Rheo-optical transients in sheared suspensions. Part 2.—Polydisperse spheroids

Abstract

Transient orientation-dependent properties of a flowing suspension of polydisperse spheroids are considered when oscillations in the particle orientation distribution are highly damped by rotational phase mixing. A convenient time scale for the behaviour of such systems is the most probable period of rotation, i.e. that value which corresponds to a maximum in the distribution of particle periods of rotation. In the case of oblate spheroids, for example, due to the nature of the dependence of the period of rotation on the particle axis ratio, the time-dependence of the transients favours periods larger than the period determined by the mean particle axis ratio. Rheo-optical transients in turbidity and angular scattering, together with their frequency spectra, which were obtained experimentally from polydisperse suspensions of kaolin undergoing simple shear flow, qualitatively confirm this behaviour.