Marangoni instability of a drop in a stably stratified liquid

TL;DR

This paper uncovers a new oscillatory Marangoni instability in drops within stably stratified liquids, revealing how stratification influences interfacial phenomena and is amplified in confined spaces.

Contribution

It introduces the first experimental and theoretical analysis of stratification effects on Marangoni instability, highlighting a new oscillatory behavior and its amplification in confined geometries.

Findings

Discovered a new oscillatory solutal Marangoni instability triggered by stratification.

Identified the critical stratification level for instability onset.

Showed stratification effects are amplified in confined geometries.

Abstract

Marangoni instabilities can emerge when a liquid interface is subjected to a concentration or temperature gradient. It is generally believed that for these instabilities bulk effects like buoyancy are negligible as compared to interfacial forces, especially on small scales. Consequently, the effect of a stable stratification on the Marangoni instability has hitherto been ignored. Here we report, for an immiscible drop immersed in a stably stratified ethanol-water mixture, a new type of oscillatory solutal Marangoni instability which is triggered once the stratification has reached a critical value. We experimentally explore the parameter space spanned by the stratification strength and the drop size and theoretically explain the observed crossover from levitating to bouncing by balancing the advection and diffusion around the drop. Finally, the effect of the stable stratification on the Marangoni instability is surprisingly amplified in confined geometries, leading to an earlier onset.