Characteristic correlation between liquid crystalline epoxy and alumina filler on thermal conducting properties

As a promising matrix for developing efficient heat-dissipating materials, liquid crystalline epoxy resins (LCERs) have received much attention for a decade. Here, we present a comprehensive study including the synthesis, fabrication, and characterization of polymer/inorganic composites with a representative LCER, 4,4′-diglycidyloxybiphenyl (BP) epoxy. The thermal conducting properties of composites are systematically investigated by preparing a series of samples with various epoxy resins and alumina fillers. Notably, liquid crystalline BP composites show approximately 30% higher thermal conductivity compared to the composites of commercial epoxy with the same type of filler owing to the highly aligned microstructure of the LCER. In addition, the threshold loading of filler content required to construct an effective thermally conducting path in our system is in the range of 40-50 wt%. Furthermore, the thermal conductivity of BP composites can be controlled by incorporating various fillers differentiated by size and shape. In particular, the highest thermal conductivity among the BP composites with 80 wt% content of alumina is 6.66 W/m·K, which is significantly high for epoxy/alumina composites. The experimental results which agree well with the theory by Agari model reveal that the highly aligned microstructure of the LCER is essential requirement that should be considered to improve thermal conductivity of composites.