The particle charging behavior of ion-exchanged surfactants in apolar media

Abstract

This paper investigates the effects of surfactant counterion electronegativity on the micellization and particle charging behavior of a series of ion-exchanged surfactants in apolar media. The sodium cation in Aerosol OT (AOT) was exchanged for four divalent cations and one trivalent cation, resulting in five AOT analogs. The critical micelle concentrations (CMCs) of each of these AOT analogs was measured by conductometric techniques. For each surfactant, dispersions were made with three different mineral oxides, spanning a range of points of zero charge (PZC), and their electrophoretic mobilities were measured. It was found that all five surfactants behaved as acids, charging all particles positively, with zeta potentials up to 201mV. It was also found, generally, that as the electronegativity of the surfactant head-group increased, the imparted particle mobilities also increased. The trivalent AOT analog imparted higher mobilities than an electronegatively comparable divalent analog.