Enhancing thermal conductivity in polysiloxane composites through synergistic design of liquid crystals and boron nitride nanosheets

Polysiloxane-based thermally conductive composites are essential for electronic heat management, but they face challenges such as limited thermal conductivity enhancement and low improvement efficiency. In this work, a novel liquid crystal crosslinker (LCC) based on biphenyl liquid crystal moieties was synthesized. Liquid crystal polydimethylsiloxane (LC-PDMS) with intrinsic high λ was prepared by crosslinking vinyl/methyl-hydrogen functionalized PDMS by LCC at its liquid crystal transition temperature, and boron nitride nanosheets (BNNs) with different particle sizes were used to prepare BNNs/LC-PDMS composites. When the mass ratio of LCC to vinyl-terminated PDMS is 2:1, the LC-PDMS exhibitsa well-ordered liquid crystal phase, and its λ_∥ reachesthe maximum value of 0.34 W (m K)⁻¹, approximately 1.7 times that of general PDMS (0.20 W (m K)⁻¹). The λ_∥ of BNNs/LC-PDMS composites increases with the addition of BNNs, and when the mass fraction of BNNs reaches 30 wt%, with a 1:9 mass ratio of small BNNs (1 μm) to large BNNs (10 μm), the composite achieves the highest λ_∥ of 12.50 W (m K)⁻¹, a 68.5% increase compared to BNNs/PMDS composites containing the same amount of BNNs (7.42 W (m K)⁻¹). Additionally, BNNs/LC-PDMS composites also demonstrate excellent electrical insulation properties and low density, making them promising candidates for applications in highly integrated electronics fields.