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Electrical Double Layer (electrical + double_layer)
Selected AbstractsCoupled lattice-Boltzmann and finite-difference simulation of electroosmosis in microfluidic channelsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 5 2004Dzmitry Hlushkou Abstract In this article we are concerned with an extension of the lattice-Boltzmann method for the numerical simulation of three-dimensional electroosmotic flow problems in porous media. Our description is evaluated using simple geometries as those encountered in open-channel microfluidic devices. In particular, we consider electroosmosis in straight cylindrical capillaries with a (non)uniform zeta-potential distribution for ratios of the capillary inner radius to the thickness of the electrical double layer from 10 to 100. The general case of heterogeneous zeta-potential distributions at the surface of a capillary requires solution of the following coupled equations in three dimensions: Navier,Stokes equation for liquid flow, Poisson equation for electrical potential distribution, and the Nernst,Planck equation for distribution of ionic species. The hydrodynamic problem has been treated with high efficiency by code parallelization through the lattice-Boltzmann method. For validation velocity fields were simulated in several microcapillary systems and good agreement with results predicted either theoretically or obtained by alternative numerical methods could be established. Results are also discussed with respect to the use of a slip boundary condition for the velocity field at the surface. Copyright © 2004 John Wiley & Sons, Ltd. [source] Long-range and short-range mechanisms of hydrophobic attraction and hydrophilic repulsion in specific and aspecific interactionsJOURNAL OF MOLECULAR RECOGNITION, Issue 4 2003Carel Jan van Oss Abstract Among the three different non-covalent forces acting in aqueous media, i.e. Lifshitz,van der Waals (LW), Lewis acid,base (AB) and electrical double layer (EL) forces, the AB forces or electron,acceptor/electron,donor interactions are quantitatively by far the predominant ones. A subset of the AB forces acting in water causes the hydrophobic effect, which is the attraction caused by the hydrogen-bonding (AB) free energy of cohesion between the water molecules which surround all apolar as well as polar molecules and particles when they are immersed in water. As the polar energy of cohesion among water molecules is an innate property of water, the hydrophobic attraction (due to the hydrophobic effect) is unavoidably always present in aqueous media and has a value of ,Ghydrophobic,=,,102,mJ/m2, at 20,°C, being equal to the AB free energy of cohesion between the water molecules at that temperature. The strong underlying hydrophobic attraction due to this effect can, however, be surmounted by very hydrophilic molecules and particles that attract water molecules more strongly than the free energy of attraction of these molecules or particles for one another, plus the hydrogen-bonding free energy of cohesion between the water molecules, thus resulting in a net non-electrical double layer repulsion. Each of the three non-covalent forces, LW, AB or EL, any of which can be independently attractive or repulsive, decays, dependent on the circumstances, as a function of distance according to different rules. These rules, following an extended DLVO (XDLVO) approach, are given, as well as the measurement methods for the LW, AB and EL surface thermodynamic properties, determined at ,contact'. The implications of the resulting hydrophobic attractive and hydrophilic repulsive free energies, as a function of distance, are discussed with respect to specific and aspecific interactions in biological systems. The discussion furnishes a description of the manner by which shorter-range specific attractions can surmount the usually much stronger long-range aspecific repulsion, and ends with examples of in vitro and in vivo effects of hydrophilization of biopolymers, particles or surfaces by linkage with polyethylene oxide (PEO; also called polyethylene glycol, PEG). Copyright © 2003 John Wiley & Sons, Ltd. [source] Drag enhancement of aqueous electrolyte solutions in turbulent pipe flowASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2007E. Benard Abstract Experimental measurements have indicated that drag enhancement occurs when aqueous electrolyte solutions are flowing in the turbulent regime. The primary electroviscous effect due to the distortion by the shear field of the electrical double layer surrounding the ions in solution is invoked to explain the drag enhancement. Calculations using the Booth model for symmetrical one-to-one electrolytes enabled the increased viscosity in the turbulent regime to be calculated. Copyright © 2007 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Voltammetric Manifestation of the Ultraslow Dynamics at the Interface between Water and an Ionic Liquid,CHEMPHYSCHEM, Issue 13 2010Prof. Takashi Kakiuchi Abstract The ultraslow relaxation (on the order of minutes) of the electrical double-layer structure, related to a change in the phase-boundary potential across the interface between water (W) and the ionic liquid (IL) trioctylmethylammonium bis(nonafluorobutanesufonyl)amide ([TOMA+][C4C4N,]) (Y. Yasui et al., J. Phys. Chem. B. 2009, 113, 3273), appears to be invisible in the transfer