Seminars

Soap froth – the quintessential foam – is composed of polyhedral gas bubbles separated by thin liquid soap films, but remarkably, this material exhibits elastic-plastic behavior. An elementary model based on 2D liquid honeycombs can explain the basic physics of this response (Princen, 1983) but random microstructures must be analyzed to reveal more realistic behavior. The cell-level response of random 2D and 3D foams has been explored through simulations with the Surface Evolver, a computer program developed by Ken Brakke – this is an exercise is the geometry of minimal surfaces. The calculations are in excellent agreement with the seminal experiments by Matzke (1946) on 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.