Influence of bubble surface fluidity on collision kinetics and attachment to hydrophobic solids

Influence of variations of the bubble surface fluidity on its rising velocity, kinetics of collisions, bouncing and attachment to hydrophobic solid surface was studied experimentally and modeled by means of numerical calculations. A theoretical model was elaborated to describe gradual retardation of the bubble surface fluidity as observed in surface-active substances solutions of increasing concentration. The model is described in details and validated against the experimental results. In experiments the ascending bubble collisions with solid wall, in surface-active substances solutions of gradually increasing concentration, were monitored using high speed photography, while in numerical simulations the bubble behavior (rising velocity, shape deformations, spatial displacement during collisions and bouncing) was determined by solving the governing equations describing conservation of momentum and mass of an incompressible viscous liquid. The results obtained in experiments and in numerical simulations were in a good agreement. Therefore, the model elaborated was used also to confirm that air presence at hydrophobic solid surfaces is responsible for the reported earlier effect of prolongation of time of the bubble attachment at higher concentrations of surface-active substances. The results of numerical simulations showed similar trends as the experimental data, that is, with increasing degree of the bubble surface immobilization the calculated values of the bubble attachment time were prolonged.