The growth, drainage and breakdown of foams

This paper examines the behaviour of growing and collapsing foams. In particular, it focuses on the drainage of the liquid, and thus the evolution of the liquid content, within the growing or collapsing foam. By assuming that the films fail when they are subjected to a pressure above a certain critical pressure, the collapse of the foam is modelled. The model predicts that the growing foam behaviour can be divided into two regimes: at low gas rates, the foams will asymptote towards an equilibrium height, while above a certain critical gas rate, the foams will continue to grow indefinitely. This behaviour was found experimentally as well. At the higher gas rates, there is a change in the slope of the foam height versus time plot, though with the exception of a transition region, this relationship remains a linear relationship one. The difference between these slopes can be used to estimate the pressure exerted on the films at the top surface of the foam. Since these bubbles are bursting, this is the critical pressure required to cause film failure within the foam. When compared to the stability of films in single film experiments, those in the foam, not unexpectedly, demonstrate lower stability. This is due to vibrations and other disturbances that are present within flowing foams.