Journal of Colloid And Interface Science (v.309, #2)

Electrokinetics integrated by Hans Lyklema; Fabien Thomas; Jerome Duval; Arthur Hubbard (193).

Measurement and interpretation of electrokinetic phenomena by A.V. Delgado; F. González-Caballero; R.J. Hunter; L.K. Koopal; J. Lyklema (194-224).
In this report, the status quo and recent progress in electrokinetics are reviewed. Practical rules are recommended for performing electrokinetic measurements and interpreting their results in terms of well-defined quantities, the most familiar being the ζ-potential or electrokinetic potential. This potential is a property of charged interfaces and it should be independent of the technique used for its determination. However, often the ζ-potential is not the only property electrokinetically characterizing the electrical state of the interfacial region; the excess conductivity of the stagnant layer is an additional parameter. The requirement to obtain the ζ-potential is that electrokinetic theories be correctly used and applied within their range of validity. Basic theories and their application ranges are discussed. A thorough description of the main electrokinetic methods is given; special attention is paid to their ranges of applicability as well as to the validity of the underlying theoretical models. Electrokinetic consistency tests are proposed in order to assess the validity of the ζ-potentials obtained. The recommendations given in the report apply mainly to smooth and homogeneous solid particles and plugs in aqueous systems; some attention is paid to nonaqueous media and less ideal surfaces.
Keywords: Electrokinetics; Electrokinetics; Electrokinetics; Dielectric dispersion; Permittivity; Electroacoustics; Conductivity; Surface conductivity; Zeta potential; Aqueous and nonaqueous systems;

Electrokinetic investigation of surfactant adsorption by C. Bellmann; A. Synytska; A. Caspari; A. Drechsler; K. Grundke (225-230).
Fuerstenau [D.W. Fuerstenau, in: M.L. Hair (Ed.), Dekker, New York, 1971, p. 143] has already discussed the role of hydrocarbon chain of surfactants, the effect of alkyl chain length, chain structure and the pH of the solution on the adsorption process of surfactants. Later Kosmulski [M. Kosmulski, Chemical Properties of Material Surfaces, Surfactant Science Series, vol. 102, Dekker, New York, Basel, 2001] included the effect of surfactant concentration, equilibration time, temperature and electrolyte in his approaches. Certainly, the character of the head groups of the surfactant and the properties of the adsorbent surface are the basis for the adsorption process. Different surfactants and adsorbents cause different adsorption mechanisms described firstly by Rosen [M.J. Rosen, Surfactants and Interfacial Phenomena, second ed., Wiley, New York, 1989]. These adsorption mechanisms and their influencing factors were studied by electrokinetic investigations. Here only changes of the charges at the surfaces could be detected. To control the results of electrokinetic investigations they were compared with results from ellipsometric measurements. In the case of surfactant adsorption the chain length was vitally important. It could be shown by the adsorption of alkyl trimethyl ammonium bromides onto polymer films spin coated at wafer surfaces. The influence of the chain length depending on surface properties of the polymer film was studied. Streaming potential measurements were applied for these investigations. The obtained results enabled us to calculate the molar cohesive free energy per mol of CH2-group in the alkaline chain of the surfactant if all other specific adsorption effects were neglected.The adsorption process of ionic surfactants onto polymer surfaces were studied by electrokinetic investigations. Different influencing factors of the adsorption mechanism are described.
Keywords: Surfactant adsorption; Surfactant aggregates; Adsorption mechanism; Electrokinetics; Streaming potential; Ellipsometry; Surface tension;

The combination of diffusion and electrophoresis NMR is applied to determine the effective charge of poly(styrene sulfonate) in solution. While electrophoresis NMR yields the electrophoretic mobility of the molecules in solution, the hydrodynamic friction is determined from diffusion NMR. From the force balance between electrostatic force and hydrodynamic friction, the effective charge of the molecule is determined free of any model. In the present study poly(styrene sulfonate) has been investigated in mixtures of water and methanol of varying composition. The lower dielectric constant in the mixtures with high methanol content results in a drastically reduced effective charge of the polyelectrolytes. The reduced effective charge along the polymer chain is the reason for a much more compact conformation of the polyelectrolyte, which is seen in a smaller hydrodynamic size of the molecule.Decreasing the dielectric constant of a mixed solvent results in a decreasing effective charge of the polyelectrolyte in solution, which in turn brings the polyelectrolyte to a more compact conformation, as seen from the reduced hydrodynamic size.
Keywords: Polyelectrolytes; Counterion condensation; Effective charge and dielectric constant; Electrophoresis NMR; PFG NMR;

The main purpose of the present paper is to investigate the effect of the normal Gaussian size distribution on the deposition of Brownian particles onto a spherical collector, by applying the Brownian dynamic simulation method and the Kuwabara flow field model with different types of DLVO interaction energy curves and the shadow effect. The simulation results show that the collection efficiency of Brownian particles always increases with a wider particle size distribution region. The same increased tendencies are also observed for the case of increasing Reynolds number and for the case of increasing the particle size to the collector size ratio. When compared to the available experimental data, the present simulation method fits well with the experimental data when the specific deposit per collector is not large.Four types of the DLVO total interaction energy curves adopted in the simulation of the present paper.
Keywords: Particle; Size distribution; Collection; Brownian motion; DLVO theory;

Tangential streaming potential as a tool in modeling of ion transport through nanoporous membranes by Anthony Szymczyk; Nicolas Fatin-Rouge; Patrick Fievet (245-252).
Tangential streaming potential (TSP) measurements have been carried out so as to assess the electrokinetic properties of the active layer of organic nanofiltration (NF) membranes. Due to the porous structure of NF membranes, cares must be taken to convert the experimental data into zeta potential. Indeed, an assumption that is implicitly made in Smoluchowski's theory (or in related approaches accounting for the surface conduction phenomenon) is that both streaming and conduction currents involved in the streaming potential process flow through an identical path. Such an assumption does not hold with porous membranes since the conduction current is expected to flow wherever the electric conductivity differs from zero. Consequently, a non-negligible share of the conduction current is likely to flow through the membrane body filled with the electrolyte solution. This phenomenon has been taken into account by carrying out a series of TSP measurements at various channel heights. Experiments have been conducted with various electrolyte solutions. The inferred zeta potentials have been further converted into membrane volume charge densities which have been used to predict the membrane performances in terms of rejection rates. The conventional NF theory, i.e. based on a steric/Donnan exclusion mechanism, has been found to be unable to describe the experimental rejection rates. Using the volume charge density of the membrane as an adjustable parameter, it has been shown that the conventional theory even predicts the opposite sign for the membrane charge. On the other hand, the experimental rejection rates have been well described by including dielectric effects in the exclusion mechanism. In this case, a noticeable lowering of the effective dielectric constant of the electrolyte solution inside pores has been predicted (with respect to the bulk value).
Keywords: Nanofiltration; Streaming potential; Rejection; Dielectric exclusion; Fixed charge;