of tetrapropylammonium ions across the [TOMA+][C4C4N,]|W interface, provided that the charging current, which shows an unusual dependence on the voltage scan rate, is subtracted to obtain the faradaic current. This counterintuitive observation can be explained by the differences in the timescales of the fast and slow components of the relaxation dynamics of the electrical double layer on the IL side (ms and min). In contrast, the effect of the slow dynamics becomes surfaced in ion-transfer voltammetry when the ion is surface-active. The transfer of pentadecafluorooctanoate across the [TOMA+][C4C4N,]|W interface is irreversible, which is attributable to the self-inhibition of pentadecafluorooctanoate ions transferred to the IL phase. This process is likely to be affected by the ultraslow structural change of the IL side of the interface. [source] Study on the Radius of an Electrical Spherical Micelle: Functional Theoretical ApproachCHINESE JOURNAL OF CHEMISTRY, Issue 4 2004Zheng-Wu Wang Abstract For the purpose of eliminating restriction, the Poisson-Boltzmann (PB) equation, which represents the potential of the electrical double layer of spherical micelles, can be solved analytically only under the lower potential condition, a kind of iterative method in functional analysis theory has been used. The radius of the spherical particle can be obtained from the diagram of the second iterative solution of the potential versus the distance from the center of the particle. The influences of the concentration of the ions, the charge number of ions, the aggregation number of the particle, the dielectric constant of solvent and the temperature of system on the radius also have been studied. [source] Decreasing effective nanofluidic filter size by modulating electrical double layers: Separation enhancement in microfabricated nanofluidic filtersELECTROPHORESIS, Issue 23 2008Hansen Bow Abstract Conventional methods for separating biomolecules are based on steric interactions between the biomolecules and randomly oriented gel fibers. The recently developed artificial molecular sieves also rely on steric interactions for separation. In this work, we present an experimental investigation of a method that can be used in these sieves to increase separation selectivity and resolution. This method exploits the electrostatic repulsion between the charged molecules and the charged nanofluidic structure. Although this method has been mentioned in the previous work, it has not been examined in detail. We characterize this method by comparing the selectivity with that achieved in devices with different dimensions. The results of this study are relevant to the optimization of chip-based gel-free biomolecule separation and analysis. [source] Emulsifying properties of gum kondagogu (Cochlospermum gossypium), a natural biopolymerJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 8 2009Ganga Modi Naidu Vegi Abstract BACKGROUND: Natural polymers are widely used as emulsifying agents in the food and pharmaceutical industries because of their low cost, biocompatibility and non-toxic nature. In the present study, emulsifying properties of the novel natural biopolymer gum kondagogu (GKG) were investigated. GKG solutions of different concentrations (0.1,0.6% w/v) were prepared in water and emulsified with liquid paraffin oil (40% v/v) in a high-speed homogeniser. Flow properties of the emulsions were measured using a rheometer. Emulsion stability and droplet size distribution were determined by visual observation, photomicrography and laser-scattering particle size distribution analysis. RESULTS: The emulsions prepared with GKG showed pseudoplastic behaviour. The size of oil droplets and the viscosity of emulsions at concentrations of 0.4,0.6% w/v showed little change over time (up to 30 days), indicating that the emulsions were stable. Measurements of the zeta potential of emulsions adjusted to different pH, with and without added electrolyte, showed that the stabilisation of emulsions with GKG was due to mutual repulsion between electrical double layers of particles and adsorption of macromolecules on oil droplets. CONCLUSION: The results of this experimental investigation show that GKG is a good emulsifying agent even at low concentrations, with many potential applications in the food and pharmaceutical industries. Copyright © 2009 Society of Chemical Industry [source] Theory of Ion Transport in Electrochemically Switchable Nanoporous Metallized MembranesCHEMPHYSCHEM, Issue 1 2009Christian Amatore Dr. Abstract A physicomathematical model of ion transport through a synthetic electrochemically switchable membrane with nanometric metal-plated pores is presented. Due to the extremely small size of the cylindrical pores, electrical double layers formed inside overlap, and thus, strong electrostatic fields whose intensities vary across the cross-sections of the nanopores are created. Based on the proposed model a relationship between the relative electrostatic energies experienced by ions in the nanopores and the potential applied to the membrane is established. This allows the prediction of transference numbers and explains quantitatively the ion-transport switching capability of such synthetic membranes. The predictions of this model agree satisfactorily with previous experimental data obtained for this type of devices by Martin and co-workers. [source] | ||||||||||