Energy balance in viscous liquid containing a bubble: Rise due to buoyancy

On importance of external conditions and properties of the interacting phases in formation and stability of symmetrical and unsymmetrical liquid films

Importance of external conditions and properties of phases creating liquid films, in outcome of the air bubble collisions with liquid/air and liquid/solids interfaces in clean water and in liquid solutions, is critically reviewed. The review is focussed on initial stages of the liquid films formation by bubbles colliding with interfaces, as well as, on analysis of the most important factors responsible for the collision's outcome, that is, either the rapid bubble bouncing or formation of the symmetrical or unsymmetrical liquid films and their thinning to the critical rupture thicknesses. Data on formation of liquid films under dynamic conditions, both in pure liquids and solutions of electrolytes and various surface-active substances, are reviewed and importance of hydrodynamic boundary conditions at interacting interfaces for energy balance in the system is discussed. It is shown that the liquid films stability, which in stagnant systems are directly determined by properties of the liquid/gas and liquid/solid interfaces, can be quite different in dynamic environment. A mechanism of the bubble bouncing from various interfaces in terms of interplay between energy exchange and kinetics of liquid film drainage is analyzed. It is shown that this mechanism is universal and irrelevant on the nature of interacting phases. Moreover, mechanisms responsible for wetting (unsymmetrical) film stability under dynamic conditions are discussed in light of the most recent studies, showing a crucial role of electrolyte, kind and concentration of surface-active substances, electrical surface charge, hydrophilic/hydrophobic properties of solids and presence of air entrapped (nano- and/or micro-bubbles) at surfaces of highly hydrophobic solids in the liquid films rupture.