The electrical conductivity and surface conduction of consolidated rock cores by Saad F. Alkafeef; Abdullah F. Alajmi (253-261).
A fully computerized high-pressure and high-temperature core holder device is simultaneously used to determine the electrical conductivity, zeta potential, and surface conductivity of consolidated rock cores in aqueous and nonaqueous systems. The total electrical conductivity of rock cores was determined by coupling streaming current and potential measurements. This shows that neglecting the surface conductivity K σ is crucial to converting the streaming potential into zeta potentials. It is observed that plots of the core total conductivity as a function of the electrolyte conductivity K L exhibit two behaviors. At low ionic strength, the core conductivity clearly depends on the contribution of surface conductivity behind the slip plane, whereas at higher ionic strength, the magnitude of the surface conductivity becomes negligible. The electrical conductivity of rock cores was found to be in good agreement with the O'Brien theory and the Briggs method. The contribution of the stagnant layer to the surface conductivity in nonaqueous systems has been shown to be significant. This shows that the stagnant layer displays significantly different behavior in different nonaqueous systems, depending on the core porosity and the double-layer overlap. The results indicate that the application of electrokinetics in petroleum reservoirs can provide important insights into reservoir fluid flow characterization.The core conductivity exhibits two parallel behaviors: (a) is proportional to the surface conductivity and (b) is independent of surface conductivity as the magnitude of the surface conductivity becomes negligible.
Keywords: Electrokinetic measurements; Streaming current; Streaming potential; Zeta potential; Surface conduction; Pore pressure; Porous medium;

Studies of electrochemical properties of compacted clays by concentration potential method by Andriy Yaroshchuk; Martin A. Glaus; Luc R. Van Loon (262-271).
The development of concentration (membrane) potential upon step-wise change in salt concentration has been studied for diaphragms made of various strongly compacted clays (montmorillonite, illite, kaolinite) equilibrated with 0.1 M NaCl solution. Porous ceramic filters were used to confine the clays mechanically to be able to achieve high extent of compaction (dry density ∼2000 kg/m3). A theoretical analysis has revealed that the relaxation pattern is primarily controlled by the properties of porous filters and only slightly depends on the clay properties. At the same time, quasi-stationary values of concentration potential are directly related to the electrochemical perm-selectivity of clay. This property has revealed considerable differences in the electrochemical behaviour of various clays used in this study. This has been attributed to the differences in the micro-structure of clays, in particular to the existence or nonexistence of the so-called interlayer water where cations may retain some mobility. It has also been shown that in clays with high electrochemical perm-selectivity, one can expect a strong increase in the diffusivity of cationic radio-tracers with decreasing ionic strength of equilibrium electrolyte solution. At the same time, low electrochemical perm-selectivity means no noticeable dependence of this kind. The correctness of this observation has been corroborated by the comparison of our findings with the literature data on the diffusion of cationic radio-tracers through compacted montmorillonite (high perm-selectivity) and kaolinite (low perm-selectivity). To check the self-consistency of our approach, we have also carried out sample measurements of diffusion of cationic and anionic radio-tracers through compacted illite. It has been found that the measured effective diffusion coefficients were in excellent agreement with the electrochemical perm-selectivity estimated for this clay from the measurements of concentration potential.
Keywords: Compacted clay; Concentration potential; Ion transport number; Transient; Radio-tracers; Diffusion;

Membrane potential across reverse osmosis membranes under pressure gradient by Hidetoshi Matsumoto; Yuichi Konosu; Naomichi Kimura; Mie Minagawa; Akihiko Tanioka (272-278).
Membrane potential measurement has been widely used for the characterization of ionic membranes such as ion-exchange membranes without solvent permeability. However, there have been few studies on membrane potentials across pressure-driven processes such as reverse osmosis (RO) membranes with solvent permeability. In the present study, the membrane potential across RO membranes in NaCl and MgCl2 under the pressure gradient, Δ P = 0 – 0.3 MPa, was measured. The experimental results were analyzed by the theoretical model based on the Donnan equilibrium and the extended Nernst–Planck flux equation considering the pressure effect. The theoretical values agreed well with the experimental ones. This indicates that membrane potential is useful for characterizing the effective charge density of the active layer of RO membranes under pressure gradient.In the present study, the membrane potentials across RO membranes under pressure gradient were measured in order to determine the effective charge density of active layer of RO membranes. The results were then analyzed using a theory based on the Donnan equilibrium and the extended Nernst–Planck equation the considering pressure effect.
Keywords: Reverse osmosis membrane; Zeta potential; Membrane potential; Pressure gradient; Effective charge density;

Influence of the electrical interface properties on the rheological behavior of sonicated soy lecithin dispersions by M.A. Alvarez; D. Seyler; S. Madrigal-Carballo; A.O. Vila; F. Molina (279-282).
A significant effect, on the rheological behavior, due to the electrical properties of vesicles formed from concentrated soy lecithin dispersions have been studied in this work. The rheopectic behavior of concentrated soy lecithin dispersions (120, 150, 180, 210 and 240 g L−1) prepared by swelling–light sonication–freezing–unfreezing procedure is studied and it is specially emphasized on the transition under steady shear from lamellar phase of planar sheets to closed structures as multilamellar vesicles. Samples have been exposed to a different number of sonication cycles (from 0 to 100) and the changes in the hysteresis loop area, the apparent viscosity and the electrophoretic mobility have been studied. When the number of sonication cycles increases, the size and number of bilayers of these multilamellar vesicles decrease and therefore the total number of the vesicles and the volume fraction occupied by them show an increase.Zeta-potential variation of vesicles segregated from different defrosted and diluted (3 g L−1) soy lecithin dispersions with the number of sonication cycles.
Keywords: Soy lecithin; Vesicles; Sonication; Rheopexy; Rheology; Zeta-potential; Viscosity;

It is shown that the fundamental expression for the complex permittivity ε s ∗ of a dilute suspension of monodispersed, spherical particles, ε s ∗ = ε e ∗ ( 1 + 3 ϕ d ∗ ) , where ε e ∗ is the complex permittivity of the suspending medium and d ∗ the dipolar coefficient, is strictly valid for any value of the volume fraction ϕ of particles in the suspension, provided that d ∗ is interpreted as the ensemble average value of the dipolar coefficient of the particles and is defined in terms of the macroscopic electric field in the suspension.The fundamental expression for the complex permittivity ε s ∗ of a dilute suspension of particles in a suspending medium ε e ∗ : ε s ∗ = ε e ∗ ( 1 + 3 ϕ d ∗ ) is strictly valid for any value of the volume fraction ϕ, provided that the dipolar coefficient d ∗ is interpreted as the ensemble average value of the particles and is defined in terms of the macroscopic electric field in the suspension.
Keywords: Concentrated suspensions; Colloids; Permittivity; Conductivity; Dielectric properties;

A multiscale approach to ion diffusion in clays: Building a two-state diffusion–reaction scheme from microscopic dynamics by Benjamin Rotenberg; Virginie Marry; Jean-François Dufrêche; Eric Giffaut; Pierre Turq (289-295).
The mobility of particles is generally lowered by the presence of a confining medium, both because of geometrical effects, and because of the interactions with the confining surfaces, especially when the latter are charged. The water/mineral interface plays a central role in the dynamics of ions. The ionic mobility in clays is often understood as an interplay between the diffusion of mobile ions and their possible trapping at the mineral surfaces. We describe how to build a two-state diffusion–reaction scheme from the microscopic dynamics of ions, controlled by their interaction with a mineral surface. The starting point is an atomic description of the clay interlayer using molecular simulations. These provide a complete description of the ionic dynamics on short time and length scales. Using the results of these simulations, we then build a robust mesoscopic (Fokker–Planck) description. In turn, this mesoscopic description is used to determine the mobility of the ions in the interlayer. These results can then be cast into a diffusion–reaction scheme, introducing in particular the fraction of mobile ions, or equivalently the distribution coefficient K d . This coefficient is of great importance in characterizing electrokinetic phenomena in porous materials.A strategy to coarse-grain ion dynamics in clays: From a molecular description (left), a mesoscopic model is derived (middle), which is the basis for a diffusion/reaction scheme (right).
Keywords: Clay; Ion transport; Diffusion; Two-state; Multiscale; Coarse-graining;

