Precuring Matrix Viscosity Controls Thermal Conductivity of Elastomeric Composites with Compression-Activated Liquid and Solid Metallic Filler Networks

Polymer matrix composites with liquid metal droplet and solid particle fillers are promising candidates for thermal interface materials (TIMs) used in electronics thermal management. To achieve good thermal transport, the particle and droplet fillers must be interconnected to form thermally conductive percolation pathways in the polymer matrix. This in turn requires displacement of the polymer between fillers as well as rupture of the oxide shell on the liquid metal droplets. This study demonstrates a multipronged strategy to achieve extensive filler bridging and a high thermal conductivity polymer TIM pad. The strategy synergistically employs reactive solid and liquid microscale fillers, a polymer matrix with tuned precure viscosity, and mechanical compression during thermal curing of the composite. The data demonstrate that the viscosity of the precursor polymer solution prior to curing plays a major role in the resulting thermal conductivity. More specifically, samples made with low viscosity ≈100 cSt solutions achieve a high thermal conductivity of ≈15 W m⁻¹ K⁻¹ at a curing pressure of 2 MPa. This thermal conductivity is double that achieved with high viscosity ≈2300 cSt solutions. Since many polymer systems employed in industry and research have a high precure viscosity, this insight has important implications for next-generation TIMs.