Effects of Rotary Brownian Motion in Rheological Transients of Suspensions of Spheroids

The rheological transients in simple shear flow of a dilute, initially isotropic suspension of monodisperse spheroids having strong rotary Brownian motion are considered theoretically. The principal rheological properties of an initially isotropic suspension are calculated from the principal stresses and show changes due to the Brownian diffusion. The intrinsic normal stress difference $ξ31$ in the direction of flow starts from zero, increasing initially until a steady state is reached asymptotically. Similar behavior is shown by the intrinsic viscosity η, except for the initial nonzero value. On the other hand, the intrinsic normal stress difference $ξ21$ in the direction normal to the flow increases from zero to pass through a maximum and then decays until it reaches an asymptotic negative value. The significance of these predictions is discussed briefly.