THE ROLE OF SURFACE VISCOSITY IN GAS-DIFFUSION IN AQUEOUS FOAMS .1. THEORETICAL

Disproportionation is one of the processes that can determine foam stability. The rate of disproportionation is not only governed by differences in the Laplace pressure, topology of the bubble, or other well-known phenomena, but also by the gas composition and the rheological behavior of the bubble surface. The importance of surface rheological aspects such as surface viscosity is evident since the surface tension is one of the driving forces of this process. A new model is introduced describing the rate of gas diffusion in foams. In this model a power law is embodied describing the dependence of the surface viscosity on the relative surface compression or expansion rate. Also embodied in the model is the presence of gases with different solubility. The results show that the rate of disproportionation depends mainly on the partial pressure differences of the gases present. However, when gas composition throughout the foam is uniform the rheological behavior of the bubble surfaces is the main parameter determining the disproportionation rate. © 1990.