Uniaxial–Biaxial Nematic Phase Transition in Combined Main-Chain/Side-Chain Liquid Crystal Polymers Using Self-Consistent Field Theory

Abstract

We investigate the isotropic–anisotropic phase transitions and the conformation of combined main-chain/side-chain liquid crystal polymers (MCSCLCPs) by numerically solving semiflexible chain self-consistent field theory (SCFT) equations with the pseudospectral method. Two kinds of interactions are involved: the global coupling between backbone segments, between the backbone and side groups, and between the side mesogens and the local coupling between the polymer backbone and its attached side groups. When the hinges are flexible, both global and local effects prefer parallel alignments of backbone and side groups, forming only prolate uniaxial nematic phase NPIII. When the hinges are relatively stiff, the competition between the global interaction preferring parallel orientations of the system and the perpendicular tendency of the two components due to the comb architecture results in rich phases with various orientation modes, including uniaxial prolate phases NPI, NPII, and oblate phase NO and biaxial phases NBI, NBII, and NBIII. The new phases NO and NBIII have not yet been reported by the previous theoretical results. We conclude that the occurrence of the biaxial phases results from not only the perpendicular toplogical structures between the oriented main chain and side groups but also the bending feature of the wormlike chain backbone, another necessary condition for NBI and NBII.