Tailoring Liquid Metal Interfaces: From Fundamental Surface Mechanics to Advanced Thermal Applications

Gallium-based liquid metals such as eutectic Ga–In (EGaIn) combine metallic thermal/electrical conductivity with room-temperature fluidity and low vapor pressure, making them attractive for soft electronics and thermal interface materials. However, their native gallium oxide skin creates complex wetting behavior, large contact-angle hysteresis, and leakage/pump-out issues that limit practical use. This presentation discusses an interface-centered framework for understanding and engineering liquid metals. We first revisit the distinction between surface energy and surface stress in oxide-coated liquid metals and propose a modified Young’s equation that accounts for both the oxide surface energy and the strain-dependent mechanical tension of the skin. This model rationalizes the large but substrate-sensitive advancing contact angles of liquid metals, the role of adhesion work at the three-phase contact line, and the collapse of oxide “sacs” during receding. Building on this mechanistic understanding, we then present strategies for advanced thermal interface materials based on liquid-metal composites. Interface-control additives and plasma-assisted mechanochemistry are used to reduce interfacial energy between liquid metals and ceramic fillers such as Al₂O₃ and AlN, enabling spontaneous composite formation, improved wetting/adhesion, reduced internal thermal resistance, and leakage-free paste-like behavior. The resulting composites achieve high thermal conductivities of approximately 30 W m⁻¹ K⁻¹ for liquid metal/Al₂O₃ systems and up to ~110 W m⁻¹ K⁻¹ for plasma-assisted AlN composites, while maintaining conformal contact and mechanical stability. These results highlight liquid-metal interface tailoring as a route to bridge fundamental surface mechanics and scalable thermal management for high-power electronics.