Thermally Conductive\nPolydimethylsiloxane-Based Composite\nwith a Three-Dimensional Vertically Aligned Thermal Network Incorporating\nHexagonal Boron Nitride Nanosheets and Nanodiamonds

Thermal interface materials play a pivotal role in efficiently\ntransferring heat from heating devices to thermal management components,\nthereby reducing the risk of component degradation due to overheating.\nIn this study, we propose a strategy for enhancing the out-of-plane\nthermal conductivity (TC) of composite materials by fabricating a\nthree-dimensional (3D) thermal network within a polydimethylsiloxane\n(PDMS) matrix. Specifically, the composite material was designed to\nincorporate a dense thermal network comprising hexagonal boron nitride\nnanosheets (BNNSs) and nanodiamonds (NDs). The fabrication process\ncommenced with the preparation of BNNSs through liquid-phase exfoliation,\nfollowed by the creation of a 3D BNNSs-NDs/polyimide aerogel thermal\nframework using a unidirectional solidification ice templating method\nand subsequent heat treatment. Vacuum impregnation and curing were\nthen employed to finalize the production of the 3D BNNSs-NDs/PDMS\ncomposite material. Characterization analyses indicated that the addition\nof NDs filled the voids between BNNSs, leading to the densification\nof the thermal framework pore walls and the establishment of additional\nthermal pathways. Impressively, with concentrations of BNNSs and NDs\n of 17.99 and 7.71 wt %, respectively, the out-of-plane TC of the\n3D BNNSs-NDs/PDMS composite material reached 1.623 W m<sup>–1</sup> K<sup>–1</sup>, marking notable enhancements of 754.21% and\n256.70% compared to those of pure PDMS and composites prepared via\ndirect blending with randomly distributed BNNSs and NDs, respectively.\nFurthermore, the 3D BNNSs-NDs thermal framework improved the compressive\nstrength and the dimensional stability of the composite material.\nFinite element simulations additionally confirmed the synergistic\nimprovement of the TC achieved through the combination of BNNSs and\nNDs, demonstrating that the 3D BNNSs-NDs/PDMS composite material displayed\nsuperior heat conduction and a greater density of thermal pathways\ncompared to those of its counterparts, including 3D BNNSs/PDMS and\n3D NDs/PDMS composite materials. In summary, this work presents a\nstrategy for enhancing the out-of-plane TC of polymer-based composite\nmaterials by incorporating vertically aligned thermal networks.