Journal of Colloid And Interface Science (v.313, #1)

On the transport of emulsions in porous media by Andrea Cortis; Teamrat A. Ghezzehei (1-4).
Emulsions appear in many subsurface applications including bioremediation, surfactant-enhanced remediation, and enhanced oil-recovery. Modeling emulsion transport in porous media is particularly challenging because the rheological and physical properties of emulsions are different from averages of the components. Current modeling approaches are based on filtration theories, which are not suited to adequately address the pore-scale permeability fluctuations and reduction of absolute permeability that are often encountered during emulsion transport. In this communication, we introduce a continuous time random walk based alternative approach that captures these unique features of emulsion transport. Calculations based on the proposed approach resulted in excellent match with experimental observations of emulsion breakthrough from the literature. Specifically, the new approach explains the slow late-time tailing behavior that could not be fitted using the standard approach. The theory presented in this paper also provides an important stepping stone toward a generalized self-consistent modeling of multiphase flow.A novel CTRW based model for emulsion transport provides an excellent match to the experimental oil breakthrough curve of Coulibaly et al. [K.M. Coulibaly, R.C. Borden, J. Control. Hydrol. 71 (1–4) (2004) 219–237].
Keywords: Emulsion; Porous media; Colloidal transport; Memory effects;

Characterization and pillaring of a Turkish bentonite (Resadiye) by A. Tabak; B. Afsin; B. Caglar; E. Koksal (5-11).
The shifts of the Si―O―Si stretching and the Si―O―Al and Si―O―Si bending modes, as well as the free silica peak in the IR spectra and the strengthening of the XRD reflections due to the quartz and α-cristobalite components of the Al-pillared bentonites (Wyoming and Resadiye), are ascribed to the formation of new Si―O―Al groups of covalent character. The mass losses in the temperature range 150–700 °C correspond to the dehydration and dehydroxylation processes. The total mass losses of the Al-pillared bentonites (Wyoming and Resadiye) are close to each other at an OH/Al ratio of 2.2, but calcination from 400 to 600 °C causes the surface area of the latter composite to decrease by 13%.The shifts of the Si―O―Si stretch and the Si―O―Al and Si―O―Si bending modes in the IR spectra, the characteristic XRD reflections, and the surface area decrease by 13% upon calcination up to 600 °C of Al-pillared bentonite (Resadiye) are all evidence for the formation of oxocationic pillar props.
Keywords: Al-pillared bentonites; Thermal stability; Basal spacing; Cation exchange capacity; Microporous composite; FTIR;

CO2 and N2 adsorption kinetics and equilibrium behaviours have been studied with silicalite, NaY and 13X by using concentration pulse chromatography for the separation of these gases in the present study. Adsorption Henry's Law constants, the heat of adsorption values, micropore diffusion coefficients and corresponding activation energies are determined experimentally and the three different mass transfer mechanisms are discussed. From the equilibrium data, the corresponding separation factors are obtained for the adsorption separation processes. The heat of adsorption values as well as the Henry's Law adsorption equilibrium constants of CO2 are much higher than those of N2 for all the adsorbents studied. 13X, NaY and silicalite all have good separation factors for CO2/N2 system based on equilibrium processes. The order of the equilibrium separation factors is 13X (Ceca) > 13X (Zeochem) > NaY (UOP) ≫ silicalite (UOP). Equilibrium selectivity favours CO2 over N2. Micropore diffusion resistance is the definite dominant mass transfer mechanism for CO2 with silicalite and NaY.Worldwide atmospheric carbon dioxide levels.
Keywords: Adsorption of carbon dioxide; Adsorption of nitrogen; Flue gas separation; Silicalite; NaY; 13X; Henry's Law constant;

Surface properties of two different phases of alumina were studied through SEM images. Characterization of amorphous acidic alumina and crystalline boehmite by XRD explains the differences in adsorption capacities of each sample. Data from small angle neutron scattering (SANS) provide further results regarding the ordering in amorphous and crystalline samples of alumina. Quantitative measurements from SANS are used for pore size calculations. Higher disorder provides more topological traps, irregularities, and hidden grooves for higher adsorption capacity. An isotherm model was derived for adsorption of dibenzothiophene sulfone (DBTO) by amorphous acidic alumina to predict and calculate the adsorption of sulfur compounds. The Langmuir–Freundlich model covers a wide range of sulfur concentrations. Experiments prove that amorphous acidic alumina is the adsorbent of choice for selective adsorption in the ultrasound-assisted oxidative desulfurization (UAOD) process to produce ultra-low-sulfur fuel (ULSF).A hybrid Langmuir–Freundlich isotherm model for DBTO adsorption on amorphous acidic alumina.
Keywords: Desulfurization; Langmuir–Freundlich isotherm; Alumina; Adsorption; Ultra-low-sulfur fuel;

Counterions in layer-by-layer films—Influence of the drying process by João M.C. Lourenço; Paulo António Ribeiro; Ana Maria Botelho do Rego; Maria Raposo (26-33).
The amount of counterions, measured by means of X-ray photoelectron spectroscopy (XPS), in layer-by-layer (LbL) films of poly(allylamine hydrochloride) (PAH) and poly(styrene sulfonate) (PSS), prepared from solutions with various NaCl concentrations, is shown to be greatly influenced by the film drying process: a smaller amount of counterions is observed in films dried after adsorption of each layer, when compared with films that were never dried during the film preparation. This is attributed to the formation of NaCl nanocrystals during the drying process which dissolve when the film is again immersed in the next polyelectrolyte solution. The presence of bonded water molecules was confirmed in wet films indicating that the counterions near the ionic groups are immersed in a water network. The number of counterions is dependent on the amount of salt in polyelectrolyte solutions in such a way that for a concentration of 0.2 M the relative amount of counterions attains saturation for both dried and wet samples, indicating that the process which leads the aggregation of counterions near of the ionic groups is not influenced by the drying process. Moreover, it is proven for wet samples that the increase in salt concentration leads to a decrease in the number of PAH ionized groups as predicted by the Muthukumar theory [J. Chem. Phys. 120 (2004) 9343] accounting for the counterion condensation on flexible polyelectrolytes.
Keywords: Layer-by-layer; Self-assembly; Counterions; Drying; Water network; Ionic network; Ionization degree;

In this paper we report on the synthesis, characterization, and adsorption properties of the first 3-amino-1,2,4-triazole-modified porous silsesquioxane (ATPS). The isotherms of adsorption of MX2 (M = Cu(II), Co(II); X = Cl, Br, ClO 4) by ATPS were studied in ethanol and aqueous solutions at 298 K. The results showed that there is a good fit between the experimental data and the Langmuir isotherm. The adsorption capacity in both solvents followed the sequence Cu(II) ≫ Co(II). The lowest adsorption for Co(II) should be related to the largest hydration volume, which obstructs the adsorption capacity of the surface, and consequently causes a decrease in the number of cations adsorbed. For the salts with different anions the sequence was MCl2  > MBr2  > M(ClO4)2 in both solvents. The low affinity for M(ClO4)2 toward the solid phase is a consequence of the poorer coordination ability of the ClO 4. Adsorptions from ethanol solutions were higher than those from aqueous solutions due to the higher polarity of water, which can more strongly solvate the solute and the basic sites on the surface. The following adsorption capacities (in mmol g−1) were determined: 0.24 (aq) and 0.84 (eth) for CuCl2, 0.09 (aq) and 0.16 (eth) for CuBr2, and 0.08 (aq) and 0.11 (eth) for Cu(ClO4)2; 0.02 (aq) and 0.07 (eth) for CoCl2, 0.02 (aq) and 0.06 (eth) for CoBr2, and 0.01 (aq) and 0.05 (eth) for Co(ClO4)2.Synthesis, characterization, and adsorption properties of the first 3-amino-1,2,4-triazole-modified porous silsesquioxane.
Keywords: Silsesquioxane; Modified silsesquioxane; Adsorption; Isotherms of adsorption;

Capillary condensation in pores with rough walls: A density functional approach by P. Bryk; W. Rżysko; Al. Malijevsky; S. Sokołowski (41-52).
The effect of surface roughness of slit-like pore walls on the capillary condensation of a spherical particles and short chains is studied. The gas molecules interact with the substrate by a Lennard-Jones ( 9 , 3 ) potential. The rough layer at each pore wall has a variable thickness and density and consists of a disordered quenched matrix of spherical particles. The system is described in the framework of a density functional approach and using computer simulations. The contribution due to attractive van der Waals interactions between adsorbate molecules is described by using first-order mean spherical approximation and mean-field approximation.Pore filled with an adsorbate (orange spheres). Green spheres are the matrix particles. (For interpretation of the references to color in this text, the reader is referred to the web version of this article.)
Keywords: Adsorption; Pore; Capillary condensation; Density functional theory; Quenched-annealed systems;

