Elucidating the oscillation instability of sessile drops triggered by surface acoustic waves

TL;DR

This paper investigates the oscillation instability in sessile drops caused by surface acoustic waves, combining experimental observations with a novel optomechanics-inspired model to explain the complex interplay of hydrodynamics, acoustics, and capillarity.

Contribution

It introduces a new model inspired by optomechanics that explains the instability mechanism in SAW-driven sessile drops, supported by high-speed imaging and pressure measurements.

Findings

Deciphered the physics of oscillation instability in sessile drops.

Developed a coupled model linking acoustic modes and surface deformation.

Provided experimental validation of the proposed mechanism.

Abstract

The oscillation instability of sessile drops is ubiquitous in surface acoustic wave (SAW)-powered digital microfluidics. Yet, the physics underlying these phenomena has not been elucidated owing to the interplay between hydrodynamics, acoustics and capillarity. We decipher the instability by combining high-speed imaging with pressure measurements. We rationalize the observed behaviour with a model inspired from optomechanics, which couples an intracavity acoustic mode excited by the SAW to a surface deformation eigenmode through amplitude modulation and delayed radiation pressure feedback.