The Electric Conductivity of Dilute Suspensions of Charged Porous Spheres
The effective electric conductivity of a dilute suspension of polyelectrolyte molecules or charged flocs in an electrolyte solution is analytically studied. The model used for the particles is a porous sphere in which the density of hydrodynamic frictional segments, and therefore also that of the fixed charges, is constant. The equations which govern the electrochemical potential distributions of ionic species and the fluid flow field inside and outside a porous particle migrating in an unbounded solution are linearized assuming that the system is only slightly distorted from equilibrium. Using a perturbation method, these linearized equations are solved for a porous sphere in a uniform applied electric field with the density of the fixed charges as the small perturbation parameter. An analytical expression for the effective conductivity of a dilute suspension of identical charged porous spheres is obtained from the average electric current density calculated using the solution of electrochemical potential distributions of the ions. The result demonstrates that the presence of the fixed charges in the porous particles can lead to an augmented or a diminished electric conductivity of the suspension relative to that of a corresponding suspension of uncharged porous particles, depending on the characteristics of the electrolyte solution and the suspending particles. When the anionic and cationic diffusion coefficients of a symmetric electrolyte are the same, the correction for the effect of the fixed charges of the particles on the electric conductivity of the suspension is proportional to the square of the fixed charge density. Copyright 1997Academic Press
Liu
YC
Department of Chemical Engineering, National Taiwan University, Taipei, Taiwan, 106-17, Republic of China
Keh
HJ