LOW-FREQUENCY DIELECTRIC RESPONSE OF POLYSTYRENE LATEX DISPERSIONS

The low-frequency permittivity and the conductivity increments of a we ll-characterized polystyrene sulfate latex with constant surface charg e density were measured in KCl electrolyte solutions. The ionic streng th was varied in the range 0.4-6 mM. The data could be explained with one absolute surface-conductivity parameter over the complete concentr ation range. The titratable surface charge density correlates well wit h the surface conductivity, the ions in the double layer having the bu lk mobility. The results are in good agreement with static conductivit ies of plugs composed of the same particles obtained in a previous stu dy (1). The electrokinetic charge obtained from streaming potentials ( 1) in that study is significantly lower, confirming the presence of co nduction behind the shear plane. In order to interpret the conductivit y data, simple analytical expressions have been derived for the freque ncy-dependent complex conductivity of a dilute dispersion of spherical particles with relatively thin double layers (kappa a much greater th an 1, where a is the particle radius and kappa(-1) the Debye screening length). The expressions are restricted to binary suspending electrol ytes. However, no restrictions on the ion mobilities and ion valencies are made. Our results agree well with the numerical results of the di electric model of Mangelsdorf and White (2, 3) and reduce to O'Brien's static conductivity results (4) in the limit of low frequencies. (C) 1998 Academic Press.