Electroacoustic studies of moderately concentrated colloidal suspensions

From electroacoustic theory it is now possible to determine the dynamic electrophoretic mobility of colloidal particles from measurements in any suspension for which the particle size is small compared to the sound wavelength (R. W. O'Brien, J. Fluid Mech., 1990, 212, 81); for dilute suspensions of spherical particles there is a simple formula for calculating the zeta potential from such mobility measurements (R. W. O'Brien, J. Fluid Mech., 1988, 190, 71). In this paper we present experimental verification of the theory for a latex and a cobalt phosphate sol, both of which are monodisperse, over a range of electrolyte concentrations and pH. We also present electroacoustic titration data on two polydisperse TiO2 sols, and discuss the discrepancies that result when these data are compared with the monodisperse theory.