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JP Hsu

Publications and source records attributed to JP Hsu.

13 recordsLinked to original sources
PubMed2000

Electroosmotic Flow of a General Electrolyte Solution through a Fibrous Medium.

The electroosmotic flow of a general electrolyte solution through a fibrous medium is modeled theoretically taking the effect of double-layer polarization into account. The result obtained is applicable to an arbitrary level of electrical potential. We show that if the effect of double-layer polarization is neglected using the linearized Poisson-Boltzmann equation will underestimate electroosmotic velocity. The deviation becomes inappreciable, however, if kappaa is either very large or very small, kappa and a being, respectively, the reciprocal Debye length and the radius of a fiber. If the surface potential is high, the variation of electroosmotic velocity as a function of kappaa may exhibit a local maximum and a local minimum, and the larger the porosity of the fibrous medium the lower the level of surface potential for the local extremals to occur. If kappaa is small, the effect of surface potential on the electroosmotic velocity is more significant than that of double-layer polarization, and the reverse is true if kappaa is large. Copyright 2000 Academic Press.

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PubMed1999

Electrical Interaction Energy between Two Charged Entities in an Electrolyte Solution.

The electrical interaction energy between two charged entities in an electrolyte solution plays a significant role in various phenomena in colloid and interface science. Available methods for the estimation of this energy under the Debye-Huckel condition are discussed briefly, and a systematic approach based on a boundary integral method, which has the potential to yield an approximate analytical expression for various types of surfaces under a general surface condition, is introduced. The linear sizes of the interacting entities can be comparable or one is much larger than the other. A typical example for the former includes, for instance, the interaction between two colloidal particles. The stability behavior of a colloidal dispersion belongs to this category. That for the latter includes the interaction between a particle and a wall. The adsorption of particles to surfaces and the electrophoretic motion of particles near a boundary, for example, belong to this category. Extensions to more complicated cases, for example, multiple particles and arbitrary surfaces, are also discussed. Copyright 1999 Academic Press.

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PubMed1999

Electrophoretic Mobility of a Concentrated Suspension of Spherical Particles.

The electrophoretic behavior of concentrated spherical colloidal particles is analyzed theoretically for all levels of scaled surface potential &phi;a, taking the effect of double-layer polarization (DLP) into account. The result of numerical simulation reveals that for a very small kappaa (<0.01), kappa and a being, respectively, the reciprocal Debye length and the particle radius, or a very large kappaa (>100), using a linearized Poisson-Boltzmann equation (PBE) and neglecting the effect of DLP is reasonable; for an intermediate kappaa, appreciable deviation may result. The deviation is negative if kappaa is small, and positive if kappaa is large. The mobility against kappaa curve may have a local minimum and a local maximum. If &phi;a is low, the mobility increases with the porosity of the system under consideration, and for a fixed porosity, the mobility increases with kappaa. If &phi;a is high and kappaa is small, the effect of &phi;a (i.e., solving a nonlinear PBE) on the mobility of a particle is more significant than that of double-layer polarization, and the reverse is true if kappaa is large. For an intermediate kappaa, the effect of DLP is more significant than that of &phi;a when the porosity is high, and the reverse is true if it is low. Copyright 1999 Academic Press.

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PubMed1998

Electrophoretic Mobility of a Sphere in a Spherical Cavity.

The electrophoretic behavior of a spherical particle in a spherical cavity is analyzed theoretically, taking the effect of double layer polarization into account. We show that for the case where the particle is positively charged and the cavity uncharged if the surface potential of particle is high, the variation of the mobility of the particle as a function of kappaa has a minimum, kappa and a being respectively the reciprocal Debye length and particle radius. This minimum does not appear if the effect of double layer polarization is neglected. The variation of the mobility as a function of kappaa has a minimum for a medium value of lambda (= particle radius/cavity radius); it becomes negligible if lambda is either small or large. In the case where the particle is uncharged and the cavity positively charged, if the surface potential is high, the variation of mobility as a function of kappaa has a maximum; if it is low, the mobility increases monotonically with kappaa. Here, the mobility is mainly determined by the drag force, rather than by the electric force, acting on the particle as in the case where the particle is positively charged and the cavity uncharged. If both the particle and the cavity are charged, the electrophoretic behavior of the particle can be deduced from the results of the above two cases. Copyright 1998 Academic Press.

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PubMed1997

Electrophoretic Mobility of a Spherical Particle in a Spherical Cavity.

The electrophoretic mobility U of a spherical particle in a spherical cavity for the case of low electric field is estimated for an arbitrary thick electrical double layer. We show that if the particle is uncharged and the cavity negatively charged, the deviation in the mobility based on the linearized Poisson-Boltzmann equation, UL, can be serious even at a low electrical potential. In this case, the variation of the absolute deviation, |U - UL| as a function of kappaa, kappa and a being, respectively, the reciprocal Debye length and particle radius, has a maximum. The kappaa at which the maximal absolute deviation occurs increases with lambda (particle size/cavity size), and the maximal absolute deviation decreases with lambda. The latter increases with the absolute surface potential of cavity. If the particle is positively charged and the cavity uncharged, UL is sufficiently accurate if the electrical potential is low. Copyright 1997 Academic Press.