Electrokinetics in extremely bimodal suspensions by M.L. Jiménez; F.J. Arroyo; A.V. Delgado; F. Mantegazza; T. Bellini; R. Rica (296-302).
Prompted by the results obtained by Mantegazza et al. [Nature Physics 1 (2005) 103], where the electric birefringence of suspensions of elongated particles was strikingly affected by the presence of a sea of very small (size ratio lower than 10:1) colloidal spheres, we have undertaken an investigation of other electrokinetic phenomena in suspensions containing various relative concentrations of large (Teflon or polystyrene latex) and small (nanometer-sized silica spheres) colloids. We have determined the quantities that might be greatly affected by the size distribution of the particles, mainly in the presence of ac electric fields, since the response of the suspensions will show very characteristic relaxations, dominated in principle by the size of the particles. In this work, we report on measurements of the dielectric dispersion of mixed particles as a function of the concentration, ionic strength, and field frequency. The results indicate that the response is not just a simple combination of those obtained with suspensions of the individual particles, and in fact the presence of even small amounts of the small particles affects considerably the frequency response of the suspensions.The amplitude of the α-relaxation decreases upon addition of silica nanoparticles (left). The electrolyte gradient around the large particle is disturbed by the electrolyte gradients around the small ones (right).
Keywords: Electric permittivity; Bimodal suspensions; Concentrated suspensions;

Experimental and theoretical evidence of overcharging of calcium silicate hydrate by Christophe Labbez; André Nonat; Isabelle Pochard; Bo Jönsson (303-307).
Electrokinetic measurements such as electrophoresis may show an inversion of the effective surface charge of colloidal particle called overcharging. This phenomenon has been studied by various theoretical approaches but up to now very few attempts of confrontation between theory and experiment have been conducted. In this work we report electrophoretic measurements as well as Monte Carlo simulations of the electrokinetic potential for the surface of calcium silicate hydrate (C―S―H), which is the major constituent of hydrated cement. In the simulations, the surface charge of C―S―H nanoparticles in equilibrium with the ionic solution is determined by a single site characteristic and electrostatic interactions between all explicit charges at the surface and in the electric double layer. We will show that ordinary electrostatic interactions are enough to describe all experimental observations. Actually, an excellent agreement is found between experimental and simulated results without any fitting parameter, both with respect to surface titration and electrokinetic behaviour. The agreement extends over a wide range of electrostatic coupling, from a weakly charged surface with mainly monovalent counter-ions to a highly charged one with divalent counter-ions.
Keywords: Overcharging; Calcium silicate hydrate; Monte Carlo simulation; Surface charge titration; Zeta potential;

Nonstationary electro-osmotic flow in closed cylindrical capillaries. Theory and experiment by N.A. Mishchuk; A.V. Delgado; S. Ahualli; F. González-Caballero (308-314).
Both from the experimental and theoretical viewpoints it is of fundamental importance to know precisely which are the fluid flow characteristics in a (cylindrical, say) closed cell under the action of an externally applied electric field, parallel to the cell axis. This is so because in many cases the experimental determination of the electrophoretic mobility of dispersed particles is carried out in closed cells, whereby the motion of the particles in the laboratory reference system is the result of the superposition of their electrophoretic migration plus the liquid motion with respect to the cell. This makes it of utmost importance to analyze the above-mentioned fluid and particle movements. If, in particular, this evaluation is carried out in the presence of alternating fields of different frequencies, information about the dynamics and time scales of the processes involved can be obtained for different frequencies of the applied field. In the present contribution, we discuss experimental results based on the determination of the velocity of polystyrene latex particles in a closed, cylindrical electrophoresis cell, and compare them to our previous theoretical analysis of the problem. It is concluded that the theory explains with great accuracy the observed particle velocities. In addition to the use of the particles as probes for the fluid velocity distribution, this work intends to give additional clues on the frequencies and positions for which electrophoretic mobility measurements in closed cells can be more reliable.The theory elaborated for the evaluation of the velocity (combined electrophoresis and electro-osmosis) of a particle in a closed cylindrical cell reproduces the experimental data accurately.
Keywords: Back flow; Closed capillary; Electro-osmosis; Electrophoresis; Stepwise pulses; Velocity profiles;

Salt concentration and particle density dependence of electrophoretic mobilities of spherical colloids in aqueous suspension by Holger Reiber; Tetyana Köller; Thomas Palberg; Felix Carrique; Emilio Ruiz Reina; Roberto Piazza (315-322).
Using laser Doppler velocimetry in the superheterodyne mode, we conducted a systematic study of the electrophoretic mobility of dispersions of small silica spheres ( a = 18   nm ) suspended in water at different salinities and particle concentrations. The concentration of NaCl was varied from 40 μM up to 16 mM, while the particle concentrations were varied between 4.2 × 10 18 and 2.1 × 10 20   m −3 . We find a decrease of mobility with increasing salt concentrations and an increase with increased particle number densities. The latter observation is not backed by the standard cell model of electrophoresis with Shilov–Zharkikh boundary conditions. Rather, if the experimental data are interpreted within that model, an unexpected change of the zeta potential at constant added salt concentration results. Interestingly, all experimental data collapse onto a single master curve, if plotted versus the ratio C ∗ of particle counterions to added salt ions. We obtain a logarithmic increase of mobility for C ∗ < 1 and a plateau for C ∗ > 1 . This may indicate a change of the Stern layer structure not yet included in the theoretical model.Experimental electrophoretic mobilities collapse to a single curve that increases approximately linearly in a semilogarithmic plot versus the ratio C ∗ of particle counterions to added electrolyte ions.
Keywords: Electrophoresis; Silica particles; SEM; Superheterodyne laser Doppler velocimetry; Electrophoretic mobility; Zeta potential;

A linear analysis of the effect of Faradaic currents on traveling-wave electroosmosis by Antonio Ramos; Antonio González; Pablo García-Sánchez; Antonio Castellanos (323-331).
Net fluid flow of electrolytic solutions induced by a traveling-wave potential applied to an array of co-planar interdigitated microelectrodes has been reported. At low applied voltages the flow is driven in the direction of the traveling-wave potential, as expected by linear and weakly nonlinear theoretical studies. The flow is driven at the surfaces of the electrodes by electrical forces acting in the diffuse electrical double layer. The pumping mechanism has been analyzed theoretically under the assumption of perfectly polarizable electrodes. Here we extend these studies to include the effect of Faradaic currents on the electroosmotic slip velocity generated at the electrode/electrolyte interface. We integrate the electrokinetic equations under the thin-double-layer and low-potential approximations. Finally, we analyze the pumping of electrolyte induced by a traveling-wave signal applied to a microelectrode array using this linear model.Traveling-wave potentials are applied to microelectrode arrays in order to pump electrolytic solutions. The fluid flow is driven at the level of the electrodes. In this paper, we include the effect of Faradaic currents in the theoretical model.
Keywords: Electroosmosis; Electrohydrodynamics; Lab-on-a-chip; Microfluidics;

The effect of step height on the performance of three-dimensional ac electro-osmotic microfluidic pumps by John Paul Urbanski; Jeremy A. Levitan; Damian N. Burch; Todd Thorsen; Martin Z. Bazant (332-341).
Recent numerical and experimental studies have investigated the increase in efficiency of microfluidic ac electro-osmotic pumps by introducing nonplanar geometries with raised steps on the electrodes. In this study, we analyze the effect of the step height on ac electro-osmotic pump performance. AC electro-osmotic pumps with three-dimensional electroplated steps are fabricated on glass substrates and pumping velocities of low ionic strength electrolyte solutions are measured systematically using a custom microfluidic device. Numerical simulations predict an improvement in pump performance with increasing step height, at a given frequency and voltage, up to an optimal step height, which qualitatively matches the trend observed in experiment. For a broad range of step heights near the optimum, the observed flow is much faster than with existing planar pumps (at the same voltage and minimum feature size) and in the theoretically predicted direction of the “fluid conveyor belt” mechanism. For small step heights, the experiments also exhibit significant flow reversal at the optimal frequency, which cannot be explained by the theory, although the simulations predict weak flow reversal at higher frequencies due to incomplete charging. These results provide insight to an important parameter for the design of nonplanar electro-osmotic pumps and clues to improve the fundamental theory of ACEO.Step height is the characteristic geometrical feature unique to nonplanar ac electro-osmotic pumps. Efficient designs may be implemented by understanding the interaction between charging dynamics and electrode geometry.
Keywords: Electrokinetics; Electro-osmosis; Microfabrication; Microfluidics; Pump;

