Determination of the dynamic electrophoretic mobility of a spherical colloidal particle through a novel numerical solution of the electrokinetic equations.

The standard equations developed to describe the electrophoretic motion of a charged particle immersed in an electrolyte subjected to an oscillating electric field are solved numerically with a new technique suitable for stiff systems. The focus of this work is to use this solution to determine the dynamic particle mobility, one of several quantities that can be extracted from these equations. This solution is valid from low frequencies to indefinitely high frequencies and has no restriction on zeta potential, double-layer thickness, or electrolyte composition. The solution has been used to calculate the dynamic electrophoretic mobility of a particle for a wide range of double-layer thicknesses and zeta potentials. The solution agrees with analytic approximations obtained previously by other authors under the conditions of a thin double layer and low zeta potential. The results are also consistent with calculations valid at frequencies where the ion diffusion length extends a significant distance beyond the double layer as obtained by another numerical technique.

Calculation of the dynamic impedance of the double layer on a planar electrode by the theory of electrokinetics.

Applications of microelectromechanical systems in the biotechnological arena (bioMEMS) are a subject of great current interest. Accurate calculation of electric field distribution in these devices is essential to the understanding and design of processes such as dielectrophoresis and AC electroosmosis that drive MEMS-based devices. In this paper, we present the calculation of the electrical double-layer impedance (Z(el)) of an ideally polarizable plane electrode using the standard model of colloidal electrokinetics. The frequency variation of the electrical potential drop across the double layer above a planar electrode in a general electrolyte solution is discussed as a function of the electrode zeta potential zeta, the Debye length kappa(-1), the electrolyte composition and the bulk region thickness L.

Calculation of the electric polarizability of a charged spherical dielectric particle by the theory of colloidal electrokinetics.

Dielectrophoresis (DEP) is increasingly being explored as a means to manipulate or separate colloidal particles. The direction and strength of the DEP force depend strongly on the induced dipole strength, K, of a polarized particle, and predictions of DEP forces require carefully computed values for K. In this paper, we present the calculation of the dipole strength using the full electrokinetic theory of Mangelsdorf and White for both static and oscillating electric fields. The effects of particle zeta potential, radius, Debye length and electrolyte composition on the magnitude and sign of Re(K) are discussed. The full theory model is compared with the extended Maxwell-Wagner (EMW) model and the results show that the EMW model can fail to predict the full Re(K) variation with frequency, even predicting Re(K) with the incorrect sign depending on system parameters. A program for the dipole strength calculation shown in this paper is available from the authors.