxide; Silica; Hydrothermal; Anatase; Photocatalytic;

Phase behavior of block co-poly(ethylene oxide–butylene oxide), E18B9 in water, by small angle neutron scattering by Alexander I. Norman; Derek L. Ho; Alamgir Karim; Eric J. Amis (155-165).
We present a small angle neutron scattering (SANS) study into the micellar structures of diblock copolymer E18B9 (where E denotes a ethylene oxide unit and B denotes a butylene oxide unit, 18 and 9 being the number of repeat units respectively) in aqueous solution over a range of five different concentrations (0.2, 1.0, 10.0, 20.0, and 40.0% (by mass fraction)) and eight temperatures (10 to 90 °C). The NG7 30 m SANS instrument provides a q range of 0.0009 to 0.5548 Å−1, thus probing the structure over a very broad length scale. At low temperature and low concentration, spherical micelles exist, elongating into worm-like structures at higher temperatures. This transition is observed by the scaling of the scattered intensity at low q and confirmed upon fitting to an appropriate model. Upon increasing concentration, the micelles pack into ordered arrays of either hexagonally packed rod-like micelles or lamellar sheets, again dependent on temperature. Both concentration and temperature effects of this block copolymer have been discussed.
Keywords: Micelles; SANS; Block copolymers; PDDF; Aqueous;

The interaction of silica and kaolin with dipalmitoylphosphatidylcholine (DPPC) has been studied using 13C and 31P solid state nuclear magnetic resonance spectroscopy. These studies explore the molecular interactions of these respirable dusts with a model lung surfactant species to characterize silica toxicity in mixed systems. The choline head group of DPPC was found to remain mobile when adsorbed on kaolin, in contrast to an immobile head group on silica. Further, glycerol carbon intensities were greatly diminished relative to that of choline carbons, a result attributed to broadening effects. These preliminary findings suggest that silica toxicity may not be related to choline mobility as previously noted [J. Colloid Interface Sci. 172 (1995) 536–538].
Keywords: DPPC; Silica; Kaolin; NMR; Silicosis; Lung surfactant; Silanol; Respirable dust; Dipalmitoylphosphatidylcholine;

Grafting of swelling clay materials with 3-aminopropyltriethoxysilane by Hongping He; Jannick Duchet; Jocelyne Galy; Jean-François Gerard (171-176).
The grafting reaction between a trifunctional silylating agent and two kinds of 2:1 type layered silicates was studied using FTIR, XRD, TGA, and 29Si CP/MAS NMR. XRD patterns clearly indicate the introduction of 3-aminopropyltriethoxysilane (γ-APS) into the clay interlayer. In the natural montmorillonite, γ-APS adopts a parallel-bilayer arrangement, while it adopts a parallel-monolayer arrangement in the synthetic fluorohectorite. These different silane arrangements have a prominent effect on the mechanism of the condensation reaction within the clay gallery. In natural montmorillonite, the parallel-bilayer arrangement of γ-APS results in bidentate (T2) and tridendate (T3) molecular environments, while the parallel-monolayer arrangement leads to monodentate (T1), as indicated by 29Si CP/MAS NMR spectra. This study demonstrates that the silylation reaction and the interlayer microstructure of the grafting products strongly depend on the original clay materials.
Keywords: 3-Aminopropyltriethoxysilane; Natural montmorillonite; Synthetic fluorohectorite; Grafting; X-ray diffraction; Thermogravimetric analysis; 29Si CP/MAS NMR;

Au/TiO2 nanocomposites have been prepared by UV photolysis or chemical reduction of a Au(III) complex formed on a spherical or a rodlike TiO2 support, and their catalytic activity for 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging reaction was investigated. The chemical reduction with dimethylamine borane (DMAB) provided smaller gold nanoparticles than those synthesized by UV photolysis. Type of the TiO2 also affected the size of gold particles; smaller gold particles were deposited on the spherical TiO2 support than on rodlike one. For the radical scavenging reaction, the Au/TiO2 nanocomposites prepared by chemical reduction exhibited a higher catalytic activity than those photochemically prepared, and rodlike TiO2 provided a higher activity than spherical one. The effects of preparation methods and type of TiO2 supports on the catalytic activity are discussed.
Keywords: Gold; TiO2; DPPH; Dimethylamineborane; Nanocomposites; UV photolysis; Catalysis; Radical scavenging reaction;