Synthesis and phosphate uptake behavior of Zr4+ incorporated MgAl-layered double hydroxides by Ramesh Chitrakar; Satoko Tezuka; Akinari Sonoda; Kohji Sakane; Kenta Ooi; Takahiro Hirotsu (53-63).
We synthesized Zr4+ incorporated MgAl-layered double hydroxides, Mg(AlZr)-LDH(A) (where A denotes a counteranion in the interlayer space and is expressed as CO3 for carbonate and Cl for chloride ions), with different molar ratios of Mg/(Al + Zr). Then we characterized their uptake behavior toward phosphate ions. CO3-type tertiary LDH materials synthesized at room temperature show low crystallinity, whereas the highly crystalline Cl-type tertiary LDH, [Mg0.68Al0.17Zr0.14(OH)2][Cl0.26⋅(CO3)0.04⋅1.24H2O], was synthesized for the first time using a hydrothermal treatment at 120 °C. The distribution coefficients ( K d ) of oxo-anions were measured with a mixed solution containing trace amounts of the anions. The selectivity sequences were Cl, NO 3  < SO2− 4  ≪ HPO2− 4 for CO3-type materials and SO2− 4  < HPO2− 4  <NO 3 for the crystalline Cl-type material. The uptake of phosphate ions from model wastewater (2.0 mg-P/dm3) and phosphate-enriched natural seawater (0.33 mg-P/dm3) was investigated in detail. The CO3-type materials have higher phosphate uptakes than the Cl-type materials. The maximum phosphate uptake of the CO3-type material with a molar ratio of Mg/(Al + Zr) of 3 is 30 mg-P/g at pH 8.7 with the wastewater, and 16 mg-P/g at pH 8.1 with the seawater, in contrast to the case of the usual binary MgAl-LDH(CO3): 10 mg-P/g with the wastewater and less than 1 mg-P/g with the seawater. The large uptake and high selectivity of the CO3-type tertiary LDH materials is well explained by complex formation of phosphate ions directly with Zr(IV) centers in the layers.(a) Ion exchange of HPO2− 4 with CO2− 3 in the interlayer space followed by cross-linking with two Zr(IV) centers in the neighboring layers liberating two OH ions, (b) while for H2PO 4, ion exchange is followed by bonding of each H2PO 4 ion with one Zr(IV) center in the layer.
Keywords: Layered double hydroxides; Phosphate; Seawater; Adsorption; Selectivity;

The interfacial properties at well-ordered short-chain alkanethiol monolayer–aqueous interfaces are probed to understand the water structure near a hydrophobic surface. Monolayers of hexanethiol on highly oriented gold substrates have been prepared by various methods such as adsorption from alcoholic solution of the thiol, adsorption from neat thiol, and potential-controlled adsorption. The compactness and crystallinity of the monolayer have been probed using reflection–absorption infrared spectroscopy (RAIRS), atomic force microscopy (AFM), quartz crystal microbalance (QCM), and electrochemical techniques. The presence of a thin layer of solvent with reduced density/dielectric constant (termed “drying transition”) close to the methyl groups is identified. This is based on reduced interfacial capacitance observed in the presence of an aqueous electrolyte solution as compared to the expected value for a well-ordered monolayer–aqueous interface. Atomic force microscopy allows the determination of the variation in the dielectric constant of the solvent medium as a function of distance from the monolayer head group. The thickness of the transition layer (interphase) is found to be approximately 2 nm. The phenomenon of drying transition is not unique to water; preliminary studies indicate that formamide, which has a two-dimensional hydrogen-bonded network, shows similar characteristics.
Keywords: Self assembled monolayer; Aqueous interface; Water structure; Force microscopy; Capacitance measurements; QCM;

Nitric acid, hydrochloric acid and EDTA were carefully chosen as desorbent to systematically evaluate the adsorption/desorption performance of the Pb2+-adsorbing fine microparticles of poly(m-phenylenediamine). The sorption/desorption efficiency was maximized by optimizing desorption condition including the desorbent concentration, contact time, and desorption mode. The variation of the solution pH with Pb2+ desorption was recorded to speculate the desorption mechanism. The practical reusability of the microparticles was elaborated through the sorption–desorption cycle experiments in an optimum condition. It was found that the desorption was very rapid with an equilibrium time of several minutes. A strong dependence of the desorbability on the species and concentration of the desorbents was observed. When 20 mM EDTA was chosen as the desorbent, the highest desorptivity was up to 94.2% that was much higher than those using nitric and hydrochloric acids. A successive sorption–desorption study employing nitric acid indicated that the microparticles could be simply regenerated and reutilized for more than 5 cycles together with Pb2+ re-adsorption efficiency of about 50% and accumulative Pb2+ adsorption capacity of up to 720.4 mg L−1. Facilely prepared, extremely chemoresistant and cost-effective PmPD microparticles would be potentially used for multicyclic sorption of lead ions from aqueous solution.Facilely prepared, extremely chemoresistant and cost-effective polyphenylenediamine microparticles possess high accumulative Pb2+ adsorbance and very rapid desorption of 94.2% and could be reutilized for more than 5 cycles.
Keywords: Polyphenylenediamine; Microparticle; Lead ion; Successive multicyclic sorption and desorption; Chemoresistant sorbent; Desorbent; Water purification;

Removal of 2,4-dichlorophenol from aqueous solution by static-air-activated carbon fibers by Jian-Ping Wang; Yong-Zhen Chen; Hui-Min Feng; Shu-Juan Zhang; Han-Qing Yu (80-85).
Static-air-activated carbon fibers (ACFs) with lotus-root-like axially porous structure were used to adsorb 2,4-dichlorophenol (2,4-DCP) from aqueous solution. The adsorption isotherm was evaluated in the pH range 3.0–11.0. Results indicated that both Langmuir and Redlich–Peterson adsorption isotherms were appropriate for describing the adsorption characteristics of 2,4-DCP at various pH values and that lower pH values were favorable for adsorption. The adsorption of 2,4-DCP was controlled by the synergetic effects of π – π interaction and electrostatic attraction, and the former was dominant. Breakthrough curve results showed that the 2,4-DCP removal efficiency increased with an increase in the empty-bed contact time (EBCT). An EBCT of 0.660 min was sufficient for the adsorption of 2,4-DCP onto ACF, indicating a high adsorption rate. Desorption experiment results revealed that the ACF saturated with 2,4-DCP could be regenerated effectively by a 0.001 M NaOH solution.More than 95% of 2,4-DCP was desorbed after the static-air-activated ACFs saturated by 2,4-DCP was were treated with 0.001 M NaOH for three times. The adsorption capacity of the regenerated ACFs for 2,4-DCP was of almost the same level as that of the initial ACFs. Effective application of the static-air-activated ACFs for 2,4-DCP adsorption could be realized readily.
Keywords: 2,4-Dichlorophenol; Activated carbon fiber; Adsorption; Desorption;

Characterization of poly(ethylene imine) layers on mica by the streaming potential and particle deposition methods by Zbigniew Adamczyk; Aneta Michna; Magdalena Szaraniec; Anna Bratek; Jakub Barbasz (86-96).
Deposition kinetics of polystyrene latex (averaged particle size of 0.66 μm) on mica covered by poly(ethylene imine) (PEI), a cationic polyelectrolyte having an average molecular mass of 75,000 g mol−1, was studied using the impinging-jet method. The hydrodynamic radius of PEI, determined by PCS measurements, was 5.3 nm. The electrophoretic mobility of PEI was measured as a function of pH for ionic strengths of 10−3 and 10 −2 M, which made it possible one to determine the amount of electrokinetic charge of the molecule and its zeta potential. Formation of the polyelectrolyte layer on mica was followed by measuring the streaming potential in the parallel-plate channel. From these measurements, the dependence of the apparent zeta potential of mica on the surface coverage of PEI was determined. The amount of adsorbed PEI on mica was calculated from the convective diffusion theory. These results were quantitatively interpreted in terms of the theoretical model postulating a particle-like adsorption mechanism for PEI with not too significant shape deformation upon adsorption. On the other hand, the Gouy–Chapman model postulating the adsorption in the form of flat disks was proved inappropriate. After the surface was fully characterized, particle deposition experiments were carried out with the aim of finding the correlation between the polymer coverage and the initial rate of latex particle deposition. In the range of small polyelectrolyte coverage, a monotonic relation between the polymer coverage and the initial deposition rate of particles, as well as the jamming coverage, was found. For Θ PEI > 0.25 , the initial particle deposition rate attained the value predicted from the convective diffusion theory for homogeneous surfaces. These results were interpreted theoretically by postulating that an effective immobilization of colloid particles occurred on local polyelectrolyte assemblages containing between two and three PEI molecules.Precise determination of polyelectrolyte coverage on surfaces by the streaming potential method.
Keywords: PEI adsorption on mica; Particle deposition at polyelectrolyte layer; Streaming-potential measurements of PEI layer on mica; Electrophoretic mobility of PEI; Theoretical model for particle-like adsorption of PEI;

