On mechanism of the bubble bouncing from hydrophilic and hydrophobic solid surfaces

Abstract

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.

Experimental Study on the Interfacial Evolution of Taylor Bubble at Inception of an Annulus

“…It never reaches the critical thickness required for its rupturing and hence establishes a TCP. 36 Establishment of TCP would have caused rupturing of the Taylor bubble, which has not been observed during the experiments. Further, there was no retraction of the bubble after the collision phenomenon and only some interfacial waves were observed during the process.…”

Passage of a Taylor Bubble through a Stratified Liquid–Liquid Interface

“…The sudden change in δ* with time shows the retaining character of the bubble (Figure b). The retaining character of the film is due to the capillary pressure built into the film guided by the curvature of the Taylor bubble tip . The capillary pressure inside the entrapped water film will be built up after the achievement of the capillary length scale given by, .…”

“…It can be argued that with smaller mesh size than capillary length scale, hydrodynamic rupture will mimic physical rupture in the macroscale, 33 but to obtain microscale information during the physical rupture requires of multiscale simulation cannot be avoided. The flattening of the nose of the Taylor bubble occurs at the expense of its kinetic energy 34 in order to conserve its energy budget. Some part of the energy is dissipated due to the viscosity of the fluids which cannot be reclaimed back during its conversion from kinetic energy to the surface energy.…”

“…The retaining character of the film is due to the capillary pressure built into the film guided by the curvature of the Taylor bubble tip. 34 The capillary pressure inside the entrapped water film will be built up after the achievement of the capillary length scale given by, δ σ ρ ∼ g / crit . The dominant interfacial tension is between water and air having magnitude, σ w ∼ 0.072 N/m.…”

Recent Progress in Fabricating Superaerophobic and Superaerophilic Surfaces

“…In spite of the aforementioned situations wherein controlled air‐bubble adhesion is inevitable, compared to the fabrication of tailored water spreading substrates, less attention is paid to fabricate substrates that can control air bubble adhesion. Most of the reported studies focused on bubble nucleation, bubble–bubble interactions, bubble–solid interactions, bubble interactions in various surfactant solutions, spreading as well as bouncing effect of bubbles at various interfaces, and effect of hydrostatic pressure on microbubbles . The lack of propensity in research activity to control the bubble adhesion arises from the fact that, due to interfacial energy balance, superhydrophilic surfaces are inherently superaerophobic .…”