High-Thermal-Conductivity Flexible Boron Nitride Composite Films Enabled by the Directional Arrangement of Nanosheet Assemblies

The rapid development toward integration and miniaturization in microelectronic devices has triggered the urgent need for thermal interface materials (TIMs) with high thermal conductivity and electrical insulation. To be compatible with the rigidity of the electronic components and the heatsinks, it is imperative to synthesize high-performance TIMs that offer both excellent thermal conduction performance and flexibility, which remains a challenge. Here, we report the synthesis of flexible TIMs based on directionally assembled boron nitride nanosheets (BNNSs) with poly(vinyl alcohol) (PVA) as a binder. The BNNSs are produced by rapid quenching and ultrasound-assisted liquid-phase exfoliation, with a yield of up to 41%. Polyhexamethylguanidine hydrochloride (PHMG) acts as a bridge to connect the BNNS and PVA, thus improving the interfacial compatibility of the BNNS/PVA composites. Both theoretical simulation and experimental results suggest that the directional alignment of BNNSs with a high diameter-to-thickness ratio allows high thermal conductivity in both in-plane (23.6 W m –1 K –1 ) and through-plane (10.07 W m –1 K –1 ) directions. Using it as TIMs for LED chips, the device temperature can be significantly reduced by 15 °C. In addition to the excellent flame-retardant properties and wave transmission, the composite film exhibits extreme stability after thermal and cold shock cycles. This work provides a rational design for the thermal management of high-power-density electronic devices.