Tetrad effect in the adsorption of the lanthanides on zeolite Y by A. Gładysz-Płaska; M. Majdan; S. Pikus; W. Lewandowski (97-107).
The adsorption of the lanthanides (except for Pm) on the zeolite Y was investigated under various solution conditions of nitrate ion concentration ([NO 3]: 0.001–2 mol/dm3) and total lanthanide concentration (from 0.0001 to 0.001 mol/dm3). The solutions of the lanthanide nitrates were equilibrated with the zeolite samples at 296 K. The concentrations of lanthanides in the initial and equilibrium solutions were determined by means of spectrophotometrical method with Arsenazo III reagent and distribution constants K d of the lanthanides between aqueous and zeolite phases were calculated. The evident concave tetrad effect in the change of log K d values (nitrate concentrations 0.4–2 mol/dm3) within the lanthanide series was noticed and an attempt at its explanation through the comparison of covalence in Ln―O bonds existing in Al―O( 1 / 3 Ln )―Si species in the zeolite phase and in Ln(NO3)2+ complexes forming in the aqueous phase was presented. The weak convex tetrad effect for equilibrium nitrate concentrations 0.001–0.32 mol/dm3, manifesting in the change of log K d values and in the alteration of log K (adsorption constants), is evidence of the complexation of the tripositive lanthanide ions by the oxygens originating both from water molecules and from the zeolite framework.The tetrad effect in the adsorption constants K d of the lanthanides on the zeolite Y was observed, manifesting in the deviations from the straightline relationship log K d vs 1 / r (where r is the ionic radius of the tripositive lanthanide ion) for different molar nitrates concentrations c in the aqueous phase. The effect was referred to the covalency in Ln―O bonds, in products and substrates of the adsorption.
Keywords: Lanthanide; Tetrad effect; Adsorption; Zeolite;

Pullulan derivative was synthesized by coupling carboxymethylpullulan (degree of substitution DS 0 in = 0.7 ) and dimethylaminopropylamine (DMAPA), activated by a hydrosoluble carbodiimide N ′ -(3-dimethylaminopropyl)-N-ethylcarbodiimide hydrochloride (EDAC). FTIR and 13C and 1H NMR spectroscopic analyses have evidenced that the polysaccharide has been successfully modified. 1H NMR, nitrogen analysis, and conductimetric measurements allow determination of the degree of substitution in both carboxylic acid and amine functions. We have found that both functions present a similar DS of 0.35, which is characteristic of an ampholytic polymer with possible zwitterionic-type properties. Solution properties have been studied by flow field flow fractionation (F4) coupled on-line with multiangle laser light scattering (MALLS) and quasi elastic light scattering (QELS), surface tension, and viscosity measurements. The behavior has been found largely pH dependent and an amphiphilic behavior has been evidenced in alkaline media.Polyampholyte pullulan derivative (DMAP-CMP) was synthesized by coupling carboxymethylpullulan and dimethylaminopropylamine (DMAPA). As a result, the obtained derivative presents the same amount of carboxymethyl and amino functions (i.e., DS = 0.35 ). Solution properties have been found largely pH dependent and an amphiphilic behavior has been evidenced in alkaline media. Surface tension (equilibrated γ) versus pH for DMAP-CMP in pure water. C p = 2   g L −1 , T = 25 ° C .
Keywords: Ampholytic polymer; Amphiphilic; Polysaccharide; F4/MALLS;

Poly(N-isopropylacrylamide)/chitosan (PNIPAM/CS) core–shell microgel was synthesized by graft copolymerization. The microstructure of copolymers was characterized by FT-IR spectrum and 1H-nuclear magnetic resonance (1H NMR). Transmission electron microscope (TEM) and dynamic light scattering (DLS) measurements display that the microgel has high monodispersity and with a core–shell structure. For swelling the microgel in various alcohol solutions, the particles first shrink; then flocculation occurs resulted from weak aggregation of particles with the increase of alcohol concentration. The investigation of the size of microgels as a function of temperature shows that the thermo-sensitive property is markedly exhibited when the alcohol concentration is low, and vanishes when the alcohol concentration exceeds some value where the microgels have the lowest size.Poly(N-isopropylacrylamide)/chitosan (PNIPAM/CS) core–shell microgel was synthesized by graft copolymerization. The microstructure of copolymer was characterized by FT-IR spectrum and 1H-nuclear magnetic resonance (1H NMR). For swelling the microgel in various alcohol solutions, the particles first shrink and then flocculate when alcohol was increased to certain concentration. The investigation of the microgels size with temperature shows that the thermo-sensitive property is markedly exhibited when the alcohol concentration is lower, and vanishes while the alcohol concentration exceeds some value where the microgels have the lowest size.
Keywords: Core–shell microgel; Graft copolymerization; Thermosensitive property;

On the interface of a solid surface and a solution of nonadsorbing polymer there exists a depletion layer (DL), where the concentration of polymer segments is lower. Donath's electrophoretic theory, based on the decreased viscosity in the DL region, allows computing DL thickness from the relative (with and without polymer) electrophoretic mobility, the bulk viscosity, and the ionic strength. The aim of this work is to check experimentally Donath's nonlinear electrophoretic (NLE) theory under the most favorable conditions—liposomes in solutions of low-molecular poly(ethylene glycol) (PEG). In order to determine DL thickness, the dependence of mobility on viscosity is chosen instead on ionic strength. The value obtained from NLE theory is compared with the DL thickness calculated by Vincent's pragmatic theory. The conformation-statistical parameters are calculated on the base of viscosimetric measurements of PEG solution. The results indicate a few shortcomings of NLE theory. The main one is that DL thickness does not depend on polymer concentration, a fact that is in discrepancy with the prediction of Vincent's theory. The conclusion is that NLE theory describes well the experimental dependence of the relative mobility on the bulk viscosity, but it is inapplicable to quantitative determination of DL thickness.
Keywords: Nonadsorbing polymer; Polymer depletion; Depletion layer; Particle electrophoresis; Viscosity; Poly(ethylene glycol); Liposomes;

We report the fabrication of a Langmuir–Blodgett (LB) film of magnetic nanoparticles (iron oxide) coated by poly(N-alkylmethacrylamide)s with various alkyl chain lengths. The iron oxide nanoparticle (nP) was first modified with a reactive polymer, poly(N-hydroxysuccinimide methacrylate) (pSucMA) by applying surface initiated atom transfer radical polymerization (ATRP) technique. Then the succinimide group was replaced by various amine derivatives. The monolayer behaviors of the resultant nanoparticles, as modified by various poly(N-alkylmethacrylamide)s, such as poly(octylmethacrylamide) (pOMA), poly(dodecylmethacrylamide) (pDDMA), polytetradecylmethacrylamide (pTDMA), and poly(hexadecylmethacrylamide) (pHDMA) were elucidated using surface pressure–area isotherm measurements. Results show that pTDMA-modified nanoparticles (nP-pTDMA) exhibit the highest collapse pressure with a steeply rising surface pressure. The monolayer of nP-pTDMA on the water surface was transferred onto a solid substrate using the LB technique. Atomic force microscopy (AFM) images of the transferred LB film show that nP-pTDMA particles form a uniform nanoparticle monolayer. The LB film of nP-pTDMA with multilayers was fabricated through sequential transfer of the particles monolayer onto the substrate surface. The resultant LB film of nanoparticles shows a superparamagnetic behavior at room temperature.Magnetic particle covered with several poly(N-alkylmethacrylamide) was synthesized and the effect of the side chain length to monolayer properties of the nanoparticle was discussed.
Keywords: Magnetic nanoparticle; Langmuir–Blodgett film; Polymer shell;

