Highly thermally conductive composites with boron nitride nanoribbon array

The traditional approaches to fabricate highly thermally conductive yet electrically insulating polymers relies mainly on adding massive ceramic fillers, which not only degrade the mechanical properties of polymers but also introduce more interfaces that lead to more scattering sites for phonons. Thus, it remains a major challenge to achieve high thermal conductivity with low filler content. Herein, to create directional conductors with fewer interfaces, we prepared array of vertically aligned hexagonal boron nitride nanoribbons (BNNRs) and then infused them with polydimethylsiloxane (PDMS). By optimizing the assembly density and crystalline structure of the BNNRs, the BNNR/PDMS composite achieves a remarkable through-plane thermal conductivity of 8.19 W/(m·K) at a low nanoribbon loading of 9.3 wt%, outperforming thermally conductive polymers with insulating fillers in spherical, fibrous, and flaky shapes at similar filler contents. Furthermore, high thermal–mechanical stability and outstanding electrical insulating properties are also discovered. In the thermal interface material (TIM) performance test, the BNNR/PDMS composite exhibits higher cooling efficiency than commercial TIMs, with a decrease in chip temperature of up to 16 °C, and maintains good thermal stability even after continuous heating–cooling processes of as long as 12 h.