Worm-like instability of a vibrated sessile drop

TL;DR

This paper investigates how vertical vibrations induce a worm-like shape instability in a low surface tension droplet, revealing the role of Faraday waves in controlling the droplet's deformation.

Contribution

It demonstrates a simpler system where Faraday waves cause shape instability without involving contact line oscillations, and provides a theoretical model linking wave amplitude to droplet elongation.

Findings

Faraday waves control droplet shape during vibration.

A phase diagram of the instability was systematically mapped.

The theoretical model matches experimental measurements.

Abstract

We study the effects of vertical sinusoidal vibrations on a liquid droplet with a low surface tension (ethanol) deposited on a solid substrate. In a precise range of amplitudes and frequencies, the drop exhibits a dramatic worm-like shape instability with a strong symmetry breaking, comparable to the one observed by Pucci et al. (Phys. Rev. Lett., 106 (2011) 024503) on a vibrated floating lens. However, the geometry of our system is much simpler since it does not involve the oscillation and deformation of a liquid-liquid-air contact line. We show that the Faraday waves appearing on the surface of the droplet control its shape and we draw a systematic phase diagram of the instability. A simple theoretical model allows us to derive a relation between the elongation of the droplet and the amplitude of the Faraday wave, in good agreement with measurements of both quantities.