Thermal interface materials (TIMs) improve thermal transport away from computer chips by filling micro air gaps between the rough surfaces of adjacent components (e.g., between the computer chip and heat spreader). TIMs typically consist of a polymer or grease with solid particle additives that have high thermal conductivity such as diamond, silver, aluminum nitride, etc. Despite these efforts, TIM conductivities are still usually below 2 W m^-1 K^-1 because the small point-like contacts between solid filler particles lead to large thermal contact resistances that bottleneck thermal transport.

I present my group’s ongoing work to use heterogeneous liquid metal (LM) particles to overcome thermal transport bottlenecks in polymer composites. The central premise behind this effort is that LM-coated particles will have enlarged particle-particle contact regions relative to the point-like contacts between non-coated particles. In effect, the LM functions as a thermally conductive “solder” between particles.

I first present our work on Cu particles coated in LM (eutectic Ga-In-Sn). Using these particles, we achieve effective thermal conductivities up to ~ 10 W m^-1 K^-1 under certain circumstances. This Cu-LM system also benefits from a room-temperature reaction between the Cu and LM. Cu-LM mixtures initially start as a slurry and can be processed accordingly. However, this slurry transforms into a conductive solid within a practical time frame (e.g., tens of minutes). During this process, Ga leaches out of the LM and reacts with the Cu to form CuGa₂. This also shifts the LM away from its eutectic Ga-In-Sn composition and the LM itself solidifies. In this sense, the LM can be viewed as a solder that is molten at room temperature, but then solidifies via chemical reaction (as opposed to freezing). Another important byproduct of this reaction is that it sequesters the Ga and prevents Ga-induced corrosion of neighboring components.

I next present our ongoing efforts to develop LM-coated Al and LM-coated W particles. These metals have low reduction potentials, which creates opportunities to transform their surface for LM-coatings via galvanic replacement reactions. Additionally, I present our modeling concepts for LM-coated heterogenous nanowires that can enable TIMs that are simultaneously thermally conductive and electrically insulating.