Foam rheology in the wet and dry limits

Abstract

Understanding the rheological behavior of wet foams is important as a basic problem in fluid physics, and as a practical problem in many industries. This lecture will describe research into the wet and dry limits of foam rheology by a relatively new experimental technique in which foam drops are acoustically levitated and driven into motion. In the dry limit, the drops behave as viscoelastic solids. The effective moduli of the foam are estimated by observing the resonances of the drops and matching them to an analytical model for viscoelastic sphere vibrations. Analytical explorations of the wet limit have proceeded by considering the dynamics of a single bubble in a volume of liquid determined by the foam’s void fraction. The linearized result is a wave equation, from which the natural frequencies and mode shapes of wet foam drops are determined. Relationships between this wave equation and those of classical effective medium theories will be described. [Work supported by NASA.]