Electroviscous effects in dispersions of monodisperse polystyrene latices

Abstract

Abstract The contribution of electroviscous effects to the viscosity of monodisperse polystyrene latices has been studied. The sols were prepared by emulsion polymerization using as emulsifier a weak acid soap and a strong acid soap, respectively. Particle sizes were determined by electron microscopy and turbidimetry. Excellent agreement between the two methods was obtained. Zeta potentials and charges of the electrokinetic unit were deduced from electrophoretic mobility measurements at different ionic strengths. The validity of the Einstein equation was demonstrated for perfectly stable latices when the primary electroviscous effect can be considered as negligible. Influences of ζ potential, particle charge, ionic strength, particle size, and rate of shear on the first- and second-order electroviscous effects have been investigated. For the primary electroviscous effect, a good agreement with the Booth Street's equation yielded too low viscosities, values predicted by the recent treatment of Chan, Blachford, and Goring were too high. However, this last theory represents a more realistic approach than the Street one.