Constructing 3D Skeletons for Enhanced Thermal Transport in Phase-Change Materials via Double-Percolated Structures

Abstract

An efficient 3D skeleton is essential to phase-change materials (PCMs) to address poor shape stability and low thermal conductivity. While double-percolated structures are effective in forming 3D filler networks, their achievement with 2D fillers remains challenging. We herein report the preparation of a hexagonal boron nitride (h-BN) skeleton for paraffin wax (PW, as the model PCM) by constructing double-percolated structures within poly(l-lactic acid) (PLLA)/low-density polyethylene (LDPE) blends, where h-BN preferentially localizes in the LDPE phase. 3D LDPE/h-BN skeletons with high porosity are achieved by removing the PLLA phase after solvent extraction. Notably, only 7.5 wt % of LDPE (the initial weight fraction in polymer composites) is sufficient for building a robust skeleton with 50 wt % h-BN, providing a large volume for accommodating PW after removing PLLA. A series of PW-based shape-stable PCMs with competent thermal conductivity, phase-change latent heat, and mechanical strength are prepared by vacuum-assisted impregnation. The obtained PCMs (namely, PPB-10, PPB-30, and PPB-50) exhibit thermal conductivity as high as 0.40, 0.56, and 0.87 W/(m·K). The phase-change latent heat (melting enthalpy) of PPB-10, PPB-30, and PPB-50 are 140.2, 104.2, and 77.8 J/g, respectively. PPB-50 demonstrates optimum performance in the heat management of an LED module, achieving a maximum temperature reduction of 33 °C during operation. The results highlight the crucial role of improving the thermal transport efficiency to fully activate the phase change of PCMs for effective thermal management.