Electric Birefringence and Electrophoretic Light Scattering for Colloid Stability Characterisation*

The effect of an electric field on a dilute suspension of asymmetric colloidal particles is to impose rotational order which can be detected as an induced birefringence in the sol. Furthermore, · if the particles are charged, such rotation is followed by electrophoretic translation. In a single apparatus, pulsed electric fields have been applied to sols of the rod-like clay mineral attapulgite, and both the transient induced birefringence and the variation in the fluctuations of the scattered light have been measured. Experiments involving the addition of CTAB surfactant, resulted in the measurement of the electrical polarisability anisotropy, electrophoretic mobility, translatory and rotary diffusion coefficients as the inherent negative surface charge of the mineral particles was swept through the zero point of charge and into a positive condition. The accompanying changes in sol stability and flocculation were monitored in terms of these parameters.