Observations on the transient nature of shape-tilting bodies sedimenting in polymeric liquids

The terminal orientation of cylinders with flat ends, sedimenting in polymer solutions are seen to occur with their edges aligned with the direction of fall. This is referred to as shape-tilting in the literature. We show that for cylinders with aspect ratios L/d≠1, the shape-tilting phenomenon is in fact a transient phenomenon by extending our observation times to up to several hours when compared to a few minutes of observation time in previous experiments. Additionally, our experimental observations are confirmed by use of a simple analytical argument which invokes the symmetries of a Stokes flow and of the sedimenting body.