Physics Colloquium
Friday, Sept. 15th, 2006,
4:00 P.M.

E300 Math/Science Center; Refreshments at 3:30 P.M. in Room E200

Andrew Kraynik
Sandia National Laboratory

Foam structure and rheology: the shape and feel of soap froth

Soap froth-the quintessential foam-is composed of polyhedral gas bubbles separated by thin liquid films. Why do foams have a shear modulus and yield stress, which we usually associate with solids? How are the bubbles shaped and how do they pack? These and other questions have been explored through simulations with the Surface Evolver, a computer program developed by Brakke. The calculations are in excellent agreement with seminal experiments by Matzke (1946) on the foam structure and shear modulus measurements by Princen and Kiss (1986). The connection between elastic-plastic rheology and foam structure involves intermittent cascades of topological transitions; this cell-neighbor switching is a fundamental mechanism of foam flow.

Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.