EFFECT OF PARTICLE-SIZE DISTRIBUTION AND AGGREGATION ON ELECTROACOUSTIC MEASUREMENTS OF ZETA POTENTIAL

The electroacoustic procedure allows one to estimate the high-frequency mobility of colloidal particles in moderately concentrated suspensions. From the mobility it is possible to calculate the electrokinetic (zeta) potential, provided one can estimate the appropriate particle size for the kinetic units in the system. We show that the mass average particle size, determined from light scattering, is the measure that best estimates the size of the kinetic units for the electroacoustic method, even when the system is undergoing coagulation. A comparison is also made between the mobility formulas of O'Brien and of Babchin. The former is found to give much better agreement with zeta-potential measurements obtained on dilute suspensions of the same system. A more recent formulation by Babchin is in better agreement but neglects the permittivity of the particles.