Influence of non-ionic adsorbing substances on the anomalous Kerr effect of hectorite dispersions

Abstract

There is a long tradition in investigating colloidal systems by transient electric birefringence. One interesting phenomenon is the observation of an anomalous signal in the semi-dilute concentration regime of charged colloidal dispersions. The occurrence of the anomalous Kerr effect is experimentally well documented but only poorly understood theoretically. Some years ago we investigated the influence of the block copolymer F127 on the anomalous Kerr effect in dispersions of the synthetic clay mineral saponite. The adsorption of F127 led to a disappearing of the anomaly. In this study we expanded the investigation to other systems. We carried out experiments with the synthetic clay mineral hectorite and three different adsorbing substances: the non-ionic surfactant C₁₂EO₉, the block copolymer F127 and the polymer polyvinylpyrrolidone. There seems to be a general rule that the adsorption of non-ionic substances reduces the anomaly. Additional measurements of electric conductivity, surface tension and electrophoretic mobility are presented to clarify this general observation.