The kinetics of collision and bouncing of an air bubble on hydrophilic and hydrophobic solid surfaces immersed in distilled water is reported. We carried out the experiments and compared the bubble collision and bouncing courses on the stagnant and vibrating, with a controlled frequency and amplitude, solid/liquid interface. For stagnant interface differences in the outcome of the bubble collisions with hydrophilic and hydrophobic solid surfaces are resulting from different stability of the intervening liquid film formed between the colliding bubble and these surfaces. The liquid film was unstable at Teflon surface, where the three-phase contact (TPC) and the bubble attachment were observed, after dissipation of most of the kinetic energy associated with the bubble motion. For vibrated solid surface it was shown that kinetics of the bubble bouncing is independent on the hydrophilic/hydrophobic properties of the surface. Similarly like at water/glass hydrophilic interface, even at highly hydrophobic Teflon surface time of the bubble collisions and bouncing was prolonged almost indefinitely. This was due to the fact that the energy dissipated during the collision was re-supplied via interface vibrations with a properly adjusted acceleration. The analysis of the bubble deformation degree showed that this effect is related to a constant bubble deformation, which determined constant radius of the liquid film, large enough to prevent the draining liquid film from reaching the critical thickness of rupture at the moment of collision. The results obtained prove that mechanism of the bubble bouncing from various interfaces depends on interrelation between rates of two simultaneously going processes: (i) exchange between kinetic and surface energies of the system and (ii) drainage of the liquid film separating the interacting interfaces.
Financed by the National Centre for Research and Development under grant No. SP/I/1/77065/10 by the strategic scientific research and experimental development program:
SYNAT - “Interdisciplinary System for Interactive Scientific and Scientific-Technical Information”.