Nanostructured TiO2 ultrafine powder (Ti-SG) 100% anatase phase prepared by the sol–gel method was used as a photocatalyst in the decomposition reaction of a basic dye, Crystal Violet (hexamethyl-p-rosaniline chloride), in water under UV light irradiation. Optimization of the photocatalyst's performance as a function of irradiation time, catalyst concentration, and solution pH was performed. The photoactivity was greatly dependent on the solution pH and it was effective for Crystal Violet to be degraded under basic conditions. The extent of photooxidation or -reduction of CV was discussed in terms of the Langmuir–Hinshelwood model. Results also indicated that the proper addition of H2O2 could improve the degradation rate, but excess H2O2 quenched the formation of OH. Textural and photocatalytic characteristics of sol–gel derived TiO2 (Ti-SG) were compared with those of commercial P25, TiO2. The relative photonic efficiency of sol–gel derived TiO2 was found to be 2.77 with reference to phenol.
Keywords: Nanocrystalline TiO2; Sol–gel; Crystal Violet; UV illumination; Photodegradation; H2O2;

Scanning tunneling microscopy (STM) and noncontact tapping mode atomic force microscopy (AFM) have been employed to study on a local scale the structural and, for the first time, the chemical changes of carbon black (CB) particles following plasma oxidation. STM imaging of the pristine, untreated particles revealed a relatively ordered structure of tiny crystallites with a few amorphous regions. After plasma treatment, the crystallites were no longer observed and the CB particle surface exhibited a noticeable and ubiquitous increase in atomic-scale disorder. Phase contrast images obtained with noncontact tapping mode AFM indicated that the untreated CB particles were essentially hydrophobic as a pristine basal surface of graphite, but with occasional hydrophilic patches. By contrast, their plasma-treated counterparts displayed enhanced hydrophilicity as a result of the introduction of oxygen onto the CB surface, the presence of which was evidenced by X-ray photoelectron spectroscopy, but most significantly, such enhancement was observed to be quite uniform at a local scale of individual particles. The possibility of investigating on a very local scale the chemical behavior of oxidized CB particles should be useful for the control and optimization of their dispersion properties in different systems.
Keywords: Carbon black; Atomic force microscopy; Scanning tunneling microscopy; Oxidation;

Nanocomposite based on poly(N-octadecyl-2-ethynylpyridinium bromide) and Mg0.04Nb1.66O5 nanosheets by G.K. Prasad; T. Takei; Y. Yonesaki; N. Kumada; N. Kinomura (200-204).
A novel nanocomposite based on poly(N-octadecyl-2-ethynylpyridinium bromide) (PNOEtPyBr) and Mg0.04Nb1.66O5 nanosheets is synthesized by the method of exfoliation–reflocculation. The XRD data of the nanocomposite indicates the formation of Mg0.04Nb1.66O5 nanosheets/PNOEtPyBr nanostructure with an interlayer expansion of 4.6 nm along a direction perpendicular to the Mg0.04Nb1.66O5 nanosheets. Formation of this nanocomposite is further supported by the results obtained by FT-IR spectroscopy and thermogravimetry. This nanocomposite exhibits interesting dielectric properties with a dielectric constant of 18.7 F/m at 1000 Hz and 25 °C, which are also compared to the properties of HMg0.34Nb1.66O5 and PNOEtPyBr.
Keywords: Nanocomposite; Exfoliation; Reflocculation; Nanosheets; Dielectric constant;

