Pattern Formation - Current Interests

1. Fingering instabilities in spreading fluid films: The contact line at the front of a thin layer of fluid spreading on a substrate can become unstable to the formation of a pattern of equally spaced fingers. This instability results from a competition between surface tension and the force driving the spreading, and is easily seen in molten butter in a frying pan. Other examples include spin coating and flow of a fluid layer down an incline. We have studied the onset of the fingering instability and the growth of the fingers in both of these cases, using both Newtonian and non-Newtonian fluids. Currently we are investigating the effect of yield stress on this instability.


2. Rayleigh-Bénard convection in complex fluids: A thin layer of fluid heated from below will develop flow in a pattern of convective rolls or cells when the temperature difference across the layer becomes sufficiently large. In small fluid samples, the flow pattern is very simple, but in large samples it can be extremely complex. We have studied convection in Newtonian fluids and are now planning to look at flow patterns that develop in complex fluids, including yield-stress fluids and viscoelastic materials.