Effect of impurities in water on the drainage of the liquid film formed between a mica plate and a bubble

Abstract

The drainage and rupture of the thin liquid film formed between a flat mica plate and an approaching bubble with a constant velocity have been investigated experimentally. The effect of impurities in water on the drainage and rupture of the liquid film has also been evaluated by the comparison of the solutions: ultrapure water, two electrolyte solutions (0.05 M MgSO₄ solution and 0.05 M CH₃COONa solution) and surfactant solution (10 ppm Triton X-100 solution). The approaching velocity of a bubble toward a mica plate was controlled in the range from 1 μm/s to 1000 μm/s and the development of the relative thickness distribution of a thin liquid film was measured with the interferometer and the high-speed observation. As a bubble approaches toward the mica surface, the film shape changes from pimple to dimple, and the depth of dimple does not change during the dimple formation and the rim of the dimple spread wider. By the increase of approaching velocity, the depth of dimple tends to be deeper. By the comparison of 0.05 M MgSO₄ solution, 0.05 M CH₃COONa solution and ultrapure water, the dimple formations until the thinnest film thickness at the rim of the dimple becomes less than the limit of the thickness measurement of about 100 nm are similar. On the other hand, the timing of rupture retards in the electrolyte solutions, and its tendency is qualitatively consistent with the intensity of the effect of the bubble coalescence inhibition. The film with a thickness of less than about 100 nm becomes more stable when we used the mica plate as a solid surface and the rupture timing remarkably retards comparing with the case of a glass plate.