Reversible adsorption inside pores of ultrafiltration membranes by N.V. Churaev; R.G. Holdich; P.P. Prokopovich; V.M. Starov; S.I. Vasin (205-212).
A range of experiments were performed on the dead-end ultrafiltration (UF) of poly(ethylene glycol) (PEG) of different molecular weights. Deviations from a linear dependence of the filtration rate with the applied membrane pressure difference were found. It is shown that these deviations are not caused by an osmotic pressure influence but determined by the reversible adsorption of PEG molecules inside the pores of the ultrafiltration membranes used. A theoretical model of the process is suggested, which describes the reversible adsorption inside the membrane pores and the corresponding reduction of the filtration velocity. Comparison of the theory predictions with experimental data on the ultrafiltration of PEG shows a good agreement between the theoretical predictions and experimental data. A theory is presented for calculation of the PEG rejection coefficient in the case of ultrafiltration.
Keywords: Reversible adsorption; Ultrafiltration; Permeability;

Dynamic wetting: Hydrodynamic or molecular-kinetic? by Srinivas R. Ranabothu; Cassandra Karnezis; Lenore L. Dai (213-221).
The dynamic wetting behavior of simple liquids (water, glycerin, formamide, ethylene glycol, and a mixture of water and ethylene glycol) and polydimethylsiloxane (PDMS) oils with different viscosities has been investigated. The hydrodynamic, molecular-kinetic, and combined molecular-hydrodynamic models have been applied to the experimental results to evaluate the models' adequacy. Our work suggests that the molecular displacement, i.e., the adsorption and desorption process, seems to be dominant for the simple liquids investigated. For polydimethylsiloxanes, our work suggests that none of the evaluated models is sufficient to explain the experimentally observed dependence of the dynamic contact angle on contact velocity. This work, to the best of our knowledge, provides the first extensive comparison of the three models with experimental data over a wide range of viscosity. In addition, we have investigated the contact angle hysteresis and conclude that it is a strong function of the contact speed, the interactions between the fluids and the substrate, and the fluid viscosity.
Keywords: Contact angles; Dynamic wetting; Hydrodynamic model; Molecular-kinetic model; Combined model; Contact angle hysteresis;

Effects of confined geometry on phase-separated dextran/gelatine mixtures exposed to shear by Camilla Lundell; Els H.A. de Hoog; R. Hans Tromp; Anne-Marie Hermansson (222-229).
The effect of shear on aqueous phase-separated dextran/fish gelatine mixtures with a total concentration of 5 and 10% was studied in a confined geometry. It was measured as a function of composition, strain rate and gap size. This was done by using both small-angle light scattering and a shear cell combined with a confocal laser scanning microscope. At a total polymer concentration of 5%, small-angle light scattering results showed that up to 100   s −1 the deformation of the domains increases with the strain rate. At strain rates less than 100   s −1 , the response of the system to strain is dominated by strain rate-dependent deformation. At a higher strain rate there might be balance between break-up and re-coalescence. At a total concentration of 10%, small effects of the gap size were found. In confined geometry, the coalescence rate was faster than expected from viscous hydrodynamic growth. The microscope images showed that the gelatine-enriched phase forms a wetting layer on the surface of the glass wall. The degree of wetting appears to increase with increasing the strain rate up to 60   s −1 and decreases again at higher strain rates.
Keywords: Phase separation; Shear; Small-angle light scattering; Confocal laser scanning microscope; Gelatine; Dextran;

Structure of AOT reverse micelles under shear by Hadas Gochman-Hecht; Havazelet Bianco-Peled (230-237).
Reverse micelles in the AOT/water/isooctane system, at various water contents ( W 0 ) , were studied using rheometry and small angle X-ray scattering (SAXS) experiments under static conditions and under shear. The SAXS analysis confirmed the spherical shape of the micelles at low water content and revealed a transition into elongated micelles at higher water content. A population of spherical micelles was found to coexist with the cylindrical ones, even above the percolation threshold. The shape transformation was correlated with a viscosity leap observed in the rheometry measurements. Reverse micelles at low water content under shear act as a Newtonian fluid, without any detectable shape changes. In contrast, reverse micelles at high water content behave as a shear thinning fluid. SAXS measurements at high water content under shear force have shown that the shear forces induced alignment of the cylindrical micelles in the flow direction, without any other changes in the micelle dimensions. The anisotropy parameter, a measure of the degree of the spatial order, was found to increase with increasing water content and shear rate.
Keywords: AOT reversed micelles; Small-angle X-ray scattering; Rheology; Shear-induced alignment; Shear thinning;

