Effect of the driving pressure on the rate of thinning of microscopic foam films

The effect of the driving pressure on the rate of thinning of microscopic foam films from aqueous solutions of nonionic [C-12(EO)(8)] and anionic [DDBS] surfactants was studied experimentally. At the ionic strengths of the solutions used (0.024 or 0.1 mol l(-1)) the driving pressure was mainly governed by the capillary pressure, while the disjoining pressure was negligible, especially at a large film thickness. The studied films were obtained in glass cells of different radii (R-c) of the holder in which the film was formed. The values of the drainage constants ratios (alpha(2)/alpha(1),), experimentally obtained for films under different experimental conditions were compared to the theoretically calculated ratios of the thinning rates (V-2/V-1). The deviations from the classical Reynolds law, obtained experimentally, correspond to the dependence of the rate of thinning on driving pressure required by the theoretical approach of Manev-Tsekov-Radoev. The results confirm the conclusions of the approach, accounting for the effect of the film thickness non-homogeneity on the rate of thinning. (C) 2003 Elsevier B.V. All rights reserved.