The approach of gas bubbles to a gas/liquid interface

Abstract

The approach of nitrogen bubbles to the free surface of aqueous glycerol solutions and polyglycol oils was investigated using interference rings and interference colors to estimate the thickness of the liquid films. The rate of approach in close proximity to the liquid surface was found to decrease rapidly with decreasing separation. The intervening liquid film deformed with progressive thinning and, eventually, was thinnest around a ring at a distance c′ from the center. Analysis showed that this occurred where the upper surface started to bulge. The rate of film thinning increased with decreasing film viscosity and showed good agreement with a theoretical equation previously derived. The rupture of the intervening liquid film occurred over a range of film thicknesses in any given system, in many cases at values <900 A. The effect of an added surfactant was to decrease the rate of film thinning at comparable thicknesses, increase the mean rest-time, and lead to thinner films at rupture than in the case of the pure system.