Effect of Microtextured Surface Topography on the Wetting Behavior of Eutectic Gallium-Indium Alloys

Liquid-embedded elastomer electronics have recently attracted much attention as key elements of highly deformable and "soft" electromechanical systems. Many of these fluid-elastomer composites utilize liquid metal alloys because of their high conductivities and inherent compliance. Understanding how these alloys interface with surfaces of various composition and texture is critical to the development of parallel processing technology, which is needed to create more complex and low-cost systems. In this work, we explore the wetting behaviors between droplets of gallium-indium alloys and thin metal films, with an emphasis on tin and indium substrates. We find that metallic droplets reactively wet thin metal foils, but the wettability of the foils may be tuned by the surface texture (produced by sputtering). The effects of both composition and texture of the substrate on wetting dynamics are quantified by measuring contact angle and droplet contact diameter as a function of time. Finally, we apply the Cassie-Baxter model to the sputtered and native substrates to gain insight into the behavior of liquid metals and the role of the oxide formation during interfacial processes.