Memory impairment in flowing suspensions. I. Some theoretical considerations

When a suspension of nearly monodisperse rigid axisymmetric particles in a Newtonian liquid is sheared, the orientation distributions of the particle undergo damped oscillations of frequency twice that of the rotating particles. If the flow is stopped and then reversed, the oscillations regrow under certain restricted conditions until the initial state is fully restored: the system has perfect memory. Removing some of the restrictions causes imperfect recovery of the initial orientation distribution, so that when the flow is reversed cyclically back and forth, the orientation distribution eventually becomes time-independent: the system has lost all of its memory. A number of sources of memory impairment are considered theoretically, several of which are amenable to experimental verification and are illustrated by numerical calculation.