Use of a cell model for the evaluation of the dynamic mobility of spherical silica suspensions by S. Ahualli; A.V. Delgado; S.J. Miklavcic; L.R. White (342-349).
In this paper we evaluate the validity of a cell model for the calculation of the dynamic mobility of concentrated suspensions of spheres. The key point is the consideration of the boundary conditions (electrical and hydrodynamic) at the boundary of the fluid cell surrounding a single probe particle. The model proposed is based on a universal criterion for the averages of fluid velocity, electric potential, pressure field or electrochemical properties in the cell. The calculations are checked against a wide set of experimental data on the dynamic mobility of silica suspensions with two different radii, several ionic strengths, and two particle concentrations. The comparison reveals an excellent agreement between theory and experiment, and the model appears to be extremely suitable for correctly predicting the behavior of the dynamic mobility, including the changes in the zeta potential, ζ, with ionic strength, the frequency and amplitude of the Maxwell–Wagner–O'Konski relaxation, and the inertial relaxation occurring at the top of the frequency range accessible to our experimental device.The cell model proposed for the dynamic mobility of concentrated suspensions describes very accurately the behavior for different particle sizes and volume fractions.
Keywords: Electrokinetic cell models; Concentrated suspensions; Dynamic mobility; Electroacoustic methods; Silica particles;

More often than not, the measurement of interfacial potentials by means of electrokinetic techniques is affected by interfering processes that may relax or even annihilate their primary response function. Among these processes are faradaic ones, provided that the substrate is sufficiently conducting and a redox function is available, and non-faradaic ones, if geometrical constraints are in effect. Ample experimental evidence is available, e.g., in the collapse of streaming potentials generated by metal/electrolyte solution interfaces, the bipolar microelectrodic redox processes in fluidized beds of metallic particles, and the “superfast” electrophoresis of dispersed ion exchanger particles and electron-conducting particles. Common feature of these apparently disparate phenomena is that the lateral electric field is affected by coupling with transversal depolarization fields, or by conductance gradients due to Donnan effects. Recent work has rigorously analyzed the deformation of the lateral electric field in a (streaming potential) slit cell by electron transfer reactions at the interface, taking into account both convective diffusion of the electroactive species and kinetics of the interfacial electron transfer reaction. Here a common, generic basis for faradaic and non-faradaic double layer depolarization is formulated along the lines set by Onsager, and methodologies for retrieving the underlying electrokinetic parameters from experimental data are evaluated. Particular attention is paid to the limitations of double layer polarization, as posed by the substrate.A common, generic basis for faradaic and non-faradaic double layer depolarization is formulated along the lines set by Onsager, and methodologies for retrieving the underlying electrokinetic parameters from experimental data are evaluated. Particular attention is paid to the limitations of double layer polarization as posed by the substrate.
Keywords: Bipolar faradaic processes; Onsager relations; Superfast electrophoresis; Streaming potential of metals;

Charging and swelling of cellulose films by Uwe Freudenberg; Ralf Zimmermann; Kati Schmidt; Sven Holger Behrens; Carsten Werner (360-365).
Charging and swelling of cellulose in aqueous environments are of highest interest with respect to the performance of cellulose based products and applications. To unravel the interplay between ionization and structural features of the biopolymer hydrogel we compared non-crosslinked and crosslinked cellulose thin films based on a determination of the Donnan potential [S.S. Dukhin, R. Zimmermann, C. Werner, J. Colloid Interface Sci. 274 (2004) 309] from microslit electrokinetic (streaming potential/streaming current) experiments and layer thicknesses from ellipsometry in aqueous electrolyte solutions. The pH dependence of the Donnan potential, reflecting the ionization of carboxylic acid groups within the cellulose films, was found to be significantly different from the related trend of the streaming current which reflects the characteristics of the topmost surface of the layers: While carboxylic acid groups on the surface of the films dissociate as isolated functionalities, the electrostatic interactions of ionized groups within the cellulose layers cause an incomplete dissociation (pK shift) of the carboxylic acid and a layer expansion (swelling) in the alkaline pH range. The system was found to restrict its volume charge density even after structural restrictions (crosslinking) of the layer and at lower ionic strength of the solutions through a further decrease of the degree of dissociation of the carboxylic acid functions. These findings were attributed to the local accumulation of the carboxylic acid groups caused by preferential oxidation of the amorphous regions of the cellulose and to the ordered water structure within the layer.Charging and swelling of cellulose films were studied in aqueous electrolyte solutions. For that aim the surface conductivity, Donnan potential and layer thickness were investigated by microslit electrokinetic experiments and ellipsometry.
Keywords: Cellulose; Donnan potential; Surface conductivity; Swelling;

Radiofrequency dielectric loss relaxation in polyion-induced liposome aggregates by F. Bordi; C. Cametti; S. Sennato; D. Viscomi (366-372).
In this note, we present a set of dielectric loss relaxation measurements of aqueous charged liposome suspensions during the whole aggregation process induced by oppositely charged adsorbing polyions. The system experiences two concomitant effects known as “reentrant condensation” and “charge inversion,” resulting in the formation of liposome aggregates whose average size reaches a maximum in the vicinity of the electroneutrality condition, accompanied to a progressive reduction of their overall electrical charge. Far from the neutrality, from both sides, polyion-coated liposomes exist with a charge of opposite sign. The dielectric loss relaxation in these complex aggregating systems has never been measured so far and we report here, for the first time, the dielectric loss behavior of liposomes built up by a cationic lipid and stuck together by poly(acrylate), which is a flexible oppositely charged polyion. The data are analyzed in the framework of standard electrokinetic model theory. The evolution of the aggregation process as a function of the polyion content is mainly characterized by a counterion polarization effect, governed by the surface charge density of the aggregates and hence by the ζ-potential.
Keywords: Liposome aggregation; Dielectric properties; Charge inversion; Reentrant condensation;

