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

摘要

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 as an 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 140-330 K using a 1D steady-state conduction method, resulting in values of 0.34 ± 0.03 and 0.73 ± 0.07 W m~(-1) K~(-1) near room temperature and at 140 K, 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 48 h yielded nearly three-fold further improvement in thermal conductivity, achieving 0.97 ± 0.10 W m~(-1) K~(-1) at room temperature.