Size-tuneable and micro-patterned iron nanoparticles derived from biomolecules via microcontact printing SAM-modified substrates and controlled-potential electrolyses by Masato Tominaga; Katsuya Miyahara; Kazuki Soejima; Shinya Nomura; Manabu Matsumoto; Isao Taniguchi (135-140).
Site-selected and size-controlled iron nanoparticles were prepared on coplanar surfaces via microcontact printing of SAM-modified Au/mica electrodes and controlled-potential electrolytic reactions using ferritin biomolecules. Ferritin molecules packed like a full monolayer on 6-amino-1-hexanethiol (AHT)- and 11-amino-1-undecanethiol (AUT)-modified Au/mica surface via electrostatic interactions, which did not depend on the chain length of the amino terminal alkane thiols. After heat-treatment at 400 °C for 60 min, iron oxide nanoparticles (ca. 5 nm in diameter) derived from ferritin cores were observed at the Au/mica surface by atomic force microscopy (AFM). On the study on the electrochemistry of ferritin immobilized onto AHT- and AUT-modified Au/mica electrodes, the redox response of the ferritin immobilized AHT-modified electrode was clearly observed. On the other hand, no redox peak for ferritin was obtained at the AUT-modified electrode. The electron transfer between ferritin and the electrode through the AUT membrane could not take place. The difference in the electrochemical response of ferritin immobilized onto AHT- and AUT-modified Au/mica was caused by the chain length of the amino terminal alkane thiols. Uniform patterns of AHT and AUT on the Au/mica electrode surface were performed by use of a poly(dimethylsiloxane) (PDMS) stamp. After the immobilization of ferritin onto both AHT- and AUT-modified electrode surfaces, the modified electrode was applied to a − 0.5  V potential for 30 min in a phosphate buffer solution. After this procedure, the PDMS stamp patterning image appeared by scanning electron microscopy (SEM) image. The SEM results induced by the size change of the ferritin core consisting of iron(III) by electrolysis.Site-selected and size-controlled iron nanoparticles can be prepared on a coplanar surface via PDMS stamping and controlled-potential electrolytic reaction using ferritin.
Keywords: Ferritin; Pattern; Nanoparticles; Iron oxide; Electrolysis;

Structural and shear characteristics of adsorbed sodium caseinate and monoglyceride mixed monolayers at the air–water interface by Juan M. Rodríguez Patino; Marta Cejudo Fernández; Cecilio Carrera Sánchez; Ma. Rosario Rodríguez Niño (141-151).
The structural and shear characteristics of mixed monolayers formed by an adsorbed Na-caseinate film and a spread monoglyceride (monopalmitin or monoolein) on the previously adsorbed protein film have been analyzed. Measurements of the surface pressure (π)–area (A) isotherm and surface shear viscosity ( η s ) were obtained at 20 °C and at pH 7 in a modified Wilhelmy-type film balance. The structural and shear characteristics of the mixed films depend on the surface pressure and on the composition of the mixed film. At surface pressures lower than the equilibrium surface pressure of Na-caseinate (at π < π e CS ), both Na-caseinate and monoglyceride coexist at the interface, with a structural polymorphism or a liquid expanded structure due to the presence of monopalmitin or monoolein in the mixture, respectively. At higher surface pressures, collapsed Na-caseinate residues may be displaced from the interface by monoglyceride molecules. For a Na-caseinate–monopalmitin mixed film the η s value varies greatly with the surface pressure (or surface density) of the mixed monolayer at the interface. In general, the greater the surface pressure, the greater are the values of η s . However, the values of η s for a Na-caseinate–monoolein mixed monolayer are very low and practically do not depend on the surface pressure. The collapsed Na-caseinate residues displaced from the interface by monoglyceride molecules at π > π e CS have important repercussions on the shear characteristics of the mixed films.Surface shear viscosity of (▪) spread caseinate and adsorbed (○, ●, ▵, ▴) caseinate, (◊) monopalmitin, (▿) monoolein and (▵) β-casein films.
Keywords: Food emulsifiers; Food dispersions; Protein–monoglyceride mixed films; Interfacial shear viscosity; Adsorbed films; Monolayer structure; Interfacial rheology; Air–water interface;

Stable cluster formation in aqueous suspensions of iron oxyhydroxide nanoparticles by Benjamin Gilbert; Guoping Lu; Christopher S. Kim (152-159).
Metal oxide and oxyhydroxide nanoparticles are important components of natural aqueous systems and have application in photocatalysis. Uncoated (oxyhydr)oxide nanoparticles can form charge-stabilized colloids in water, but the precise regimes of dispersion and aggregation have been determined for very few nanomaterials. We studied the colloidal behavior of ∼6 nm nanoparticles of iron oxyhydroxide (FeOOH), a common natural nanoscale colloid, and found that these nanoparticles formed stable suspended clusters under a range of aqueous conditions. Light and X-ray scattering methods show that suspended fractal nanoclusters are formed between pH 5 and 6.6 with well-defined maximum diameters that can be varied from 25 nm to approximately 1000 nm. The nanoclusters retain a very high surface area, and persist in suspension for at least 10 weeks in solution. The process is partially reversible because optically transparent suspensions are regained when nanoparticles that aggregated and settled at pH >7 are adjusted to pH 4 without stirring. However, completely redispersed nanoparticles are not obtained even after one month. Because nanocluster formation is controlled predominantly by surface charge, we anticipate that many metal oxide and other inorganic nanoparticles will exhibit equivalent cluster-forming behavior. Our results indicate that natural nanoparticles could form stable nanoclusters in groundwater that are likely to be highly mobile, with implications for the long-range transport of surface sorbed contaminants.
Keywords: Nanoparticles; Clusters; Aggregation; Colloid transport; Small-angle X-ray scattering; Dynamic light scattering; Photon correlation spectroscopy;

Avoiding “mud” cracks during drying of thin films from aqueous colloidal suspensions by E. Santanach Carreras; F. Chabert; D.E. Dunstan; G.V. Franks (160-168).
The critical cracking thickness of films obtained by drying aqueous alumina suspensions has been investigated. The effects of solution chemistry, binder and binder crosslinking were studied. Films formed from flocculated and dispersed suspensions are compared. The influence of the addition of the polymeric binder, poly(vinyl alcohol) (PVA) was also investigated. In addition, in some of the dispersed suspensions the PVA was covalently crosslinked. The critical cracking thickness is found to be 3 times greater for the films obtained from dispersed suspensions than for the films obtained from flocculated suspensions. The superior mechanical properties are primarily due to the higher final solids concentration in the films obtained from dispersed suspensions. Addition of PVA leads to an increase of the critical cracking thickness by a factor of two for both dispersed and flocculated systems. When the PVA is crosslinked, the mechanical properties of the gel during drying are improved and the critical cracking thickness is increased 10 fold with respect to the suspensions with uncrosslinked PVA.The critical cracking thickness h c of dried films is improved by controlling the aqueous alumina suspension formulation. On the left is a 430-μm thick cracked film of pH 9 suspension where h ≈ 3 h c . On the right is a 1265-μm thick cracked film of pH 1.75 suspension where h ≈ 3 h c .
Keywords: Thin film; Cracking; Drying; Suspension; Alumina; PVA; Crosslinking;

Effects of the anionic surfactants, sodium dodecyl sulfate and sodium oleate, on the formation and properties of silica colloidal nanoparticles were investigated. At a concentration of ∼ 1 × 10 −3  M , adsorption of anionic surfactants increased particle size, monodispersity, and negative surface charge density of synthesized silica particles. As uniformity of particle size and particle–particle interactions increase, colloidal photonic crystals readily self-assemble without extensive washing of the synthesized silica nanoparticles. The photonic crystals diffract light in the visible region according to Bragg's law. The assembled colloidal particle arrays exhibit a face-centered cubic structure in dried thin films. This study offers a new approach for producing ordered colloidal silica thin films.
Keywords: Silica; Surfactant; Colloids; Nanoparticles; Photonic crystals; Self-assembly; Thin film;

Hydroxyl functionalized thermosensitive microgels with quadratic crosslinking density distribution by Begum Elmas; Murvet Tuncel; Serap Şenel; S. Patir; Ali Tuncel (174-183).
N-isopropylacrylamide (NIPA) based uniform thermosensitive microgels were synthesized by dispersion polymerization by using relatively hydrophilic crosslinking agents with hydroxyl functionality. Glycerol dimethacrylate (GDMA), pentaerythritol triacrylate (PETA) and pentaerythritol propoxylate triacrylate (PEPTA) were used as crosslinking agents with different hydrophilicities. A protocol was first proposed to determine the crosslinking density distribution in the thermosensitive microgel particles by confocal laser scanning microscopy (CLSM). The microgels were fluorescently labeled by using hydroxyl group of the crosslinking agent. The CLSM observations performed with the microgels synthesized by three different crosslinking agents showed that the crosslinking density exhibited a quadratic decrease with the increasing radial distance in the spherical microgel particles. This structure led to the formation of more loose gel structure on the particle surface with respect to the center. Then the use of hydrophilic crosslinking agents in the dispersion polymerization of NIPA made possible the synthesis of thermosensitive microgels carrying long, flexible and chemically derivatizable (i.e., hydroxyl functionalized) fringes on the surface by a single-stage dispersion polymerization. The microgels with all crosslinking agents exhibited volume phase transition with the increasing temperature. The microgel obtained by the most hydrophilic crosslinking agent, GDMA exhibited higher hydrodynamic diameters in the fully swollen form at low temperatures than those obtained by PETA and PEPTA. Higher hydrodynamic size decrease from fully swollen form to the fully shrunken form was also observed with the same microgel. N-isopropylacrylamide based uniform thermosensitive microgels were synthesized by dispersion polymerization by using relatively hydrophilic crosslinking agents with hydroxyl functionality, glycerol dimethacrylate, pentaerythritol triacrylate and pentaerythritol propoxylate triacrylate. A protocol was proposed to determine the crosslinking density distribution in the thermosensitive microgel particles by confocal laser scanning microscopy (CLSM).
Keywords: Thermosensitive polymer; N-isopropylacrylamide; Dispersion polymerization; Latex; Microgels; Pentaerythritol; Glycerol dimethacrylate; Confocal laser scanning microscopy;

