Nanometer-Resolved Collective Micromeniscus Oscillations through Optical Diffraction

TL;DR

This study investigates nanometer-scale collective oscillations of liquid-gas menisci on superhydrophobic surfaces using optical diffraction, revealing a resonance at hundreds of kHz driven by acoustic coupling.

Contribution

It introduces a real-time optical diffraction method to resolve nanometer-scale meniscus oscillations and models the collective resonance behavior with unsteady Stokes equations.

Findings

Resonance observed at a few hundred kHz depending on geometry

Nanometer-scale oscillations detected with sub-microsecond resolution

Collective acoustic mode explains the resonance frequency

Abstract

We study the dynamics of periodic arrays of micrometer-sized liquid-gas menisci formed at superhydrophobic surfaces immersed into water. By measuring the intensity of optical diffraction peaks in real time we are able to resolve nanometer scale oscillations of the menisci with sub-microsecond time resolution. Upon driving the system with an ultrasound field at variable frequency we observe a pronounced resonance at a few hundred kHz, depending on the exact geometry. Modeling the system using the unsteady Stokes equation, we find that this low resonance frequency is caused by a collective mode of the acoustically coupled oscillating menisci.