Critical micelle concentrations and interaction parameters of aqueous binary surfactant:ionic surfactant mixtures by Hideo Akisada; Junko Kuwahara; Kouji Noyori; Ryobun Kuba; Takashi Shimooka; Atsuko Yamada (238-246).
A relationship between the critical micelle concentration (CMC) and the surfactant's composition in the bulk phase that supercedes Rubingh's method is derived for aqueous mixtures of ionic surfactants by considering the interaction between a micellar ionic aggregate and the diffusion layer around it. To test this approach we measured the CMCs of solutions of cationic surfactant mixtures and also of alkylammonium dodecanesulfonate mixtures. In the absence of controlled concentration of the counterion, the CMCs do not fit Clint's equation, but CMCs measured at a constant counterion concentration fit it approximately. The interaction parameter in the theory of regular solutions is obtained from the relationship between the micellar and bulk compositions. The values of the interaction parameter and the concentration exponent change with the hydrophobicity of the counterion in mixtures of alkylammonium dodecanesulfonates. The micellar composition of dodecylammonium chloride and dodecyltrimethylammonium chloride mixtures depends very little on the counterion concentration. The interaction energy between the ammonium and trimethylammonium groups of the cationic surfactants is about − 0.05 kT on average and depends on the concentration of the counterion.
Keywords: Ionic surfactant; Mixture; Mixed micelle; Head group; Counterion; Chain length; Interaction; Regular solution; Micellar composition;

A comparative study of the physicochemical properties of perfluorinated and hydrogenated amphiphiles by Elena Blanco; Alfredo González-Pérez; Juan M. Ruso; Rosa Pedrido; Gerardo Prieto; Félix Sarmiento (247-260).
In this work we studied and compared the physicochemical properties of perfluorinated (sodium perfluoroheptanoate, C7FONa, and perfluorooctanoate, C8FONa) and hydrogenated (sodium octanoate, C8HONa, decanoate, C10HONa, and dodecanoate, C12HONa) amphiphiles. First, we determined their Krafft points to study the solubility and appropriate temperature range of micellization of these compounds. The critical micelle concentration (cmc) and ionization degree of micellization (β) as a function of temperature (T) were estimated from conductivity data. Plots of cmc vs T appear to follow the typical U-shaped curve with a minimum T min . The results show that the surfactants with CF2/CH2 ratio of 1.5 between alkyl chains (C12HONa–C8FONa and C10HONa–C7FONa) have nearly the same minimum value for cmc against temperature. The comparison between the cmc of hydrogenated amphiphiles and the corresponding perfluorinated amphiphiles must be done at this point. Thermodynamic functions of micellization were obtained by applying different theoretical models and choosing the one that best fit our experimental data. Although perfluorinated and hydrogenated amphiphiles present similar thermodynamic behavior, we have found a variation of 1.3 to 1.7 in the CF2/CH2 ratio, which did not remain constant with temperature. In the second part of this study the apparent molar volumes and adiabatic compressibilities were determined from density and ultrasound velocity measurements. Apparent molar volumes at infinite dilution presented the ratio 1.5 between alkyl chains again. However, apparent molar volumes upon micellization for sodium perfluoroheptanoate indicated a different aggregation pattern.
Keywords: Perfluorinated; Hydrogenated; Krafft point; Thermodynamics; Critical micelle concentration minimum;