The calcite/water interface by Rasmus Eriksson; Juha Merta; Jarl B. Rosenholm (184-193).
Suspensions of calcium carbonate in water with an indifferent background electrolyte (NaCl) have been investigated using several techniques. Particular attention was paid to the dissolution of calcite at equilibrium and as a function of sodium polyacrylate (NaPA) concentration. Also of interest was how this affects the magnitude of the surface charge and the zeta potential. The development of the interfacial charge is discussed with respect to the dissolved species and with regard to the kinetics of dissolution. The partial pressure of CO2 in solution is believed to play a major role in determining the sign of the charge at equilibrium. In addition to effectively stabilizing calcite suspensions, NaPA was also found to act as a chelating agent at the calcite surface, enhancing the dissolution. The order of addition of NaPA to the suspensions was found to be important.The background calcium ion concentration resulting from the dissolution of calcite is a major factor in determining the effectiveness of NaPA as a suspension stabilizer.
Keywords: Calcium carbonate; Sodium polyacrylate; Dissolution; Electrostatic stabilization; Surface charge; Zeta potential;

Influence of aqueous aging on surface properties of plasma sprayed oxide coatings by Mika Harju; Johanna Halme; Mikael Järn; Jarl B. Rosenholm; Tapio Mäntylä (194-201).
The influence of aging in mild aqueous conditions (pH 4, 7 and 9) on surface properties of plasma sprayed oxide was studied using electrophoretic mobility studies and measuring concentrations of dissolved species from exposure liquids. In addition, required acid/base additions to maintain constant pH, redox potentials suspension conductivities were measured. The experiment time was two weeks. The plasma sprayed materials were based on Al2O3, TiO2 and Cr2O3. Materials based on Al2O3 dissolved easily at pH 4 due to presence of metastable γ-Al2O3 phase. In addition there was clear change in surface charging properties (zeta potential) of Al2O3 surfaces so that the estimated IEP value drifted from >9 at the beginning of aging and dropped down to 8.5–8.7 after 2 weeks of treatment. Plasma sprayed TiO2 did not dissolve under the experiment conditions. Even thought the surface charging (zeta potential) changed during the exposure, the estimated IEP remained close to the values reported for pure TiO2 materials. Plasma sprayed Cr2O3 based materials were also insoluble at the studied pH values. On the other hand, the estimated IEP values deviated radically from the reported PZC values of similar materials.The influence of aqueous aging treatment on surface properties of plasma sprayed Al2O3, TiO2 and Cr2O3 coating materials was evaluated.
Keywords: Plasma spraying; Zeta-potential; Isoelectric point; IEP; Alumina; Titania; Chromia;

The electrokinetic potentials of anatase (titanium dioxide) and α-alumina were studied by means of various instruments in the presence of sodium and potassium trichloroacetates, trifluoroacetates, and trifluoromethanesulfonates at various pH, ionic strengths, and solid-to-liquid ratios. At concentrations up to 0.01 M, these salts do not induce substantial shifts in the isoelectric point of the oxides. Such behavior is typical of inert electrolytes.The zeta potential of anatase (titanium dioxide) in 0.001 M solutions of 1–1 salts as measured by means of electrophoresis. The electroacoustic method produced similar results.
Keywords: ζ potential; Point of zero charge; Isoelectric point; Indifferent electrolyte; Specific adsorption;

Study on reaction kinetics of synthesis of thioether by a visualization technique by Jin-Fang Chen; Fang-Feng Hu; Jun-Hui Xu; Qi-Ming Chen; Zhong Chen; Jia Guo (207-212).
In this paper, a novel technique combined light-electronic microscopy and computer imaging trace was used to investigate the synthesis of thioether, which is an intermediate for lansoprazole. The reaction kinetics study by a visualization technique was carried out in a minireactor, and the concentration–grayscale standard curves for thioether were obtained by analyzing the grayscales of digital images for the solutions with 20 different concentrations. Based on the concentration–grayscale standard curves, the reactant concentrations at different times were calculated and the reaction kinetic curve as well as the reaction rate equation were obtained. It was found that the total mass-transfer resistance of sodium imidazole was larger than that of bromopyridine. Liquid–liquid interface of synthesizing thioether was observed and its mass transfer mechanism was discussed.The thickness of tiny droplets near the interface changed with the time elapsed. Fig. 1 displayed the interface of dichloromethane–water at the moment of 120 min.
Keywords: Visualization; Thioether synthesis; Concentration–grayscale standard curve; Reaction kinetic; Liquid–liquid interface;

The submicrometer-sized titania hollow spheres have been synthesized by employing sulfonated polystyrene latex particles as a template in sol–gel method. Photocatalytic activity of the hollow spheres was investigated by focusing on the effect of electron scavengers in the photocatalytic decomposition of methylene blue (MB). Photocatalytic activities of titania hollow spheres were significantly enhanced by the addition of peroxydisulfate as an electron scavenger. The rate constant for photodecomposition of MB was increased more than two times by the addition of peroxydisulfate. The significant increase in the photodecomposition rate seems to be related to electrons scavenging as well as production of additional oxidizing species. It was found that the optimum concentration of peroxydisulfate was 10 mM. Further increase in the concentration of peroxydisulfate is not recommended due to the saturation of reaction rate by the excess amount of SO 4 2 − species.Submicrometer-sized titania hollow spheres have been synthesized by employing sulfonated polystyrene latex particles as a template in sol–gel method. Photocatalytic activity of the hollow spheres was investigated by focusing on the effect of peroxydisulfate electron scavengers in the photocatalytic decomposition of methylene blue (MB).
Keywords: Titania hollow spheres; Sol–gel method; Photocatalytic activity; Electron scavenger; Methylene blue; Peroxydisulphate;

Study on the NaNp/CpTiCl3/Al2O3–SiO2 system by Paweł Maksimowski; Wincenty Skupiński (219-231).
CpTiCl3/Al2O3–SiO2/NaNp (Cp = cyclopentadienyl, Np = naphthenide anion) system was obtained by a reduction of cyclopentadienyl titanium[IV] complexes supported on alumina-silica gels with sodium naphthenide in dinitrogen or argon atmospheres. The yield of the reduction reactions and the yield of dinitrogen fixation by the systems reduced in dinitrogen depend on the kind of phases which are present on alumina-silica gel surfaces according to their composition. On hydrolysis the nitrogen titanium complexes obtained liberated ammonia. The highest yields of these reactions, above 70% calculated as NH3/Ti ratio, were obtained for the systems containing in the carriers 10-, 60-wt%, of Al2O3 and SiO2Deg of aerosil type. This relatively high activity was achieved with surface titanium complexes obtained by a reaction of CpTiCl3 with isolated surface hydroxyl groups of neutral properties present on these gels. The EPR method was used to investigate the titanium[III] complexes formed during reduction of the systems. The signals obtained helped in discussion concerning the way in which titanium complexes undergo transformations during the reactions studied.
Keywords: Alumina-silica; Supported half sandwich titanocene; Nitrogen fixation; EPR;

A catalytic effect is found for methanol oxidation after new active surface states are produced on polycrystalline platinum by potentiostatic cathodization in acid media at room temperature. This procedure originates surface states not available on the original polycrystalline electrodes with unexpected cyclic voltammetric responses; i.e., at least four new peaks below 0.9 V are observed. The cathodization process also induces a rearrangement of the bulk platinum oxide, showing a defined peak at 1.2 V. The appearance of these new states is also proven by open-circuit potential decays. The electrocatalytic activity of these new surfaces in methanol oxidation is compared with that of the untreated electrodes by electrochemical impedance spectroscopy, chronoamperometry, and cyclic voltammetry. The cathodic procedure enhances the methanol oxidation voltammetric current peaks with charge density values higher than those on untreated platinum. The integration of chronoamperometric plots over 10 min in methanol acid media presents the largest difference between 0.6 and 0.7 V with respect to the original surface. Analysis of the impedance data shows that the values of polarization resistance for methanol oxidation on the cathodically treated platinum are lower than those of the original surface. According to the time constant values for methanol oxidation, the original surface can be considered less tolerant of the formation of catalytic poisons. A discussion of the most likely mechanism for the formation of the new active sites on platinum is presented here, assuming the presence of hydrogen subsurface states, ordered water clusters, and low-coordinated platinum atoms.New superactive states on platinum can be produced by potentiostatic cathodization in acid media, which are not available on original platinum. They are characterized by the appearance of the occluded hydrogen species, which later form hydroxyl subsurface states. The following scheme explains the effect.
Keywords: Electrocatalysis; Platinum; Methanol; Subsurface hydrogen; Ordered water;

