Enhanced wettability of gallium-based liquid metal alloys on copper films by promoting intermetallic reactions

Gallium-based liquid metal alloys (LMs) have promising prospects as circuit components for flexible electronics, while, their high surface tension is now challenging for wetting of LMs on polymer surfaces and further patterning. In this study, we prepared functional Cu thin films on PDMS to enhance wettability of EGaIn liquid metal, using metal reaction-enhanced wetting. By adjusting the deposition pressure for Cu film deposition and introducing silicon-bound PDMS, both surface characteristics and microstructures of the Cu films change greatly. The corresponding contact angle of EGaIn can be tuned from 19 degrees to 79.5 degrees. The folded texture of the Cu film surface reduces the actual contact area, leading to an increase in the contact angle. The higher I-(111)/I-(200) ratio in the Cu films improves the surface wettability, probably due to the fact that the (111)-phase orientation promotes the formation of CuGa2 reaction products. This tunable wettability of LMs is expected to improve the performance of flexible electronic devices.