Birefringence of Solutions of Rigid Particles in Steady and Oscillatory Flow

Abstract

Theories of flow birefringence in steady and oscillatory shear flow for spheroidal particles are compared. It is shown, that proper normalization of birefringence functions make them identical for both flows at low gradients and frequencies. The deviations at high gradients and frequencies increase with increasing particle axial ratio. The theory for polydisperse particles is developed. From the limiting behavior at low and high gradients and frequencies it is possible to find various averages of the relaxation times of the particles and hence some description of the polydispersity. The differences between steady and oscillatory flow behavior for a monodisperse system persist even for the polydisperse case thus giving the possibility of indirectly checking some aspects of the monodisperse theory. Experiments on microcrystalline alumina (Baymal), tobacco mosaic virus, and bentonite are in essential agreement with theoretical predictions.