Electrochemical methods for pollution abatement have been shown to be viable alternatives or complementary to biological treatment in some instances, especially when pollutants are recalcitrant to biological processing. Electrochemical oxidation and reduction have been found successful in decomposing the most resilient compounds, and electrolysis is assigned an important role in the elucidation of the electrode process. Small well-defined cathodic and anodic peak were observed that on controlled-potential electrolysis (CPE) reduced substantially with a considerable decrease in color and absorbance. The rate of decrease of the current and absorbance was found to exhibit a first-order dependence. The COD of the solutions showed a decrease from 1416 to 352 mg/L. No peak could be observed in the voltammograms after CPE, indicating the absence of any electroactive substance left in the solutions. Results show that electrochemical reduction is a superior technology for treatment of dyes, as there is no simultaneous addition of anions, such as sulfate or chloride.Structure of Reactofix Golden Yellow 3 RFN.
Keywords: Electrochemical methods; Electrode; Reactofix Golden Yellow 3 RFN; COD;

Cathodic adsorptive stripping voltammetric studies on lamivudine: An antiretroviral drug by Rajeev Jain; Nimisha Jadon; Keisham Radhapyari (254-260).
The electrochemical reduction and adsorption of lamivudine, a systemic antiviral drug, were studied in a phosphate buffer medium at a hanging mercury drop electrode (HMDE). Cyclic voltammetry studies showed one well-defined reduction peak in the potential range from −1.2 to − 1.8   V under different pH conditions, but the best results were obtained at pH 3.4. The reduction was irreversible and exhibited diffusion-controlled adsorption. The response was evaluated with respect to preconcentration time, pH effect, accumulation potential, accumulation time, and scan rate. The number of electrons transferred in the reduction process was calculated and the probable reduction mechanism was proposed. A systemic study of the experimental parameters that affect the square-wave stripping response was carried out and experimental conditions were optimized.The electrochemical reduction and adsorption of lamivudine, a systemic antiviral drug, were studied in phosphate buffer medium at a hanging mercury drop electrode (HMDE). The response was evaluated with respect to preconcentration time, pH effect, accumulation potential, accumulation time, and scan rate.
Keywords: Lamivudine; Cathodic adsorptive stripping voltammetry; HMDE; Cyclic voltammetry; Pharmaceutical formulations;

The N-terminal His-tag affects the enantioselectivity of staphylococcal lipases: A monolayer study by Adel Sayari; Habib Mosbah; Robert Verger; Youssef Gargouri (261-267).
In order to check the influence of the polyhistidine tag at the N-terminus of recombinant lipases, a comparative study on the interfacial properties of native and recombinant Staphylococcus simulans (SSL and rSSL) or Staphylococcus xylosus lipase (SXL and rSXL) was investigated using the monomolecular film technique. No phospholipase activity was detected with rSSL or rSXL when using different phospholipids spread as monomolecular films maintained at various surface pressures, suggesting that the His-tag in the N-terminus of the recombinant proteins, do not affect the substrate recognition. The critical surface pressure measured with monomolecular films of egg-PC was slightly lowered with the two recombinant proteins compared to the native SSL or SXL one. A kinetic study on the surface pressure dependency, stereoselectivity and regioselectivity of native and recombinant SSL or SXL was performed using three dicaprin isomers spread as monomolecular films at the air–water interface. Our results show clearly that the presence of polyhistidine tag at the N-terminus of SSL or SXL changes their stereo- and regioselectivity.The N-terminal His-tag affects critically the regio- and the stereoselectivity of two recombinant staphylococcal lipases (Staphylococcus simulans lipase and Staphylococcus xylosus lipase).
Keywords: Staphylococcus simulans lipase; Staphylococcus xylosus lipase; His-tagged lipases; Monomolecular films; Critical surface pressure; Stereoselectivity; Regioselectivity;

Grafting of montmorillonite with different functional silanes via two different reaction systems by Wei Shen; Hongping He; Jianxi Zhu; Peng Yuan; Ray L. Frost (268-273).
Silane grafted montmorillonites were synthesized by using 3-aminopropyltriethoxysilane and trimethylchlorosilane via two different grafting reaction systems: (a) ethanol–water mixture and (b) vapor of silane. The resulting products were investigated using Fourier transform infrared (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA). XRD patterns demonstrate that silane was intercalated into the montmorillonite gallery, as indicated by the increase of the basal spacing. The product prepared by vapor deposition has a larger basal spacing than that obtained from solution, due to the different extent of silane hydrolysis in various grafting systems. TGA curves indicate that the methyl groups penetrate into the siloxane clay are the primary reason for the decrease of the dehydroxylation temperature of the grafted products. 3-Aminopropyltriethoxysilane in the grafted montmorillonite adopts a bilayer arrangement while trimethylchlorosilane adopts a monolayer arrangement within the clay gallery.The intensities of stretching vibrations of ―CH2 in γ-APS show that product prepared in silane vapor (M-APS-2) have more silane loading than that synthesized in ethanol–water mixture (M-APS-1). This proposal is further evidenced by TG and XRD results.
Keywords: Montmorillonite; Grafting; 3-Aminopropyltriethoxysilane; Trimethylchlorosilane; Fourier transform infrared; X-ray diffraction; Thermogravimetric analysis;

Dynamic wetting of Boger fluids by Y. Wei; G.K. Seevaratnam; S. Garoff; E. Ramé; L.M. Walker (274-280).
The impact of fluid elasticity on the dynamic wetting of polymer solutions is important because many polymer solutions in technological use exhibit non-Newtonian behaviors in the high shear environment of the wedge-like flow near a moving contact line. Our former study [G.K. Seevaratnam, Y. Suo, E. Ramé, L.M. Walker, Phys. Fluids 19 (2007) Art. No. 012103] showed that shear thinning induced by a semi-flexible high molecular weight polymer reduces the viscous bending near a moving contact line as compared to a Newtonian fluid having the same zero-shear viscosity. This results in a dramatic reduction of the dependence of the effective dynamic contact angle on contact line speed. In this paper, we discuss dynamic wetting of Boger fluids which exhibit elasticity-dominated rheology with minimal shear thinning. These fluids are prepared by dissolving a dilute concentration of high molecular weight polymer in a “solvent” of the oligomer of the polymer. We demonstrate that elasticity in these fluids increases curvature near the contact line but that the enhancement arises mostly from the weakly non-Newtonian behavior already present in the oligomeric solvent. We present evidence of instabilities on the liquid/vapor interface near the moving contact line.We investigate the impact of fluid elasticity on dynamic wetting by measuring the shape of a fluid meniscus on a solid being forced into a fluid bath at constant speed.
Keywords: Wetting; Contact angle; Boger fluid; Elastic fluid; Non-Newtonian; Polymer solution;

Structural ordering of organovermiculite: Experiments and modeling by Gražyna Simha Martynková; Marta Valášková; Pavla Čapková; Vlastimil Matějka (281-287).
The ordering of three different sizes of quaternary ammonium salts (QUATs) has been studied with respect to concentration of guests in the host's interlayer gallery. From the modeling, we could verify that small molecules of n-butylammonium salt build a monolayer structure in the vermiculite gallery without reference to concentration. On the other hand, the larger molecules of dodecyltrimethylammonium and dioctadecyldimethylammonium salts are responsive to the numbers of their molecules in the interlayer space of the host, building mono- or bilayered structures. Supersaturated structure of both QUATs keep an arrangement of alkyl chains nearly perpendicular to silicate layers, while only saturated samples exhibit tilted alkyl chains in the gallery. The ordering changes bring out the calculation of mean crystallite size. Low values of the nonbond energy of supersaturated forms predict that those organovermiculites will readily exfoliate, e.g., in polymer/clay nanocompositeThe ordering of organovermiculites depends on the type of molecules in vermiculite interlayer space. The supersaturated form can utilize the best of the organophilic properties.
Keywords: Quaternary ammonium salts; Vermiculite; Intercalation; Modeling; Nonbond energy; Mean crystallite size; XRD;

