Synergetic improvements of intrinsic thermal conductivity and breakdown strength in liquid crystal epoxy resin for high voltage applications

Heat conductive epoxy composites as electronic packaging materials present wider applications. However, the high loading of fillers required for a high thermal conductivity (k) inevitably degrades the electrical resistivity and breakdown strength (Eb) of epoxy composites, significantly limiting their urgent applications in high voltage fields. The key to tackling this dilemma is to improve the intrinsic k of pristine epoxy with inherently disordered structure. Liquid crystal epoxy (LCE) containing rod-shaped mesogenic units and flexible segments, emerges as a unique epoxy resin presenting inherently high-k realized via self-assembling the mesogens into ordered domains, represents a promising solution to this critical issue. In this work, two types of LCEs, i.e., BE and LCM6, were designed and synthesized, and their LC behaviors were investigated. Further, the thermal and electric properties of the 4,4-methylenedianiline cured BE/LCM6 were explored as a function of the LCM6 loading. The results reveal that the cured BE/LCM6 at an optimal ratio showcases the obviously elevated k and Eb along with low dielectric permittivity and loss, when compared with traditional epoxy and a single LCE component. The concurrent enhancement in both k and Eb is ascribed to the introduced ordered domains resulting from the self-assembled mesogens into the cured epoxy network, which pave the highway for phonon transport and impede the migration of charge carries. The prepared LCEs with high k and Eb show appealing application prospects in electrical power systems.