(375g) Interaction of a Phoretic Microbubble with a Solid Wall

Marangoni self-propulsion of small droplets or bubbles arises when a gradient of surface tension on their interface —due to either a gradient of temperature or chemical composition— induces a flow tangential to the interface that drives the particle towards the opposite direction. This phenomenon is relevant to important processes in both nature and technology, ranging from propulsion of microorganisms, transport in microfluidic devices and collective dynamics in active matter systems. The study of phoretic self-propulsion has received considerable attention during the last few decades, and the literature about this area of research is extensive.

In a recent study we examined numerically the Marangoni self-propulsion of a microbubble immersed in an unbounded viscous liquid, arising after a sector of its interface becomes contaminated with a surfactant. The main result of that study is that the swimming distance is proportional to the fraction of the bubble interface initially clean.

In this work we extend our previous study by examining the interaction of the self-propelling microbubble with a solid wall, towards which the bubble heads on. The study is motivated in cleaning applications and the removal of biofilms by means of microbubbles laden flows, with potential environmental benefits.

The study was carried out by solving numerically the Navier-Stokes and mass conservation equations that describe the transport of momentum and surfactant on the liquid surrounding the freely deforming bubble and on its interface.

Our results show that the flow created around the Marangoni self-propelling bubble during its impact on the solid wall produces shear stresses whose magnitude is large enough to remove several types of microorganisms from the surface, as quantified by other authors, and may therefore contribute to the cleaning of fouled surfaces. These effects, however, depend strongly on the initial separation between the bubble and the solid surface.