Effect of motion on lifetime of bubbles at n-butanol solution surface

Abstract

A simple experimental technique was developed to measure lifetimes of single bubbles at an n-butanol solution surface located far and close to the point of bubble formation. It was found that when the free surface of the n-butanol solution was located far ( L=39.5 cm) from the point of bubble formation, the average lifetimes of bubbles were shorter than those of bubbles on the solution surface located close ( L=4 cm) to the point of bubble formation. According to theoretical predictions, the motion of a bubble through a surfactant solution leads to a non-uniform surfactant distribution over the bubble surface with substantially lowered adsorption coverage on its upstream part. When the solution surface was far, the distance travelled by the bubble was long enough for such a non-uniform distribution to develop and so a non-symmetrical foam film with its lower interface depleted of surfactant was formed at the solution surface. The stability of such a non-symmetrical film is lower than that of a symmetrical foam film formed by a bubble with equilibrium surface coverage undisturbed by motion. Therefore, lifetimes of bubbles were shorter at the n-butanol solution surface located far from the point of bubble formation. A good agreement was found between the lifetimes of bubbles and the lifetimes of foam films calculated from a simple theoretical model based on the velocity of thinning of the symmetrical and fully non-symmetrical foam film with one surface devoid of n-butanol molecules.