Thermal conductivity, heat capacity and speed of sound of epoxy resins

Epoxy resins with enhanced thermal conductivity are in great demand to improve the thermal management of electrical motors. However, the thermal conductivity of epoxy resin is typically low, comparable to 0.2 W/m-K, and a predictive understanding of the connection between molecular structure and thermal conductivity is not yet established. Moreover, epoxy resins are usually cured by epoxies and hardeners, so there are thousands of combinations. Machine learning is an effective way to predict thermal conductivity of different combinations if sufficient data is provided. We established one efficient way (less than 8 minutes for each sample) to measure thermal conductivity, heat capacity and speed of sound of epoxy resin by frequency domain probe beam deflection (FD-PBD) and time domain thermoreflectance (TDTR). 80 combinations of epoxy and hardener have been studied. Small molecular structure difference is found to have a large influence on thermal conductivity of epoxy resin. For example, 5-chloro-m-phenylenediamine has thermal conductivity of 0.27 W/m-K, which is ~100% higher than o-phenylenediamine after curing with resorcinol diglycidyl ether. The differences of the two molecules are link site of amine groups and additional chlorine on benzene ring.