Enhanced drainage and thinning of liquid films between bubbles and solids that support surface waves

Abstract

We study the thinning and drainage of the intermediate liquid film between a bubble and a solid surface at close proximity in the presence of a surface acoustic wave (SAW) in the solid. Specifically, we employ the diffraction of light to observe a long air bubble confined in a solid rectangular channel filled with silicone oil. This setup, constituting a two-dimensional physical model of thin film drainage, allows us to analyze the influence of a SAW on the rate of thinning of the micron-thick liquid film separating the bubble and the solid substrate. The viscous penetration of the SAW into the liquid imposes a convective drift of mass, redistributing the fluid in the film against capillary resistance and producing a net drift of liquid out of the film. The rate of drainage of liquid from the film increases by one to several orders of magnitude in comparison to the rate of drainage due to the Laplace pressure of the bubble alone. The experimental findings agree well with a newly developed theory describing the SAW-enhanced drainage as a competition between the capillary flow and SAW-induced streaming.

Revisiting the Electroacoustic Phenomenon in the Presence of Surface Acoustic Waves

“…The leakage of voltage from the solid surface and through the EDL under SAW excitation may explain electrokinetic effects observed near powered piezoelectric substrates. , Moreover, the partial discharge of an EDL under SAW excitation will alter the electrical properties of membranes . The corresponding reduction in ion concentration in the EDL reduces the osmotic pressure, which contributes to the stability of thin electrolyte films and is likely to alter the rate of attachment of particulates and molecules to the solid surface; the EDL repulsive or attractive pressure, experienced by particulates and molecules close to the solid surface, determines the rate of attachment …”

“…This insight indicates the good agreement between theory and experiment in studies on the contribution of SAW-induced drift flow to the dynamic wetting and deformation of thin aqueous films, where electrophoretic effects were ignored. 7,11 Moreover, under these circumstances, one may employ previous solutions for the SAW-induced flow field. 25 Further details are given in Appendix B.…”

“…It was lately demonstrated that surface acoustic waves (SAWs) are capable of manipulating and pumping liquids in nanochannels, , supporting dynamic wetting, − atomizing liquids, and manipulating the attachment of drops to SAW-actuated surfaces . In addition, SAWs were found to actuate submicron-thick electrolyte solutions for the analysis and manipulation of biochemical and biological agents, push water through membranes that comprise graphene nanochannels for eliminating nanometer-sized pollutants, and power paper-based microfluidics. − The unifying property in the above applications is the presence of SAWs near electrolyte solutions of nanometer and submicron length scales.…”

Active coating of a water drop by an oil film using a MHz-frequency surface acoustic wave

“…Millimeter-scale piezoelectric acoustic actuators of MHz-frequency surface acoustic waves (SAWs) have increased in popularity in previous years for manipulating micro to nano-liter liquids and particulates therein. [1][2][3][4] The actuators are piezoelectric substrates specifically designed to generate SAWs upon the application of a sinusoidal electrical signal, which supports electromechanical resonance in the substrate. The piezoelectric effect in the substrate of the actuator linearly transforms the electrical signal to a nanoscale oscillating mechanical vibration of maximum amplitude near the surface of the devices -SAW.…”

Acoustic flow in porous media

“…2015; Horesh et al. 2019), manipulating thin liquid films in confined mixtures (Horesh, Morozov & Manor 2017; Horesh, Zigelman & Manor 2020) and actuating submicron thick electrolyte solutions for the analysis and manipulation of biochemical and biological agents (Friend & Yeo 2011). Moreover, Ang et al.…”