Solubilization of water in mixed reverse micellar systems with anionic surfactant (AOT) and nonionic surfactants (Brijs, Spans, Tweens, Igepal CO 520), cationic surfactant (DDAB)–nonionic surfactants (Brijs, Spans, Igepal CO 520), and nonionic (Igepal CO 520)–nonionics (Brijs, Spans) in oils of different chemical structures and physical properties (isopropyl myristate, isobutyl benzene, cyclohexane) has been studied at 303 K. The enhancement in water solubilization has been evidenced in these systems with some exceptions. The maximum water solubilization capacity ( ω 0 , max ) in mixed reverse micellar systems occurred at a certain mole fraction of a nonionic surfactant, which is indicated as X nonionic , max . The addition of electrolyte (NaCl or NaBr) in these systems tends to enhance their solubilization capacities further both at a fixed composition of nonionic ( X nonionic ; 0.1) and at X nonionic , max at 303 K. The maximum in solubilization capacity of electrolyte ( ω max ) was obtained at an optimal electrolyte concentration (designated as [NaCl]max or [NaBr]max). All these parameters, ω 0 , max vis-à-vis X nonionic , max and ω max vis-à-vis [NaCl]max, have been found to be dependent on the surfactant component (content, EO chains, and configuration of the polar head group, and the hydrocarbon moiety of the nonionic surfactants) and type of oils. The conductance behavior of these systems has also been investigated, focusing on the influences of water content (ω), content of nonionics ( X nonionic ), concentration of electrolyte ([NaCl] or [NaBr]), and oil. Percolation of conductance has been observed in some of these systems and explained by considering the influences of the variables on the rigidity of the oil/water interface and attractive interactions of the surfactant aggregates. Percolation zones have been depicted in the solubilization capacity vs X nonionic or [electrolyte] curves in order to correlate with maximum in water or electrolyte solubilization capacity. The overall results, obtained in these studies, have been interpreted in terms of the model proposed by Shah and co-workers (Langmuir 3 (1987) 1086; J. Colloid Interface Sci. 120 (1987) 320 and 330) for the solubility of water in water-in-oil microemulsions, as their model proposed that the two main effects that determine the solubility of these systems are curvature of the surfactant film separating the oil and water and interactions between water droplets.
Keywords: Solubilization; Mixed reverse micelles; AOT; DDAB; Brijs; Isopropyl myristate; Percolation of conductance;

Isotherms of binding of dodecylpyridinium chloride (DPC) and cetylpyridinium chloride (CPC) by copolymers of maleic acid (MA; degree of neutralization=1) with methyl methacrylate (MMA), styrene (St), and vinyl acetate (VA) were determined at various salt concentrations by using the potentiometric technique. The average composition of copolymers corresponds to designations MA(MMA)3, MASt, and MAVA. Very different binding behavior has been found. The cooperativity parameter, u, for binding to MA(MMA)3 is the lowest and displays no dependence on ionic strength, which is a consequence of significant hydrophobic polymer–surfactant interactions. Isotherms for the DPC/MASt system display a two-step binding mechanism, which could not be clearly identified in the CPC/MASt case, presumably due to interference of surfactant micellization with the second step. It is proposed that the first step of binding in DPC/MA(MMA)3 and in DPC/MASt solutions is of electrostatic origin, as is the second step in DPC/MASt. On the contrary, the second step in DPC/MA(MMA)3 is mostly due to hydrophobic interactions of surfactant hydrocarbon tails with the predominantly uncharged DPC/MA(MMA)3 complex. MAVA solutions display the highest critical aggregation concentration (cac) values, which show a slight decreasing trend with increasing ionic strength. The very compact form of the MAVA copolymer at high salt content was responsible for this.
Keywords: Cationic surfactants; Maleic acid copolymers; Neutral comonomer unit; Polyelectrolyte–surfactant interactions;

Transient response of an electrorheological fluid under square-wave electric field excitation by Yu Tian; Cuihong Li; Minliang Zhang; Yonggang Meng; Shizhu Wen (290-297).
The transient process of an electrorheological (ER) fluid based on zeolite and silicone oil sheared between two parallel plates to which a square-wave electric field is applied has been experimentally studied. The transient shear stress response to the strain or time is tested. The characteristic constants of time under different applied electric fields and shear rates have been determined. The response time is found to be proportional to shear rate with an exponent of about −0.75 in the tested shear rate range, which agrees with the theoretical predictions made by others. But it only shows a small dependence on the strength of the applied electric field. The results show that the transient process of ER fluids is related to the structure formation in the shearing. When the required shear strain is reached, the shear stress rises to a stable value under constant electric field. Although the electric field strength greatly affects the yield strength, it shows little effect on the stress response time. Also, experiments showed the electric field-induced shear stress decreased with an increase of shear rate.
Keywords: Electrorheological fluid; Parallel plates; Characteristic time constant; Electric field strength; Shear rate;