Understanding micelle formation requires its complete thermodynamic characterization. In this work micellization of the model ionic surfactants decyltrimethylammonium chloride (DETAC), dodecyltrimethylammonium chloride (DTAC) and tetradecyltrimethylammonium chloride (TTAC) was investigated by high performance conductivity measurements, using instrumentation developed in our laboratory. The temperature dependence of the critical micelle concentration exhibits a minimum characterized by Δ mic H 0 = 0 (endothermic to exothermic process) and the degree of micelle ionization increases slightly with increasing temperature. The temperature change of Δ mic S 0 indicates that the process of micellization is entropically driven. Δ mic G 0 is always negative and slightly temperature dependent. The temperature dependence of the thermodynamic parameters is discussed in terms of the alkyl chain length and nature of the counterion. The micellization process is more favourable for surfactants with longer alkyl chain length and larger (less hydrated) counterions.
Keywords: Electric conductivity; Thermodynamics of micelle formation; Trimethylammonium chloride; Micellization;

Synthesis and micellar properties of surface-active ionic liquids: 1-Alkyl-3-methylimidazolium chlorides by Omar A. El Seoud; Paulo Augusto R. Pires; Thanaa Abdel-Moghny; Erick L. Bastos (296-304).
A series of surface-active ionic liquids, RMeImCl, has been synthesized by the reaction of purified 1-methylimidazole and 1-chloroalkanes, RCl, R = C 10 , C 12 , C 14 , and C16, respectively. Adsorption and aggregation of these surfactants in water have been studied by surface tension measurement. Additionally, solution conductivity, electromotive force, fluorescence quenching of micelle-solubilized pyrene, and static light scattering have been employed to investigate micelle formation. The following changes resulted from an increase in the length of R: an increase of micelle aggregation number; a decrease of: minimum area/surfactant molecule at solution/air interface; critical micelle concentration, and degree of counter-ion dissociation. Theoretically-calculated aggregation numbers and those based on quenching of pyrene are in good agreement. Gibbs free energies of adsorption at solution/air interface, Δ G ads 0 , and micelle formation in water, Δ G mic 0 , were calculated, and compared to those of three surfactant series, alkylpyridinium chlorides, RPyCl, alkylbenzyldimethylammonium chlorides, RBzMe2Cl, and benzyl(3-acylaminoethyl)dimethylammonium chlorides, R ′ AEtBzMe 2 Cl , respectively. Contributions to the above-mentioned Gibbs free energies from surfactant methylene groups (in the hydrophobic tail) and the head-group were calculated. For RMeImCl, the former energy is similar to that of other cationic surfactants. The corresponding free energy contribution of the head-group to Δ G mic 0 showed the following order: RPyCl ≈ RBzMe 2 Cl > RMeImCl > R ′ AEtBzMe 2 Cl . The head-groups of the first two surfactant series are more hydrophobic than the imidazolium ring of RMeImCl, this should favor their aggregation. Micellization of RMeImCl, however, is driven by a relatively strong hydrogen-bonding between the chloride ion and the hydrogens in the imidazolium ring, in particular the relatively acidic H2. This interaction more than compensates for the relative hydrophilic character of the diazolium ring. As indicated by the corresponding Δ G mic 0 , micellization of R ′ AEtBzMe 2 Cl is more favorable than that of RMeImCl because the ―CONH― group of the former surfactant series forms hydrogen bonds to both the counter-ion and the neighboring molecules in the micelle.
Keywords: Ionic liquids; Ionic liquids; Imidazole-based cationic surfactants; Surface tension; Conductance; ISE; Fluorescence;

The rheological properties of aqueous suspensions consisting of cationic starch (CS) and positively charged aluminum magnesium hydrotalcite-like compound (HTlc) were investigated. Special emphasis was placed on the thixotropic phenomena. With the increase of mass ratio (R) of HTlc to CS, the equilibrium viscosity ( η eq ) and the consistency coefficient (m) values of the suspensions increase in the range of neutral and alkaline pH (higher than 6.5) while decrease in the range of acid pH (lower than 6.5). With the increase of pH value, the η eq and m values of the suspensions in the R range of 0–0.08 studied increase initially and then decrease, appearing a maximum value at about pH 7.41 ± 0.25 . The CS/HTlc suspensions display viscid character and the yield point of the suspensions was not observed except the suspension with R = 0.08 in the pH range of 7.66–9.70, which showed a yield point and viscoelasticity. The CS/HTlc suspensions may display different thixotropic types: negative, complex or positive thixotropy, depending on pH and R value. The thixotropic type of the CS/HTlc suspension may be transformed from negative (pure CS solution), through complex ( R = 0.02 ), into positive thixotropy ( R = 0.05 and 0.08) with the increase of R in the studied R range of 0–0.08, and the thixotropic strength of the suspensions increases initially and then decreases with pH value in the pH range studied. The mechanism of the thixotropic phenomenon is discussed.Rheological properties of aqueous suspensions containing cationic starch (CS) and hydrotalcite-like compound (HTlc) were investigated. Special emphasis was placed on the thixotropic phenomena.
Keywords: Rheology; Thixotropy; Suspension; Cationic starch; Hydrotalcite-like compounds;

Electrokinetic coupling in unsaturated porous media by A. Revil; N. Linde; A. Cerepi; D. Jougnot; S. Matthäi; S. Finsterle (315-327).
We consider a charged porous material that is saturated by two fluid phases that are immiscible and continuous on the scale of a representative elementary volume. The wetting phase for the grains is water and the nonwetting phase is assumed to be an electrically insulating viscous fluid. We use a volume-averaging approach to derive the linear constitutive equations for the electrical current density as well as the seepage velocities of the wetting and nonwetting phases on the scale of a representative elementary volume. These macroscopic constitutive equations are obtained by volume-averaging Ampère's law together with the Nernst–Planck equation and the Stokes equations. The material properties entering the macroscopic constitutive equations are explicitly described as functions of the saturation of the water phase, the electrical formation factor, and parameters that describe the capillary pressure function, the relative permeability functions, and the variation of electrical conductivity with saturation. New equations are derived for the streaming potential and electro-osmosis coupling coefficients. A primary drainage and imbibition experiment is simulated numerically to demonstrate that the relative streaming potential coupling coefficient depends not only on the water saturation, but also on the material properties of the sample, as well as the saturation history. We also compare the predicted streaming potential coupling coefficients with experimental data from four dolomite core samples. Measurements on these samples include electrical conductivity, capillary pressure, the streaming potential coupling coefficient at various levels of saturation, and the permeability at saturation of the rock samples. We found very good agreement between these experimental data and the model predictions.Resistivity, capillary pressure curve, and relative streaming potential coupling coefficient versus saturation of water in a porous medium.
Keywords: Electro-osmosis; Streaming potential; Stokes equation; Nernst–Planck equation; Porous media; Clay; Saturation; Capillary pressure;

The effective medium model [H.C. Brinkman, Appl. Sci. Res. A 1 (1947) 27] is used to calculate the electrophoretic mobility of spheres in a gel with uniform zeta potential on their surface. In the absence of a gel support medium or ion relaxation (the distortion of the ion atmosphere from equilibrium due to the presence of an external flow or electric field), our results reduce to those of Henry [D.C. Henry, Proc. R. Soc. London Ser. A 133 (1931) 106]. The relaxation effect can be ignored for weakly charged particles, or for particles with low absolute zeta potential. Using a procedure similar to that employed by O'Brien and White [R.W. O'Brien, L.R. White, J. Chem. Soc. Faraday Trans. 2 74 (1978) 1607], the relaxation effect is accounted for in the present work and results are presented over a wide range of particle sizes, gel concentrations, and zeta potentials in KCl salt solutions. In the limit of no gel, our results reduce to those of earlier investigations. The procedure is then applied to the mobility of Au nanoparticles in agarose gels and model results are compared to recent experiments [D. Zanchet, C.M. Micheel, W.J. Parak, D. Gerion, S.C. Williams, A.P. Alivisatos, J. Phys. Chem. B 106 (2002) 11758; T. Pons, H.T. Uyeda, I.L. Medintz, H. Mattoussi, J. Phys. Chem. B 110 (2006) 20308]. Good agreement with experiment is found for reasonable choices of the model input parameters.Reduced mobility, ξ, over reduced zeta potential, Y, versus κ a for a sphere in different gel environments. Ion relaxation is included (salt is KCl) and Y = 5 . From the uppermost to lowermost lines, λ / κ = 0.0 (open squares and solid line), 0.010 (filled squares and dashed line), 0.027 (open diamonds and dotted line), 0.072 (filled diamonds and solid line), 0.193 (open triangles and dashed line), 0.519 (filled triangles and dotted line), 1.389 (×s and solid line), 3.727 (∗s and dashed line), 10.0 (+s and dotted line).
Keywords: Gel electrophoresis of spheres; Nanoparticle gel electrophoresis; Transport in gels; Effective medium modeling of electrophoresis;

