Mechanical and thermal properties of liquid crystalline epoxy thermosets

Liquid crystalline epoxy resins containing mesogenic groups were cured under controlled temperature conditions to suppress the molecular mobility and promote crosslinking while maintaining an ordered alignment structure. The resulting alignment of polymer network chains in the cured materials was thoroughly characterized using polarized optical microscopy (POM) and X-ray diffraction (XRD). By varying the curing temperature, significant changes were observed in the domain size of the aligned liquid crystalline phases. These phases were identified as either nematic or smectic liquid crystal structures, which were found to be retained and fixed within the polymer network. The mechanical and thermal properties of the cured liquid crystalline epoxy thermosets were evaluated, and their relationship with the alignment structure of the network chains was discussed. In particular, fracture toughness was found to increase markedly with the enlargement of the liquid crystalline domains, indicating that the anisotropic order contributes to enhanced energy dissipation during the crack propagation.

Furthermore, the incorporation of cellulose nanofibers (CNFs) into the curing system led to an increased proportion of smectic liquid crystalline alignment. This enhancement is attributed to the hydroxyl groups present on the surface of the CNFs, which likely induced alignment of the liquid crystalline epoxy matrix through polar interactions.