Fe2O3 and Fe2O3/SiO2 hollow spheres with tailored dimensions and compositions were created by consecutively coating polystyrene (PS) latices either with Fe3+ alternately adsorbed with Nafion or combining a sol–gel process based on the hydrolysis of tetraethoxysilane (TEOS), and subsequently removing the cores upon pyrolysis.
Keywords: Hollow sphere; Layer-by-layer self-assembly; Iron oxide; Silica; Sol–gel process; Nafion;

Highly concentrated, well-stable gold colloids can be prepared directly from an amine-bearing polyelectrolyte–HAuCl4 aqueous solution at room temperature. It is found that increasing molar ratio of polyelectrolyte to gold leads to increasing particle size. UV–vis spectra, transmission electron microscopy (TEM), and X-ray photoelectron spectra (XPS) were used to characterize the products thus formed.
Keywords: Highly concentrated gold colloids; Room temperature; Polyelectrolyte;

Precision in transient electric birefringence measurements for colloids by B.R. Jennings; P.J. Rudd; D.R. Waterman (304-307).
Electrically induced birefringence is increasingly used as a fast procedure to characterise the size, shape, polarisation and charge parameters of colloids and their interactions. By considering the optical apparatus generally used, attention is drawn to the significant errors that can arise in such experiments if optical component selection and setting are not critically considered.
Keywords: Optical Kerr effect; Birefringence measurement; Colloid characterisation; Measurement errors;

Size dependence is imparted onto a modified bridge functional, adopted for a recently proposed semi-analytical hard sphere reference system theory for calculation of solvent-mediated potential (SMP). The SMP for two large hard sphere particles immersed in a small hard sphere solvent bath predicted by the present improved version is in satisfactory agreement with the prediction from a theoretically based fitting formula. Isostructural solid–solid transitions in the binary asymmetrical hard sphere system are investigated based on a single-component macrofluid approximation combined with the improved version. It is found that the isostructural solid–solid transition appears when size asymmetry increases. The limiting asymmetry size ratio is near 1 / 8 . As the size asymmetry increases, critical density for both large and small hard sphere components for the fcc isostructural solid–solid transition increases and decreases, respectively.
Keywords: Binary hard sphere mixture; Potential of mean force; Density functional theory;

Influence of the reactant concentrations on the synthesis of ZnO nanoparticles by Zeshan Hu; José F. Herrera Santos; Gerko Oskam; Peter C. Searson (313-316).
We report on the synthesis of ZnO nanoparticles from Zn(CH3CO2)2 and NaOH in 2-propanol. Nucleation and growth are fast, and hence at longer times the particle size is controlled by coarsening. The coarsening kinetics are independent of the Zn(CH3CO2)2 concentration between 0.5 and 1.25 mM at a fixed [Zn(CH3CO2)2]:[NaOH] ratio of 0.625. The width of the size distribution was found to increase only slightly with aging time. In addition, at a fixed Zn(CH3CO2)2 concentration of 1 mM, the kinetics are independent of the [Zn(CH3CO2)2]:[NaOH] ratio between 0.476 and 0.625. The presence of water in the reaction mixture was found to only slightly affect the coarsening kinetics for water contents larger than about 20 mM. For lower water concentrations, the nucleation and growth of ZnO were very slow. It can be concluded that the synthesis method described provides a reliable source of ZnO nanoparticles due to its insensitivity to the reactant concentrations and the presence of water.
Keywords: Coarsening; Nanoparticles; Metal oxide; Zinc oxide;

by Arthur Hubbard (317).