Bubble bouncing and stability of liquid films formed under dynamic and static conditions from n-octanol solutions

Abstract

Influence of n-octanol concentration on the bubble impact velocity, bouncing time and amplitude, the bubble coalescence time and stability of the liquid (foam) films formed under dynamic and static conditions was studied. Kinetics and outcome of the bubble collision with liquid–air interface were studied, for two different locations (L=3 and L=250mm) of the interface in respect to the point of the bubble formation (capillary orifice). Additionally, thickness and stability of microscopic foam films formed in n-octanol solutions were determined using microinterferometric method (Scheludko–Exerowa cell). It was found that for extremely low n-octanol concentration the bubble coalescence time (tc), was slightly shortened, due to diminishing of the bouncing amplitude. At higher concentrations, above a “threshold” value, the bubble coalescence time was prolonged significantly due to increased stability of the liquid film formed between “motionless” bubble and liquid–air interface. The tfilm values were used for evaluation of rupturing thicknesses of the liquid films formed under dynamic conditions. It was found that at low n-octanol concentrations the thicknesses of the rupturing films were of an order of a few μm. However, at higher n-octanol concentrations the foam films formed under dynamic conditions were stable enough to damp the disturbances caused by the colliding bubble. These films reached, before their rupture, the thicknesses below 100nm, that is, similar as the equilibrium thicknesses of the microscopic films.