The impact and bounce of air bubbles at a flat fluid interface

Abstract

The rise and impact of bubbles at an initially flat but deformable liquid-air interface in ultraclean liquid systems are modelled by taking into account the buoyancy force, hydrodynamic drag, inertial added mass effect and drainage of the thin film between the bubble and the interface. The bubble-surface interaction is analyzed using lubrication theory that allows for both bubble and surface deformation under a balance of normal stresses and surface tension as well as the long-range nature of deformation along the interface. The quantitative result for collision and bounce is sensitive to the impact velocity of the rising bubble. This velocity is controlled by the combined effects of interfacial tension via the Young-Laplace equation and hydrodynamic stress on the surface, which determine the deformation of the bubble. The drag force that arises from the hydrodynamic stress in turn depends on the hydrodynamic boundary conditions on the bubble surface and its shape. These interrelated factors are accounted for in a consistent manner. The model can predict the rise velocity and shape of millimeter-size bubbles in ultra-clean water, in two silicone oils of different densities and viscosities and in ethanol without any adjustable parameters. The collision and bounce of such bubbles with a flat water/air, silicone oil/air and ethanol/air interface can then be predicted with excellent agreement when compared to experimental observations.

Regimes of wettability-dependent and wettability-independent bouncing of a drop on a solid surface

“…In the latter case, the free surface deforms as the bubble approaches it and eventually ruptures concentrically at a certain radial location. Manica, Klaseboer & Chan (2016) show that the shape of the free surface can be described in the outer, i.e. , and inner, , regions separately.…”

“…By matching the two regions, Manica et al. (2016) obtain a simple expression for the radius of rupture of the bubble impacting a free surface, given by where is the radius of the bubble and is the force of impact.…”

“…In Manica et al (2016), is the buoyancy force of the rising bubble. But in the current study can be taken to be the impact force of a freely falling drop given by where is the time scale obtained by balancing inertia and surface tension forces, , and is the time taken by the drop to spread on the surface.…”

Coalescence Dynamics of Mobile and Immobile Fluid Interfaces

“…19,20 In other experiments when a mobile interface bubble rises toward the free water surface the bubble bounce and coalescence kinetics indicate that even in the case of ultrapure water, the free water surface appears to be immobile, probably due to contamination that originated from the laboratory atmosphere, and similar results have also been obtained with other polar liquids as ethanol. 21 From an experimental perspective, comprehensive explorations of the effects of varying surface mobility using well characterized and reproducible systems that allow quantitative comparisons are still lacking. Coalescence studies involving bubbles as well as hydrocarbon and 6 fluorocarbon droplets in water, all below the 100 µm size range, have been conducted using the atomic force microscope (AFM).…”

Recent Progress in Fabricating Superaerophobic and Superaerophilic Surfaces

“…On the other hand, an air bubble approaching a smooth solid surface under submerged condition experiences a hydrodynamic repulsive force originating from the drainage of liquid film beneath the air bubble . The physics behind the conduct of bubble could be deciphered based on the Reynolds lubrication theory and augmented Young–Laplace equation, details of the theoretical model can be found elsewhere . Reynolds lubrication theory illustrates the drainage dynamics of thin liquid film confined between a solid and an air bubble in a liquid medium.…”