Guar gum (GG) and locust bean gum (LBG) are two galactomannose polysaccharides with different mannose/galactose ratio which is widely used in many industrial sectors including food, textiles, paper, adhesive, paint, pharmaceuticals, cosmetics and mineral processing. They are natural nonionic polymers that are non-toxic and biodegradable. These properties make them ideal for industrial applications. However, a general lack of understanding of the interactions between the polysaccharides and solid surfaces has hindered wider application of these polymers. In this work, adsorption of locust bean gum and guar gum at the solid–liquid interface was investigated using adsorption tests, electrophoretic mobility measurements, FTIR, fluorescence spectroscopy, AFM and molecular modeling. Electrokinetic studies showed that the adsorption of GG and LBG on talc do not change its isoelectric point. In addition, GG and LBG adsorption on talc was found not to be affected by changes in solution conditions such as pH and ionic strength, which suggests a minor role of electrostatic force in adsorption. On the other hand, fluorescence spectroscopy studies conducted to investigate the role of hydrophobic bonding using pyrene probe showed no evidence of the formation of hydrophobic domains at talc–aqueous interface. Moreover, urea, a hydrogen bond breaker, markedly reduced the adsorption of LBG and GG on talc, supporting hydrogen bonding as an important role. In FTIR study, the changes in the infrared bands, associated with the C―O stretch coupled to the C―C stretch and O―H deformation, were significant and therefore also supporting hydrogen bonding of GG and LBG to the solid surface. In addition, Langmuir modeling of adsorption isotherm further suggested that hydrogen bonding is the dominant force for polysaccharide adsorption since the adsorption free energy of these polymers is close to that for hydrogen bond formation. From molecular modeling, different helical structures are observed for LBG and GG because of their different galactose/mannose ratio and these polymers were found to adsorb flat on solid to let more of its OH groups in contact with the surface. All of the above results suggest that the main driving force for adsorption both of GG and LBG on talc is hydrogen bonding rather than hydrophobic force even though there is difference in G/M ratio between them.The objective of this study was to clarify the mechanistic aspects of the interactions between galactomannose (guar, LBG) and talc using a combination of spectroscopic, microscopic, molecular modeling, electrostatic and adsorption techniques.
Keywords: Talc; Polysaccharide; Polymer adsorption; AFM; Model; Zeta potential; FTIR;

We studied the sequential quenching of prolate ellipsoids on a homogeneous surface by using our proposed pair potential whose repulsive part was that of hard ellipses and attractive part was the r −6 pairwise attraction. Both the strength and range parameters for the attraction were functions of the orientations of the pair of ellipses and related by ε ∝ σ − λ . The parameter λ determines the relative strength of the side-by-side and end-to-end attractions and thus plays an important role in determining the alignment of the particles. We adopted the value λ = 2.19 by using point-energy additivity to compute the minimum energies for both of these configurations for a pair of ellipsoids of revolution with aspect ratio of 2:1. We investigated the effect of temperature and the parameter λ on the alignments of ellipses. Both radial distribution function, g ( r ) , and orientational correlation function, G ( r ) , show the expected longer ranges of orientational correlation at lower temperatures and show higher degree of orientational order for λ = 3.5 than λ = 2.19 and 0.10. This can also be seen in the examples of configurations showing that for λ = 3.5 , ellipses are more aligned than λ = 2.19 and 0.1.
Keywords: Ellipsoid; Sequential deposition; Clustering; Monte Carlo simulation; Irreversible adsorption;

Adsorption of arsenite and arsenate onto muscovite and biotite mica by Sudipta Chakraborty; Mariette Wolthers; Debashis Chatterjee; Laurent Charlet (392-401).
Arsenite and arsenate sorption was studied on two silt-sized phyllosilicates, namely muscovite and biotite, as a function of solution pH (pH 3–8 for muscovite, and 3–11 for biotite) at an initial As concentration of 13 μM. The amount of arsenic adsorbed increases with increasing pH, exhibiting a maximum value, before decreasing at higher pH values. Maxima correspond to 3.22 ± 0.06   mmol kg −1 As(V) at pH 4.6–5.6 and 2.86 ± 0.05   mmol kg −1 As(III) at pH 4.1–6.2 for biotite, and 3.08 ± 0.06   mmol kg −1 As(III) and 3.13 ± 0.05   mmol kg −1 As(V) at pH 4.2–5.5 for muscovite. The constant capacitance surface complexation model was used to explain the adsorption behavior. Biotite provides greater reactivity than muscovite toward arsenic adsorption. Isotherm data obeyed the Freundlich or Langmuir equation for the arsenic concentration range 10−7–10−4 M. Released total Fe, Si, K, Al, and Mg in solution were analyzed. Calculation of saturation indices by PHREEQC indicated that the solution was undersaturated with respect to aluminum arsenate (AlAsO4⋅2H2O), scorodite (FeAsO4⋅2H2O), and claudetite/arsenolite (As4O6).Arsenite and arsenate sorption onto muscovite and biotite increase with increasing pH, exhibiting a maximum value, before decreasing at higher pH values. Maxima corres pond to 3.22 ± 0.06   mmol kg −1 As(V) at pH 4.6–5.6 and 2.86 ± 0.05   mmol kg −1 As(III) at pH 4.1–6.2 for biotite, and 3.08 ± 0.06   mmol kg −1 As(III) and 3.13 ± 0.05   mmol kg −1 As(V) at pH 4.2–5.5 for muscovite. Biotite provides greater reactivity than muscovite toward arsenic adsorption.
Keywords: Arsenic; Phyllosilicate; Adsorption; Isotherm; Edge; Reactivity; Release;

Aggregation and adsorption of reactive dyes in the presence of an anionic surfactant on mesoporous aminopropyl silica by Antonio R. Cestari; Eunice F.S. Vieira; Gláucia S. Vieira; Luis E. Almeida (402-411).
A surface tension technique was used to determine the critical aggregation concentration (cac) of a yellow and a red dye in relation to the presence of the anionic surfactant sodium dodecylbenzene sulfonate (DBS) and to temperature changes in buffered aqueous solutions. The cac values of the yellow dye increase from 25 to 45 °C (from 41.37 to 50.32 mg L−1) and decrease from 45 to 55 °C (from 50.32 to 38.72 mg L−1). The cac values for the red dye/DBS aggregates decrease (from 124.52 to 88.50 mg L−1) from 25 to 55 °C. Adsorption of the two dyes onto a mesoporous aminopropyl silica (Sil–NH2) was also studied. The adsorption of the yellow dye increases with an increase in temperature from 25 to 55 °C. In the presence of DBS the adsorption on Sil–NH2 for the yellow dye decreases, and for the red dye increases from 25 to 55 °C. Adsorptions occurred below and above the cac of the anionic dyes/DBS aggregates. Adsorption of the dyes onto Sil–NH2 fitted well to the Langmuir, Freundlich, and Redlich–Peterson adsorption models. However, in the presence of DBS, only the Freundlich model fit the experimental adsorption data at low dye concentrations (less than 400 mg L−1). In this case, the Redlich–Peterson model was only fitted to the red dye adsorption data. The magnitude of the Dubinin–Radushkevich energetic parameters (E, from 7.00 to 15.00 kJ mol−1) indicates that the adsorption of the dyes onto Sil–NH2, in the absence and in the presence of DBS, is controlled by water adsorbed/dye in solution ion-exchange interactions. It is observed that the values of Δ ads H are positive for both dyes and the values are quite similar to each other. The exception is the adsorption of the yellow dye in the presence of DBS, which is slightly exothermic. The Δ ads G values are all negative. However, the interactions of the dyes with Sil–NH2 silica are more spontaneous in the presence of the surfactant. The positive adsorption entropy values ( Δ ads S ) for the interaction of the dyes suggest that entropy is a driving force of the dye adsorptions. However, the entropic contribution is higher for the adsorptions in the presence of DBS. It was suggested that the chemical structures of the dyes play an important role in the formation of the dye/DBS aggregates and in dye adsorption onto the aminopropyl silica.
Keywords: Silica gel; Aminopropyl silica; Dye/surfactant aggregations; Adsorption thermodynamics;

