February 7, 2003 Colloquium

Rising bubbles in polymeric fluids evince some of the significant differences between polymer solutions and Newtonian fluids, including a sharp cusp at the trailing end of the bubble. In surfactant solutions of wormlike micelles, rising bubbles can additionally oscillate in shape and speed. The motion is roughly periodic, with no apparent damping effects, and does not reach a steady state.

Since micelles are subject to thermal as well as flow induced scission-recombination reactions, we have studied the dependence of these oscillations on both temperature and concentration. We find two disconnected regions of oscillation in this phase plane. Fixing concentration, we find temperature bounds for the oscillations and regions in which polymer-like behavior is recovered. Rheological tests were performed at different points in the phase plane to compare existence of the oscillations with the material properties of the fluids.