Showing papers by "Jyh-Ping Hsu published in 2011"

Effects of double-layer polarization and counterion condensation on the electrophoresis of polyelectrolytes

Abstract: The electrophoretic behavior of an entirely porous, charged entity such as DNA, protein, or a synthetic polymer is modeled. Adopting a spherical polyelectrolyte on the axis of a narrow, long cylindrical pore as the model system, we show that, in addition to the effects of boundary, double-layer polarization arising from the deformation of the ionic cloud surrounding the polyelectrolyte due to the convective flow of ionic species, and electroosmotic retardation flow coming from the motion of unbalanced amount of counterions in the double layer, the effect of counterion condensation also plays a role, yielding behaviors that are different both quantitatively and qualitatively with those of the corresponding rigid and soft particles. The present analysis predicts the presence of several unexpected and interesting results. For instance, the electrophoretic mobility of the polyelectrolyte may show a local maximum as the amount of its fixed charge varies, and the amount of fixed charge at which the local maximum occurs depends upon the thickness of double layer, the relative size of the pore, and the friction coefficient of the polyelectrolyte. These findings are consistent with the experimental observations in the literature, but the relevant mechanisms have not been proposed and/or explained satisfactorily. The results gathered in this study provide valuable information for both the design of an electrophoresis apparatus and the interpretation of experimental data.

Electrophoresis of a charge-regulated sphere in a narrow cylindrical pore filled with multiple ionic species.

Abstract: The electrophoresis of a charge-regulated particle is modeled under the conditions where the dispersion medium contains multiple ionic species and the influence of a boundary can be significant. The conditions assumed in this study are much closer to reality than those of the available analyses in the literature, and, therefore, the results gathered provide valuable information to both theoreticians and experimentalists. For illustration, we consider the electrophoresis of a sphere in a cylindrical pore filled with four kinds of ionic species, namely, H(+), OH(-), Na(+), and Cl(-); these ions are usually present in experiments where the bulk pH is adjusted by HCl and NaOH. We show that the presence of the pore has the effect of inhibiting the polarization of the double layer near a particle, thereby influencing both quantitatively and qualitatively the electrophoretic behavior of the particle. If the pore is charged, then the effect of electroosmotic flow needs be considered, yielding interesting phenomena that might play a key role in practice.

Diffusiophoresis of a nonuniformly charged sphere in an electrolyte solution.

Abstract: The diffusiophoresis of a rigid, nonuniformly charged spherical particle in an electrolyte solution is analyzed theoretically focusing on the influences of the thickness of double layer, the surface charge distribution, the effect of electrophoresis, and the effect of double-layer polarization. We show that the nonuniform charge distribution on the particle surface yields complicated effect of double-layer polarization, leading to interesting diffusiophoretic behaviors. For example, if the sign of the middle part of the particle is different from that of its left- and right-hand parts, then depending upon the charge density and the fraction of the middle part, the particle can move either to the high-concentration side or to the low-concentration side. Both the diffusiophoretic velocity and its direction can be manipulated by the distribution of the surface charge density. In particular, if the electrophoresis effect is significant, then those properties are governed by the averaged surface charge density of the particle. A dipolelike particle, where its left- (right-) hand half is negatively (positively) charged, always migrates toward the low-concentration (left-hand) side, that is, it has a negative diffusiophoretic velocity. In addition, that diffusiophoretic velocity has a negative local minimum as the thickness of double layer varies.

Preparation of mineral source water from deep sea water: Reduction of sulfate ion using selemion ASV membrane

Abstract: Adopting a laboratory-scaled electrodialysis (ED) process, we investigate the performance of a monovalent anion exchange permselective membrane in the reduction of the concentration of sulfate ions during the production of mineral source water from deep sea water (DSW). The dependence of the separation efficiency of anions on the operating time and the applied DC voltage is investigated based on a brine having salinity of about 15% prepared from DSW. The experimental results reveal that if the applied DC voltage is high, the change in the liquid volume during ED is dominated by the ions transported and the effect of electroosmosis. In addition, the amount of chloride ions transported correlates roughly linearly with the operating time, and the transport of sulfate ions is found to be blocked by chloride ions, presumably because of that the pore size of the permselective layer is close to the size of sulfate ions. © 2010 American Institute of Chemical Engineers AIChE J, 2011

Electrical potentials of two identical particles with fixed surface charge density in a salt-free medium.

Abstract: The electrical potentials of two identical planar, cylindrical, and spherical particles immersed in a salt-free dispersion are solved analytically by a perturbation approach for the case of constant surface charge density. The system under consideration simulates, for example, micelles, where the ionic species in the liquid phase come mainly from the dissociation of the functional groups on the droplet surface. We show that for planar particles, the present zero-order perturbation solution is exact, and for cylindrical and spherical particles, the first-order perturbation solution provides sufficiently accurate results, with an averaged percentage deviation on the order of 1% under typical conditions. In general, the higher the surface charge density, the higher the valence of counterions, the smaller the separation distance between two particles, and the smaller the curvature of particle surface, the better the performance of the perturbation solution.

Diffusiophoresis of a Nonuniformly Charged Sphere in a Narrow Cylindrical Pore

Abstract: The influences of the boundary effect and the charged conditions of a particle on its diffusiophoretic behavior are studied by considering the diffusiophoresis of a nonuniformly charged sphere along the axis of a narrow cylindrical pore. We show that the surface charge distribution of the particle is capable of yielding the complicated phenomenon of double-layer polarization and, together with the presence of the pore, leads to profound and interesting diffusiophoretic behaviors. For example, if the electrophoresis effect coming from the difference in the ionic diffusivities is absent, then the diffusiophoretic velocity of a particle with the sign of the surface charge on its middle part different from that on its left- and right-hand parts has both a local maximum and a local minimum as the fraction of the middle varies; that velocity has only a local minimum if the whole particle is charged with the same sign. If the electrophoresis effect is significant, then the diffusiophoretic behavior of the particle depends mainly on its averaged surface charge density.