Mean grain sizes and specific surface areas (SSAs) of ice substrates formed by vapor deposition at low temperatures are of importance in simulating external surfaces of icy satellites in the solar system. Environmental scanning electron microscopy (ESEM) was used to obtain granule sizes and to observe the phase of ice granules prepared on borosilicate, silicon, and metallic plates. Ices prepared at a temperature lower than 140 K appear to be amorphous, and their granule sizes are typically submicrometer. At slightly warmer temperatures, near 180–200 K, ice films are composed of either hexagonal or cubic granules with sizes up to a few micrometers. When briefly annealed to even warmer temperatures, ice granule sizes approach ∼ 10   μm . SSAs of ice substrates were determined from BET (Brunauer, Emmett, and Teller) analysis of gas adsorption isotherms in the temperature range from 83.5 to 261 K. SSAs decrease drastically from 102 m2/g at 83.5 K to 0.87 m2/g at 150 K and further decrease slowly to 0.22 m2/g at 261 K, suggesting that the transition from amorphous to crystalline forms occurs at ∼ 150   K . The overall decrease in SSAs is primarily due to metamorphism and sintering. These results are comparable to recent field and laboratory measurements. Possible implications for theoretical models of icy satellites of outer planets using remote sensing techniques are also discussed.
Keywords: Ices; Grain sizes; Surface areas; Porosity; Sintering; Metamorphism;

The transport of aromatic carboxylate compounds in the environment can be strongly influenced by adsorption onto certain minerals, such as iron oxides and hydroxides, found in ground water and soils. Batch experiments with five iron oxides were conducted to quantify the contributions to adsorption from different iron mineral surfaces and compare adsorption characteristics of selected organic acids (gentisic acid (GA) and 1-hydroxy-2-naphthoic acid (HNA)). Because of their widespread abundance in soils and sediments, goethite, lepidocrocite, ferrihydrite, hematite, and magnetite were investigated. Sorption of two organic acids onto iron oxides was examined over a wide range of conditions (pH, ionic strength, and sorbate concentration). Specific surface area and mineral surface charge proved be important for the adsorption of these compounds. The sorption isotherm was described well by the Tempkin equation for both organic acids, with the adsorption constant higher for HNA than GA. For modeling the sorption edges of ferrihydrite and hematite, surface reactions involving the formation of mononuclear (1:1) surface species were proposed. These results indicate that the generalized two-layer model, with the assumption of homogeneous surface sites, could predict sorption on iron oxides over a range of pH conditions. The results of this study suggest that the mineralogy of the iron oxides and the pH value should be considered when predicting sorption of aromatic acids onto iron oxides and their fate in the soil and the environment.The binding of two aromatic acids onto ferrihydrite (F) and hematite (H) can be described by surface complexation modeling by assuming one type of site and both monodentate and bidentate complexes. The figure shows the sorption data as a function of pH for both HNA and GA and model predictions (solid lines).
Keywords: Aromatic compounds; Iron oxides; Sorption; Surface complexation modeling;

The effect of activated carbon fiber (ACF) on the ozonation of phenol in water in a fluid bed reactor was investigated. It was observed that this combined process could increase the yield of the oxidation process significantly for phenol and COD (chemical oxygen demand) removal, especially for the phenol removal. The efficiency of ozonation increased with an increase in the dose of ACF. Higher initial phenol concentration only caused a slight decrease of phenol and COD removal. The results of repeated use found that ozonation could efficiently regenerate ACF in situ in the reactor, which was considered easy to handle without the costly ex situ regeneration of the industrial treatment process. The Boehm titrations and FTIR studies indicate that the ozonation process in water can significantly change the composition of acidic surface oxygen-containing groups of ACF, leading to the increase of carboxylic, hydroxylic, and carbonylic groups and the slight decrease of the lactonic groups. Furthermore, this process can also increase the surface area and total pore volume of ACF. Due to the new micropore formation and some pore enlargement, the micropores became smaller, and the mesopores and macropores got bigger.The effect of the ACF amount on the phenol and COD removal in the ozonation of phenol in water.
Keywords: Catalytic ozonation; Phenol; ACF adsorption; ACF regeneration;

Partial molar volume of anionic polyelectrolytes in aqueous solution by Constain Salamanca; Martín Contreras; Consuelo Gamboa (435-439).
In this work the partial molar volumes ( V ) of different anionic polyelectrolytes and hydrophobically modified polyelectrolytes (PHM) were measured. Polymers like polymaleic acid-co-styrene, polymaleic acid-co-1-olefin, polymaleic acid-co-vinyl-2-pyrrolidone, and polyacrylic acid (abbreviated as MAS-n, PA-n-K2, AMVP, and PAA, respectively) were employed. These materials were investigated by density measurements in highly dilute aqueous solutions. The molar volume results allow us to discuss the effect of the carboxylic groups and the contributions from the comonomeric principal chain. The PAA presents the smaller V, while the largest V value was for AMVP. The V of PHM shows a linear relationship with the number of methylene groups in the lateral chain. It is found that the magnitude of the contribution per methylene group decreases as the hydrophobic character of the environment increases.This figure shows an anionic polyelectrolyte hydrophobically modified by its counterion in aqueous solutions adopting a nonextended conformation.
Keywords: Specific volumes; Partial molar volume; Hydrophobically modified polyelectrolytes;

Smoluchowski's coagulation equation is studied for the kernel K ( u , v ) = E ( u α v β + u β v α ) with real, non-negative α, β and E, using gamma distributions with a singularity at zero volume as initial size spectra. As the distribution parameter of the gamma distribution, p, approaches its lower limit ( p → 0 ) the distribution becomes ∼ p v p − 1 for small v. Asymptotic solutions to the coagulation equation are derived for the two cases p → 0 and v → 0 . The constant kernel ( α = β = 0 ) is shown to be unique among the studied kernels in the sense that the p → 0 asymptote and the v → 0 asymptote differ.Asymptotic solutions to the Smoluchowski's coagulation equation using singular gamma distributions (i.e., the distribution parameter 0 < p < 1 ) as initial size spectra are derived. The constant kernel has different p → 0 and x → 0 asymptotes.
Keywords: The Smoluchowski coagulation equation; Exact solutions; Gamma distribution;

Clay soils have specific properties that cause difficulty in the assessment and remediation of contaminated sites. Furthermore, polyaromatic hydrocarbons, when present in soil, are difficult to extract due to their nonpolar, high molecular weight characterization. In this study, the supercritical fluid (carbon dioxide) extraction (SFE) technique, with and without methanol modifier, was used for removal of PAHs (phenanthrene) from kaolinite, illite, and montmorillonite soils. The impact of SFE parameters (fluid pressure, fluid temperature, and time), and of clay properties (such as clay minerals content, initial moisture content, soil porosity or equivalent pores size, clay surface area, cation-exchange capacity, and clay-swelling index) on the removal efficiency of PAHs from clayey soils were investigated. The results of this investigation were used to develop a semi-empirical correlation between the recovery (i.e. the extraction efficiency) at any time and above mentioned parameters and properties.
Keywords: Clayey soil; Kaolinite; Illite; Montmorillonite; Supercritical fluid extraction (SFE); Phenanthrene; Porosity; Surface area; Cation-exchange capacity; Swelling index; Prediction; Extraction efficiency;

Emulsion copolymerization of poly(methacrylic acid) and poly(2-(diethylamino)ethyl methacrylate) (PMAA/PDEA) yielded pH-responsive polyampholyte microgels of 200–300 nm in diameter. These microgels showed enhanced hydrophilic behavior in aqueous medium at low and high pH, but formed large aggregates of ∼2500 nm at intermediate pH. To achieve colloidal stability at intermediate pH, a second batch of microgels of identical monomer composition were synthesized, where monomethoxy-capped poly(ethylene glycol)methacrylate (PEGMA) was grafted onto the surface of these particles. Dynamic light-scattering measurements showed that the hydrodynamic radius, R h , of sterically stabilized microgels was approximately 100 nm at intermediate pH and increased to 120 and 200 nm at pH 2 and 10, respectively. Between pH 4 and 6, these microgels possessed mobility close to zero and a negative second virial coefficient, A 2 , due to overall charge neutralization near the isoelectric pH. From the R h , mobility, and A 2 , cross-linked MAA–DEA microgels with and without PEGMA retained their polyampholytic properties in solution. By varying the composition of MAA and DEA in the microgel, it is possible to vary the isoelectric point of the colloidal particles. These new microgels are being explored for use in the delivery of DNA and proteins.The cloudy region near the IEP indicates that PMAA-co-PDEA polyampholyte microgels became more compact due to charge neutralization. The solution is transparent below and above the cloudy region due to presence of positive DEA groups and negatively charged carboxylic groups.
Keywords: Emulsion polymerization; pH-responsive polyampholyte microgel; Isoelectric pH; Steric stabilization;

