Influence of adsorption kinetics and bubble motion on stability of the foam films formed at n-octanol, n-hexanol and n-butanol solution surface

Abstract

Lifetimes of single bubbles at surface of n-octanol solutions of various concentrations were determined for two different locations of the surface in respect to the capillary orifice at which the bubbles were formed. It was found that when solution surface was located ‘far’ ( L=39.5 cm) the average lifetimes of bubbles were shorter than that ones at the solution surface located ‘close’ ( L=4 cm) to the point of the bubbles formation. The bubble departing from the capillary orifice has the adsorption coverage determined by the mutual ratio of velocity of its formation and kinetics of surfactant adsorption. The degree of surfactant coverage over the surface of the growing bubble was calculated assuming that the surfactant adsorption at the surface of the departing bubble is governed by convective–diffusion. It was demonstrated that for the time of bubble growth t growth=0.16 s encountered in our experiments the departing bubbles had practically equilibrium coverage's in n-butanol and n-hexanol solutions, while in n-octanol solutions the adsorption coverage was much smaller than the equilibrium one. Thus, unlike for shorter chain n-alkanols, even for the location ‘close’ the partially non-symmetrical film is formed when in n-octanol solutions the bubble arrives at the free solution surface. For the location ‘far’, the bubble motion through the solution causes further disequilibration of the surfactant coverage over its surface. The bubble reaches the solution surface with its upstream pole practically devoid of surfactant and the fully non-symmetrical film is formed. Such fully non-symmetrical film is less stable than the film formed at the location ‘close’. Our results show that the lifetime of the foam film formed by a single bubble arriving at the solution surface strongly depends on ‘history’ of the bubble formation and motion.