Foam-like hierarchical hexagonal boron nitride as a non-traditional thermal conductivity enhancer for polymer-based composite materials

Abstract

Due to its high thermal conductivity, chemical stability, and electrically insulating nature, hexagonal boron nitride (h-BN) is a versatile material used in a wide range of demanding applications. Currently, commercial h-BN is manufactured as microparticles to be sintered or hot pressed into the desired shape, while for composite applications the microparticles are loaded into a polymer matrix. However, thermal resistance at the numerous particle–particle and particle–matrix interfaces within the resulting material can severely limit its effective thermal conductivity. In this work, the ability of contiguous, foam-like h-BN nanomaterials to act asan internal “scaffold” is investigated as a means of minimizing the negative influence of interfacial thermal resistances within h-BN/polymer composites. The h-BN foams were created using a simple atmospheric pressure chemical vapor deposition process, followed by various post-processing steps prior to being infiltrated with PMMA and cured. The thermal conductivity of the resulting h-BN/PMMA composites were tested over the temperature range of 140–330K using a 1D steady-state conduction method, resulting in values of 0.34±0.03 and 0.73±0.07Wm−1K−1 near room temperature and at 140K, respectively, for as-grown foam samples. With h-BN weight fractions of just 0.21–0.27%, the as-grown h-BN foam exhibited a specific thermal conductivity enhancement ten-fold greater than those reported for particulate-based composites. Furthermore, high temperature annealing of the h-BN foam in air for 48h yielded nearly three-fold further improvement in thermal conductivity, achieving 0.97±0.10Wm−1K−1 at room temperature.