Photochemical degradation of the hazardous dye Safranin-T using TiO2 catalyst by V.K. Gupta; Rajeev Jain; Alok Mittal; Megha Mathur; Shalini Sikarwar (464-469).
Aqueous solutions of Safranin-T, a hazardous textile dye, are photodegraded under ultraviolet light using TiO2 as catalyst. The process has been carried out at different pHs, amounts of catalyst, concentrations of the dye, and effects of the electron acceptor H2O2. It is found that under the influence of TiO2 as catalyst the colored solution of the dye Safranin-T becomes colorless and the process follows first-order reaction kinetics. The optimum conditions for the degradation of the dye have been found as 5.0 × 10 −5  M dye concentration, pH 5.7, and 12 mg catalyst dose. In order to evaluate the effect of the electron acceptor, the effect of H2O2 on the degradation process is also monitored and it is found that generation of hydroxyl radicals and retardation of electron–hole recombination takes place. Measuring chemical oxygen demand also monitors the toxicity of the degraded dye solution and a significant decrease is observed, which implies that the photodegradation through TiO2 is a safer technique.Anatase titanium dioxide is a suitable catalyst for photochemical degradation due to its large band gap (around 3.2 eV). Complete mineralization of the adsorbed Safranin-T has been achieved with TiO2.
Keywords: Safranin-T; Photocatalytic; Degradation; TiO2; UV light; COD;

Corrosion of copper in aerated synthetic sea water (3.5% NaCl) solutions and its inhibition by 3-amino-1,2,4-triazole (ATA) have been studied using electrochemical, gravimetric, and pH measurements, along with Raman spectroscopy. Electrochemical measurements indicated that the presence of ATA and the increase of its concentration suppress the corrosion process on the copper surface. This effect decreases cathodic, anodic, and corrosion ( j corr ) currents and corrosion rates ( K corr ), while increasing polarization resistance ( R p ), surface coverage (θ), and inhibition efficiency (IE%). Weight loss measurements indicated that the dissolution of copper and the accompanying change of pH decreased to a minimum even after 24 days immersion due to the presence of ATA and the increase of its concentration. Raman investigations revealed that the inhibition of copper corrosion is achieved by strong adsorption of ATA molecules onto the copper surface, preventing it from being corroded easily.It is clearly seen that the increase of the immersion time of Cu from 0 (Fig. a) to 50 h (Fig. b) in sea water alone (curves 1) and in the presence of 0.5 (curves 2) and 1.0 mM 3-amino-1,2,4-triazole (curves 3) significantly decreased the cathodic, corrosion, and anodic currents.
Keywords: Synthetic sea water solutions; 3-Amino-1,2,4-triazole; Copper corrosion; Corrosion inhibitors; Raman spectroscopy;

One-pot synthesis of Ag/ZnO composites is described by a simple hydrothermal approach. In the reaction process, hexamethylenetetramine (HMT) can convert into ammonia and formaldehyde, which are used as a precipitant for the fabrication of ZnO and a reducing agent for the loading of metal Ag, respectively. The UV emission of ZnO is obviously enhanced by the deposition of silver islands on its surface. The photocatalytic characterization reveals that the composites behave high photocatalytic activity for a solution of rhodamine B. The influence of Ag+ ions on the morphology of ZnO is discussed. The composites are characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL).Ag/ZnO composites were synthesized through a simple one-pot process. The silver loading on the surface of ZnO not only promotes the UV emission obviously but also improves the photocatalytic activity for a solution of rhodamine B.
Keywords: Ag/ZnO composites; Hydrothermal synthesis; UV emission; Photocatalytic activity;

Simultaneous sorption of benzene and heavy metals onto two organoclays by Vinka A. Oyanedel-Craver; Megan Fuller; James A. Smith (485-492).
An experimental study was performed to determine the feasibility of using hexadecyltrimethylammonium bentonite clay (HDTMA-clay) and benzyltriethylammonium bentonite clay (BTEA-clay) for simultaneous sorption of benzene and one of four heavy metals (Pb, Cd, Zn and Hg). Specifically, the role of competition between benzene and each heavy metal was studied. The sorption of Pb, Cd, and Zn on both BTEA- and HDTMA-clay decreases in the presence of benzene relative to the sorption obtained without benzene present. This indicates that there is competition between Pb, Cd, and Zn and organic compounds during sorption onto both organoclays. On BTEA-clay, Cd, Pb and Zn sorption was reduced by 24, 37, and 51%, respectively. On HDTMA-clay, Cd, Pb, and Zn sorption was reduced by 25, 30, and 57%, respectively. Hg sorption was not affected either by the presence of benzene or by the organoclays used. The sorption of benzene onto BTEA-clay in the presence of Hg, Zn, Pb, and Cd was less than the sorption observed when no heavy metal was present. The presence of Hg resulted in the most significant decrease in sorption, causing a 59% reduction in benzene sorption. The presence of Zn, Pb, and Cd caused a 41, 35, and 31% reduction in benzene sorption, respectively. In general, sorption of benzene onto HDTMA-clay was not affected by the presence of the heavy metals, indicating there are no competitive effects observed with Zn, Cd, and Hg when HDTMA-clay was the sorbent. However, the presence of Pb did cause a 20% reduction in benzene sorption to HDTMA-clay. Both organoclays tested had dual sorptive properties for both heavy metals and an organic contaminant. While the competitive effects were greater for the BTEA clay, both organoclays are capable of simultaneously removing benzene and either Zn, Cd, Hg, or Pb from aqueous solution.An experimental study was performed to determine the feasibility of using hexadecyltrimethylammonium bentonite clay and benzyltriethylammonium bentonite clay for simultaneous sorption of benzene and one of four heavy metals (Pb, Cd, Zn and Hg).
Keywords: Organoclay; Heavy metals; Benzene; Sorption; Competition;

Theoretical considerations and experiments in capillary tubes suggest that blobs exhibit resonance in porous media when they are trapped because of interfacial tension. Here, we investigate the hypothesis that such blobs can be mobilized by exploiting a phenomenon entitled capillarity-induced resonance, that is, by exciting the blobs at their resonant frequency. We used Lattice–Boltzmann (LB) modeling to perform numerical experiments, and we validated the LB model using analytical solutions that approximate the linear response of blobs with pinned menisci in straight and polygonal pore channels to an oscillatory body force. The LB simulations agree well with the quasistatic response, which the analytical solutions describe correctly. Furthermore, the frequency response, particularly the resonant frequency, agrees well, even though the analytical solutions do not accurately estimate viscous pressure drops. Numerical experiments in polygonal and sinusoidal pore channels, as well as disc packings, show that blobs, which are trapped even though a constant body force is applied, can indeed be mobilized by exploiting capillarity-induced resonance. Moreover, the resonant frequency can be estimated in numerical experiments by determining the dominant frequency in the blob amplitude in response to a force pulse. This is of great practical relevance for complex geometries, for which the resonant frequency cannot be easily predicted theoretically.Nonwetting phase blobs trapped in porous media can be mobilized by excitation at their resonant frequency.
Keywords: Residual nonwetting phase; Mobilization; Porous media; Elastic waves; Two-phase flow;

