Nacre-inspired flexible and thermally conductive phase change composites with parallelly aligned boron nitride nanosheets for advanced electronics thermal management

Abstract

Phase change materials (PCMs) are widely applied in passive thermal management and energy storage fields because of their large latent heat capability near phase transition points. However, molten leakage, inherent rigidity, and low thermal conductivity limit the thermal management applications of PCMs. In this work, a scalable doctor-blading technique was developed to prepare anti-leakage, flexible, and highly thermally conductive PCM composites. Paraffin wax (PW) works as the thermal energy storage unit, polydimethylsiloxane (PDMS) encapsulates the molten PW and imparts the composites with flexibility, and 1-Butyl-3-methylimidazolium Hexafluorophosphate (BMIMPF6)-modified boron nitride nanosheets (BPs) ensure high thermal conductivity. BPs were firstly achieved from bulk boron nitride (BN) powders and BMIMPF6 ionic liquid (IL) by the one-step ball milling process, then high-oriented alignment of BPs in PDMS/PW matrix was obtained by the strong shearing forces along the blade-casting direction. Owing to the high quality of BPs and interconnected structure of BPs network, the composites possessed high in-plane thermal conductivity of 2.87 W·m⁻¹·K⁻¹ at 15 wt% BPs, exhibiting a remarkable enhancement of 1494 % compared with PDMS/PW. The flexible composites showed effective heat dissipation performance by reducing the working temperature of smartphones over 11 °C. Finite element analysis demonstrated that the parallel alignment of BPs network and the thermal energy buffering of PW were crucial for improving the thermal management capability. Furthermore, the PDMS/PW/BP composites exhibited excellent flame-retardant and electrically insulating properties. This work provides a feasible method to prepare high-performance PCM composites, which show great application prospects in the thermal management of electronic devices.