Dependence of contact angle of liquid phase eutectic gallium–indium with interfacial oxide layer on van der Waals attraction

Gallium-based liquid metals (GBLMs) have both high fluidity and electrical conductivity and have recently raised great hopes with the promise of realizing soft electronics. By soft electronics, we mean electronic components that can retain their function while being bent and elongated. However, a nanometer-thick oxide skin forms on the GBLM surface, causing atypical interfacial behaviors, and the underlying physics remains unclear. Here, we present the results of a combined experimental and theoretical investigation of the dependence of contact angle of liquid phase eutectic gallium–indium (EGaIn) with oxide skin on van der Waals attraction. Our experiments showed that when EGaIn has an oxide skin, only the static advancing contact angle, not the equilibrium and static receding contact angles, can be specified. We suggest a mathematical model that explains how the static advancing contact angle of EGaIn depends on van der Waals force and the tension exerted on the oxide skin, elucidating the physics that determines the contact angle of EGaIn with the oxide skin in microscopic analysis. Our study helps us to better understand the interface of GBLMs, providing new insight into microfabrication techniques for GBLMs.