Quantitatively Predictable Filler Content Dependence of Inherent Thermal Conductivity of a Two‐Phase Composite of Boron Nitride and Polymer

ABSTRACT Pure two‐phase boron nitride (BN)/polystyrene composites were prepared from styrene, polystyrene, BN, and a small amount of polymerization initiator to study the inherent relationship between the thermal properties and filler content of BN/polymer composites, which has not been quantitatively elucidated. Owing to the highly wettable combination of filler–matrix materials and sufficient shear stress during the kneading process, dispersed two‐phase composite samples with controlled filler weight contents up to the filler‐dominant level (≤ 65 wt%) were successfully obtained. The thermal diffusivities and specific heat capacities of composites with various filler contents were measured. The thermal conductivity was quantitatively evaluated as a function of the filler volume fraction using the Agari–Uno model. The thermal conductivity increased exponentially as the filler content increased, owing to the increase in the filler‐to‐filler contacts. This is consistent with the dependence of the thermal conductivity on the filler content, as in conventional standard filler/matrix dispersion composite systems. Furthermore, analysis based on the Agari–Uno model indicated that BN filler alignment in the composite not only increased the thermal conductivity of the filler but also formed anisotropic thermal percolation, which promoted efficient heat transport, significantly enhancing the thermal conductivity of the composite.