Measurements have been made to determine the solubility of ethane, C2H6, in aqueous solutions of four different surfactants of the linear alkanesulfonate class at 25 °C. The surfactants, sodium 1-pentanesulfonate, sodium 1-hexanesulfonate, sodium 1-heptanesulfonate, and sodium 1-octanesulfonate, all share a common head group (―SO 3) and counter ion (Na+), and differ only in the length of the alkyl chain attached to the head group. The solubility of ethane has been determined as a function of surfactant concentration for each surfactant. At surfactant concentrations below the critical micelle concentration (CMC), the solubility of ethane is quite low and differs only slightly from the solubility of ethane in pure water. At concentrations greater than the CMC, the solubility of ethane exhibits a gradual increase with surfactant concentration. At high surfactant concentrations, well in excess of the CMC, the solubility of ethane is found to increase as a linear function of surfactant concentration. From this data it becomes possible to determine the fractional population of the surfactant in the free and micellized states. The solubility data measured for ethane is interpreted in terms of the mass-action model for micelle formation.Concentrations of sodium alkylsulfonates present in free-ion and micellar form as a function of concentration illustrating the partitioning of the surfactant molecules between the micellar and bulk aqueous phases.
Keywords: Gas solubility; Micelles; Sodium alkylsulfonates; Free surfactant; Micellization; Ethane; Aqueous solutions;

The influence of colloidal interactions on fiber network strength by A. Elisabet Horvath; Tom Lindström (511-517).
Various forces govern the fiber–fiber interaction in a flowing suspension, causing fibers to create flocs. The aim with this investigation was to examine the influence of colloidal interactions on the fiber network strength by varying surface charge density, electrolyte concentration, and type of counterion. This was accomplished by comparing surface force measurements, utilizing colloidal probe microscopy (CPM), with the apparent yield stress, using a parallel plate rheometer. Results show that by increasing the charge density by grafting carboxymethyl cellulose (CMC) to the surface, a large electrosteric repulsion is created, which gives weaker network strength. Increasing the electrolyte concentration decreases the repulsion. The network strength was, however, not affected by electrolyte concentration for untreated fibers whereas a high electrolyte concentration increased the yield stress for CMC-treated fibers. The change of counterions affect the repulsion, causing a change in network strength due to differences in the surface swelling of cellulose.The surface charge density was altered by grafting of carboxymethyl cellulose to cellulose surfaces and the interactions between the surfaces was investigated using colloidal probe microscopy and parallel plate rheometer.
Keywords: CPM; Rheometer; Colloidal interactions; Charge density; Ionic strength; Counterion; Yield stress;

One-step controlled synthesis of anisotropic gold nanostructures with aniline as the reductant in aqueous solution by Zhirui Guo; Yu Zhang; Lan Huang; Meng Wang; Jing Wang; Jianfei Sun; Lina Xu; Ning Gu (518-523).
We report a general and versatile method for controlled synthesis of anisotropic gold nanostructures through the reduction of HAuCl4 by aniline in aqueous solution, without the need for an additional stabilizer or capping agent. In this approach, the reduction kinetics of AuCl 4 can be altered by simply adjusting the initial pH and temperature, inducing the formation of a wide variety of anisotropic nanostructures such as dispersed or multilayered plates, wires with networked or paramecium-like structures, and ginger-shaped particles. AFM, TEM, XRD, EDX, FTIR, and UV–vis–NIR measurements were used to characterize the resulting gold nanostructures. Investigation reveals that in situ formed polyaniline serves effectively as a capping agent to direct the shape of gold nanostructures during the slow growth process. These as-synthesized gold nanostructures exhibit strongly shape-dependent optical properties. This facile approach may be extended to the synthesis of some other anisotropic metal nanostructures such as platinum or palladium.In the aniline reduction of HAuCl4, the reduction kinetics of AuCl 4 can be altered by varying the initial pH and temperature, inducing the formation of various anisotropic gold nanostructures.
Keywords: Gold; Anisotropic shape; Nanostructure; Aniline; pH;

Enhanced immunoresponse of antibody/mixed-PEG co-immobilized surface construction of high-performance immunomagnetic ELISA system by Yukio Nagasaki; Hiroshi Kobayashi; Yoshinori Katsuyama; Tomoko Jomura; Takeshi Sakura (524-530).
Poly(ethylene glycol) possessing pentaethylenehexamine at one end (N6-PEG) was prepared via a reductive amination reaction of aldehyde-ended PEG with pentaethylenehexamine. Using N6-PEG, an antibody/PEG co-immobilized surface was constructed on magnetic particles via an active ester reaction method. After immobilization of the antibody on the active ester surface, N6-PEG was reacted on the magnetic beads. A sandwich enzyme-linked immunosorbent assay (ELISA) system was newly constructed using PEG/antibody co-immobilized magnetic beads combined with an alkaline phosphatase (ALP)-assisted fluorescent detection system using α-fetoprotein (AFP) as a model antigen. The co-immobilization of both antibody and PEG on the magnetic bead surfaces reduced the nonspecific adsorption of proteins from cell lysates. Especially, when the magnetic particle surface was modified by N6-PEG mixtures with different molecular weights of 6000 and 2500 (6 kDa:2.5 kDa = 9:1 w/w), the nonspecific adsorption of proteins was strongly suppressed. It is rather surprising for us that the sensitivity of the antibody on the surface was enhanced significantly when the PEG tethered chain was constructed in between the surface antibodies. Consequently, the mixed N6-PEG treatment showed a much higher S/N ratio than for the corresponding beads treated with bovine serum albumin (BSA), a conventional blocking reagent. Actually, when α-fetoprotein was analyzed by the magnetic bead-assisted ELISA thus constructed, the S/N ratio was about 20-fold higher for the mixed coating with PEG (6 kDa):PEG (2.5 kDa) = 9:1, compared to the conventional BSA.PEG having pentaethylenehexamine at one end improved the blocking efficiency of antibody immobilized magnetic particle. The dense PEG tethered chain in between the surface antibodies improved the immunoresponse significantly. The obtained immunomagnetic beads can be utilized for magnetic bead-assisted ELISA.
Keywords: N6-PEG; Immunochemical enhancer; Immunomagnetic assay; Magnetic beads; Mixed PEG tethered chain; ELISA;

Alumina 8-hydroxyquinoline complexes (Alq x )/Al2O3 nano colloids have been successfully prepared by focused, pulsed laser ablation at the interface of solid Al2O3 and a flowing liquid containing 8-hydroxyquinoline (Q) and one of two polymers (polystyrene, PS, and polymethyl methacrylate, PMMA). Three factors influenced the luminescence of the (Alq x )/Al2O3 nano colloids. The first factor was whether the 8-hydroxyquinoline was added before or after laser ablation. The second factor was if the reaction medium consisted of (1) Q dissolved in ethanol, (2) Q dissolved in cyclohexane containing PS, or (3) Q dissolved in ethyl acetate containing PMMA. The third factor affecting luminescence was the age of the colloids. The (Alq x )/Al2O3 nano colloid product was characterized by transmission electron microscopy (TEM), ultraviolet visible spectroscopy (UV–vis), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and fluorescence spectroscopy. The product from all three-reaction media luminesced when irradiated with ultraviolet light. The product formed in cyclohexane containing PS gave the greatest luminescence, followed by the product formed in ethanol, and the product formed in ethyl acetate containing PMMA gave the smallest luminescence. The luminescence mechanism is similar to that of Alq3.The Alq x /Al2O3 ethanol colloids can radiate intense green light under ultraviolet radiation.
Keywords: Pulsed laser ablation; Nano colloids; (Alq x )/Al2O3 nanoparticles; Fluorescence; Flowing liquid;