# Oxidation-Mediated Fingering in Liquid Metals

## TL;DR

This paper uncovers a new class of fingering instabilities in liquid metals caused by electrochemical oxidation, which drastically alters their shape and stability, with implications for reconfigurable devices.

## Contribution

It demonstrates how electrochemical oxidation can induce and control fingering instabilities in liquid metals, revealing a new universality class and the role of oxidative stresses.

## Key findings

- Oxidation lowers interfacial tension to near zero, causing shape changes.
- Fractal dimension of the instability is approximately 1.3.
- Oxidative stresses can halt instabilities at higher potentials.

## Abstract

We identify and characterize a new class of fingering instabilities in liquid metals; these instabilities are unexpected due to the large interfacial tension of metals. Electrochemical oxidation lowers the effective interfacial tension of a gallium-based liquid metal alloy to values approaching zero, thereby inducing drastic shape changes, including the formation of fractals. The measured fractal dimension ($D = 1.3 \pm 0.05$) places the instability in a different universality class than other fingering instabilities. By characterizing changes in morphology and dynamics as a function of droplet volume and applied electric potential, we identify the three main forces involved in this process: interfacial tension, gravity, and oxidative stress. Importantly, we find that electrochemical oxidation can generate compressive interfacial forces that oppose the tensile forces at a liquid interface. Thus, the surface oxide layer not only induces instabilities, but ultimately provides a physical barrier that halts the instabilities at larger positive potentials. Controlling the competition between surface tension and oxidative (compressive) stresses at the interface is important for the development of reconfigurable electronic, electromagnetic, and optical devices that take advantage of the metallic properties of liquid metals.