In Situ Alloying of Thermally Conductive Polymer Composites by Combining Liquid and Solid Metal Microadditives

Room-temperature liquid metals (LMs) are attractive candidates for thermal interface materials (TIMs) because of their moderately high thermal conductivity and liquid nature, which allow them to conform well to mating surfaces with little thermal resistance. However, gallium-based LMs may be of concern due to the gallium-driven degradation of many metal microelectronic components. We present a three-component composite with LM, copper (Cu) microparticles, and a polymer matrix, as a cheaper, noncorrosive solution. The solid copper particles alloy with the gallium in the LM, in situ and at room temperature, immobilizing the LM and eliminating any corrosion issues of nearby components. Investigation of the structure-property-process relationship of the three-component composites reveals that the method and degree of additive blending dramatically alter the resulting thermal transport properties. In particular, microdispersion of any combination of the LM and Cu additives results in a large number of interfaces and a thermal conductivity below 2 W m^-1 K^-1. In contrast, a shorter blending procedure of premixed LM and Cu particle colloid into the polymer matrix yields a composite with polydispersed filler and effective intrinsic thermal conductivities of up to 17 W m^-1 K^-1 (effective thermal conductivity of up to 10 W m^-1 K^-1). The LM-Cu colloid alloying into CuGa₂ provides a limited, but practical, time frame to cast the uncured composite into the desired shape, space, or void before the composite stiffens and cures with permanent characteristics.