Monodispersed hollow ZnS microspheres have been successfully synthesized by a facile ethylenediamine tetraacetic acid (EDTA) mediated hydrothermal route. The sizes of the hollow spheres vary from 1.5 to 3.5 μm when the reaction temperature varied from 130 to 230 °C. The formation of these hollow spheres is attributed to the oriented aggregation of ZnS nanocrystals around the gas–liquid interface between H2S and water. EDTA plays important role as chelating ligand and capping reagent, which regulates the release of Zn2+ ions for the formation of ZnS hollow spheres. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–vis spectroscopy, photoluminescence, and Raman spectroscopy. The obtained ZnS hollow spheres show a sharp and photostable UV emission ∼370 nm, which is attributed to the recombination process associated with interstitial sulfur vacancy.Well crystalline ZnS hollow spheres with diameters ranging from 1.5 to 3.5 μm and shell thickness from 230 to 700 nm showing ultraviolet emission have been successfully synthesized through a novel one-step hydrothermal process using EDTA as the complexing agent. A suitable mechanism for the formation of ZnS hollow spheres is discussed.
Keywords: ZnS; Hollow sphere; Hydrothermal process; Photoluminescence;

We describe predictions of properties of copolymer-stabilized nanoparticles in the presence of an oil–water interface based on Brownian dynamics simulations. These simulations provide information regarding the equilibrium and diffusion properties of the stabilized particles. The hydrophilic part of the copolymer is modeled as a polyelectrolyte and is described at the Debye–Hückel level. Both block and random copolymers are considered. The surface area of particles at the fluid interface and the diffusion properties of the particles give some guidance into the copolymer architectures that may be most useful for stabilizing nanoparticles at fluid interfaces. We find based on our results that a conservative recommendation to enhance transportability in a water phase and attachment to an oil–water interface would be to design nanoparticles with a random copolymer attached to them.Brownian dynamics simulations are used to examine segregation of copolymer-stabilized nanoparticles to oil–water interfaces.
Keywords: Nanoparticles; Brownian dynamics; Oil–water interfaces;

Growth of highly oriented crystalline polyaniline films by self-organization by D.S. Sutar; N. Padma; D.K. Aswal; S.K. Deshpande; S.K. Gupta; J.V. Yakhmi (353-358).
Silicon substrates with (100) orientation were modified with amino-silane self-assembled monolayer (SAM) to provide amino (NH2) moieties at the substrate surface. Self-organization of polyaniline during chemical polymerization, on this modified surface, leads to the growth of highly oriented films at the substrate–polymer interface. The morphology studied using scanning electron microscopy and atomic force microscopy revealed the formation of polymer film with well faceted pyramidal crystallites. XPS and FTIR spectroscopy were used to analyze the chemical structure of the film. X-ray diffraction measurements show the crystalline nature of the polyaniline, whose lattice parameters are in agreement with the reported values. This study underlines the importance of a SAM in deciding the structure and morphology of the deposited polymer.Amino-silane self-assembled monolayer was used to modify the surface of (100) oriented silicon substrate and provide amino (NH2) groups at the surface. On this substrate surface, self-organization of polyaniline during chemical polymerization, yields highly oriented crystalline polyaniline film with oriented pyramid-shaped crystallites.
Keywords: Polyaniline; Self-assembly; SAM; Thin films; Morphology; Structure; Crystallinity;

Adsorption behaviors of high-valence metal ions on desferrioxamine B immobilization nylon 6,6 chelate fiber under highly acidic conditions by Yoshitaka Takagai; Atsushi Takahashi; Hitoshi Yamaguchi; Toshio Kubota; Shukuro Igarashi (359-362).
Adsorption behaviors of the high-valence metal ions Zr(IV), Hf(IV), Ti(IV), V(V), Nb(V), Ta(V), and Mo(IV) on desferrioxamine B (DFB) immobilization nylon 6,6 chelate fiber was investigated under highly acidic conditions. Though the complexes of DFB and the high-valence metal ions were extracted without selectivity by solvent extraction, the only zirconium ions showed higher adsorption percentages than that of other high-valence metal ions on the DFB immobilization nylon 6,6 chelate fiber. Adsorption properties were caused that limited the freedom of DFB by chemical immobilization. Especially, hafnium ions and zirconium ions, which have similar chemical properties, showed different adsorption behavior in highly acidic aqueous solutions. Zirconium ions were quantitatively adsorbed up to 13.5 μmol/g.
Keywords: Desferrioxamine B; High-valence metal ions; Zirconium; Nylon 6,6; Chelate fiber; Hafnium ions; Adsorption;

Interaction of lipophilic gemcitabine prodrugs with biomembrane models studied by Langmuir–Blodgett technique by Francesco Castelli; Maria Grazia Sarpietro; Flavio Rocco; Maurizio Ceruti; Luigi Cattel (363-368).
The stability and bioavailability of anticancer agents, such as gemcitabine, can be increased by forming prodrugs. Gemcitabine is rapidly deaminated to the inactive metabolite ( 2 ′ , 2 ′ -difluorodeoxyuridine), thus to improve its stability a series of increasingly lipophilic gemcitabine prodrugs linked through the 4-amino group to valeroyl, lauroyl, and stearoyl acyl chains were synthesized. Studies of monolayer properties are important to improve understanding of biological phenomena involving lipid/gemcitabine or lipid/gemcitabine derivative interactions. The interfacial behavior of monolayers constituted by DMPC plus gemcitabine or lipophilic gemcitabine prodrugs at increasing molar fractions was studied at the air/water interface at temperatures below (10 °C) and above (37 °C) the lipid phase transition. The effect of the hydrophobic chain length of gemcitabine derivatives on the isotherm of pure DMPC was investigated by surface tension measurement, and the results are reported as molar fractions as a function of mean molecular area per molecule. The results show that the compounds interact with DMPC producing mixed monolayers that are subject to an expansion effect, depending on the prodrug chain length. The results give useful hints of the interaction of these prodrugs with biological membranes and increase knowledge on the incorporation site of such compounds, as a function of their lipophilicity, in a lipid carrier; they may lead to improved liposomal formulation design.The interaction of gemcitabine and lipophilic gemcitabine prodrugs with biomembrane models was investigated revealing the importance of the lipophilic moiety length on such interaction.
Keywords: Gemcitabine; Lipophilic gemcitabine derivatives; Dimyristoylphosphatidylcholine; Langmuir–Blodgett;

Macroporous solids with crystalline layered walls were fabricated from colloidal mixtures of size-controlled niobate nanosheets and polystyrene spheres. The macroporous solids, obtained after burning off the spheres, were characterized by scanning electron microscopy and X-ray diffraction. The obtained structures strongly depended on the lateral dimension L of the nanosheets used. When small nanosheets ( L = 100   nm ) were used, partly ordered macroporous solids with interconnected pores were obtained, whereas sponge-like random macroporous structures were obtained with larger nanosheets ( L = 190 and 270 nm). Peapod-like hollow structures were obtained when we used small ( L = 190   nm ) and very large ( L = 3   μm ) nanosheets at the same time. The microstructure of the pore walls was controllable by changing the calcination conditions. The walls were composed of propylammonium/K4Nb6O17 intercalation compound which has a layered structure with exchangeable cations in the interlayer space, stable up to 350 °C for 6 h on calcination. The walls were converted to crystalline K8Nb18O49 after calcination at 500 °C for 6 h.Sponge-like and peapod-like macroporous solids with crystalline layered walls were fabricated from colloidal mixtures of size-controlled niobate nanosheets and polystyrene spheres.
Keywords: Inorganic nanosheet; Macroporous solid; Ion-exchangeable layered niobate;

Surface tension of pure and water-containing ionic liquid C5MIBF4 (1-methyl-3-pentylimidazolium tetrafluoroborate) by Jia-Zhen Yang; Jing Tong; Jing-Bin Li; Ji-Guan Li; Jian Tong (374-377).
The surface tension of ionic liquid (IL) C5MIBF4 (1-methyl-3-pentylimidazolium tetrafluoroborate) with various amount of water was measured by the forced bubble method at 278.15 to 338.15 ± 0.05  K . In terms of standard addition method, the surface tension of pure IL C5MIBF4 was obtained. The properties of surface for pure C5MIBF4 were discussed in terms of the principle of independent surface action and Glasser's theory of lattice energy. Using the surface tension data, the interstice model was examined.
Keywords: Ionic liquid; Standard addition method; Surface tension;

The role of self-assembled monolayers in dictating the arrangement of molecules at the interface in a developing solid is explored. A self-assembled monolayer incorporating a complementary backbone structure between chemisorbed and crystallizing molecules of 4-hydroxybiphenyl favors its crystallization in a new monoclinic crystal packing arrangement.Molecular recognition at the interface of a SAM influences crystallization of 4-hydroxybiphenyl in the monoclinic polymorph.