Ring-shaped structure in free surface flow of non-Newtonian liquids.

We report the formation of a ringlike structure in the flow of particular non-Newtonian liquids coating a rotating vertical disk. Experiments were performed with a known volume of the liquid and at varying rotation rates such that the inertial effects were negligible. The liquid injected on the rotating disk initially coats the surface uniformly, which then redistributes itself such that at steady state a significant amount collected into a circular ring, off center with the axis of rotation. Beyond a critical rotation speed and for a given liquid volume, the ring formation did not occur. The ring formation was not observed in the case of Newtonian liquids. Rheological measurements along with the shear rate calculations suggest that the shear thinning nature of the liquids could be responsible for the observed ring formation.