The Polymer Society of Korea

Abstract

Gallium-based liquid metals form oxide films a few nanometers thick in air, exhibiting interfacial behavior not fully explained by Young’s equation. We propose a modified equation incorporating the interfacial energies of the liquid metal–oxide and oxide–air interfaces and the oxide film’s mechanical tension. Each factor affecting the effective surface tension was separated and quantified using force balance and adhesion tests. By using a substrate of the same oxide film, the intrinsic interfacial energy and yield tension were measured independently for the first time. We show that the advancing contact angle of liquid metal on polymers is governed by the oxide film’s yield tension rather than the substrate’s surface energy, offering guidelines for liquid metal–polymer interface design. This analysis also provides a quantitative basis for why the advancing contact angle remains constant or dewetting occurs at these interfaces.