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PubMed1997

Dynamic Interactions of Two Electrical Double Layers

The unsteady-state electrical potential and the concentrations of ions between two identical, negatively-charged particles immersed in an a:b electrolyte solution are investigated. In particular, the effects of ionic strength, I, the geometric mean of the diffusivities of counterions Dcon and coions Dco, D, the separation distance between two particles, H, and the surface charge density, sigma0, on these distributions are examined. We conclude that under the following conditions a system needs a longer time for ions to reach equilibrium distributions: (a) small I, (b) small D, (c) large H, and (d) large sigma0. The rate of approach of two particles is faster if both surfaces are maintained at constant potential than if both surfaces are at constant charge density. The dynamic behavior of the relaxation of ions in the double layers has the effect of retarding the motion of particles. The deviation in the contact time between two particles predicted by an equilibrium model, which assumes that the distributions of ions in a double layer reach the Boltzmann distribution instantly, from that estimated by the corresponding dynamic model is on the order of 10%. Copyright 1997 Academic Press. Copyright 1997Academic Press

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PubMed1997

Electrostatic Potential Distribution for Spheroidal Surfaces in Symmetric Electrolyte Solutions

The electrostatic potential distribution for a charged spheroidal surface immersed in a symmetric electrolyte solution is derived. Such surfaces simulate a wide class of dispersed entities. Two types of boundary condition at the solid surface are considered, constant surface potential and constant amount of surface charges; both conductive and nonconductive surfaces are examined for the latter. The present analysis extends the conventional one-dimensional treatment on simple geometries to a two-dimensional space. A perturbation method is adopted to solve the governing Poisson-Boltzmann equation for the case of thin to moderately thick double layers. The classic results for planar and spherical surfaces can be recovered as special cases of the present analysis. The basic thermodynamic properties of the system under consideration, such as Helmholtz free energy, entropy, and surface excess, are derived. We show that using an equivalent sphere to approximate a spheroid can lead to an appreciable deviation in the prediction of the Helmholtz free energy. For a thin double layer, assuming a planar geometry will underestimate the Helmholtz free energy. Copyright 1997Academic Press

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PubMed1997

Electrostatic Interaction between Two Ion-Penetrable Charged Spheroids

The electrostatic interaction between two ion-penetrable, charged spheroidal particles is examined theoretically. These particles can assume different sizes and an arbitrary spatial orientation. The electrical potential distribution is derived analytically under the Debye-Huckle condition. The results for two interaction spheres, one spheroidal particle and a planar surface, and rigid particles covered by an ion-penetrable membrane can be recovered as the special cases of the present general problem. We show that, for a fixed center-to-center distance between two particles, regardless of their relative sizes, the interaction free energy is the greatest if their major axes lie on the same line (head-to-head), and the smallest if their major axes are perpendicular to each other but not on the same plane (perpendicular).

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PubMed1997

The Critical Coagulation Concentration of Counterions: Spherical Particles in Asymmetric Electrolyte Solutions

The ratio of the critical coagulation concentration (CCC) of counterions is evaluated for spherical particles and asymmetric electrolytes. A perturbation method is adopted to solve the Poisson-Boltzmann equation governing the electrical potential distribution of the system under consideration. On the basis of the result obtained, an approximate expression for the CCC is derived. Another approach based on the Derjaguin approximation is also used to estimate the CCC. We show that the CCC ratio of counterions is a complicated function of the valences of the ion species in the liquid phase and the sizes of particles. Depending upon the thickness of the Debye length, the CCC ratio of counterions for various combinations of electrolytes can be estimated. The classic Schulze-Hardy rule for planar particles in a symmetric electrolyte solution can be recovered as a limiting case of the present model. If the surface potential is low, the effect of curvature on the CCC ratio of counterions is negligible.

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PubMed1996

Electrical Potential Distribution for Multiple Charged Surfaces under a General Boundary Condition

The electrical potential distribution of a system containing multiple charged surfaces with a general boundary condition is investigated theoretically. Here, a surface can assume a constant potential/charge density, or an arbitrary combination of the two, i.e., a mixed boundary condition; the latter is of particular significance in practice. Typical example includes surfaces containing various ionizable functional groups, charge-regulated surfaces, dynamic surface conditions, and patchwise charged surfaces. A systematic iterative method is proposed for the resolution of the linearized Poisson-Boltzmann equation governing the electrical potential distribution of the system under consideration. The sufficient and necessary condition under which the method proposed is applicable is discussed. Since the coefficients in the expression for the boundary condition at surface can be an arbitrary function, the present problem is a generalized Robin problem. The conventional constant potential (Dirichlet) problem and constant surface charge (Neumann) problem can be recovered as special cases of the present model. A criterion is proposed to decide whether the separation distances between particles is appropriate for various approximate procedures, e.g., pairwise addition and linear superposition. We show that a system containing a large number of surfaces can be simulated by one which has relatively few surfaces.

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