Effect of film size on drainage of foam and emulsion films

Abstract

AbstractAll available theoretical analyses for the drainage of thin plane‐parallel liquid films, such as those existing between two approaching liquid droplets or bubbles in the coalescence process, predict essentially the same dependence of rate of thinning of the intervening film on its size as is described by the Reynolds equation—that is, drainage time increases with the square of the film radius. Recently, we have reported experimental data for both foam and emulsion films which showed that the measured drainage times increase with about a 0.8 power of the film radius, a value much smaller than the theoretically predicted value of 2.0. Here we present a hydrodynamic analysis to predict the experimentally observed effect of film size on the kinetics of thinning of emulsion and foam films. We extend the applicability of the Reynolds model by accounting for the flow in the Plateau borders as well as the London‐van der Waals forces in the thin film phase. Our theoretical predictions are in good agreement with the experimental data on the dependence of drainage time of both foam and emulsion films on their radii.