(98ar) Structure Formation During Vibration of Viscoplastic Suspensions of Carbopol Microsponges

Complex fluids, including particulate suspensions, emulsions, granular media and Bingham fluids, exhibit a variety of interesting surface structures when subjected to vertical vibration.  Although several explanations for these phenomena have been proposed, there is currently no quantitative, accepted theory or model that explains them.  We have studied the behavior of gelled solutions filled with swollen, polymeric Carbopol “microsponges” neutralized with triethanolamine (TEA).  New, previously unreported features have been observed, including the spontaneous formation of holes at the corners of regular polygons.  The number of holes, and therefore the type of polygon observed, depend on the mass of fluid studied, as well as the components in the Carbopol solution.  Lubrication theory is used to obtain qualitative insights into the observed behavior.