Enhancing the thermal conductivity of silicone composites by increasing crosslink degree

In this contribution, for the first time, the effect of crosslink degree on the thermal conductivity of silicone-based thermal conductive materials has been experimentally investigated. Hyper-branched silicone bases with different branching degrees and cross-linkable functional group densities are designed and synthesized via a one-pot, simple and efficient route. The resulting silicone bases can be efficiently cured by the agents containing the silicone-hydrogen functional group under the catalysis of platinum complex, giving hard and relatively brittle solids, rather than soft elastomer-like products obtained from commercial silicones with much lower crosslink density. Interestingly, with increasing the loading ratio of ceramic nanoparticles, the composites with the homemade silicones as the base become very stiff, and exhibit much higher thermal conductivity than the commercial ones with up to 50% enhancement, although the thermal conductivity of pure self-made silicones is similar to that of commercial silicones. This can be attributed to more energy transfer pathways along covalent bonding and reduced free volume in the composites with higher crosslink degree, demonstrating an effective approach to enhance the thermal conductivity of silicone-based thermal conductive materials. By using our self-made silicones, a novel thermal conductive material with both good transparency and high thermal conductivity has been developed potentially for die attach materials and LED encapsulants.