MOTION OF THE FRONT BETWEEN THICK AND THIN-FILM - HYDRODYNAMIC THEORYAND EXPERIMENT WITH VERTICAL FOAM FILMS

The motion of the front between thick and thin foam film formed in a v ertical frame is studied both experimentally and theoretically. In the experiments we used sodium dodecyl sulfate solutions with added NaCl. The rate of motion of the front turns out to be constant for a given electrolyte concentration, Other important quantities that are measure d are the thickness of the black film and the jump of the film tension , when the front reaches the bottom meniscus. The rate of the front tu rns out to be proportional to the jump of the film tension irrespectiv e of the amount of added electrolyte. The theoretical model we develop ed allows quantitative interpretation of the experimental data. It is demonstrated that the motion of the front ''thick-thin'' film is accom panied with the formation of microscopic steady capillary waves in the transition zone. We show that the energy dissipation in the him is co ncentrated mainly into the latter part of the transition zone. The stu dy can be helpful for the understanding of the mechanism of the foam f ilms drainage as related to the stability of foams.