Oriented columnar films of a polar 1,2,3-triazole-based liquid crystal prepared by applying an electric field

Abstract

We report the electric-field (E-field)-assisted orientation of a bent-core liquid crystal (LC) based on the polar 1,2,3-triazolyl group. The LC exhibited a hexagonal columnar (COLhex) phase at ambient temperature, which transformed into a disordered columnar (COLdis) phase with short-range correlation upon heating. Dielectric relaxation spectroscopy and switching studies revealed that the aromatic cores could undergo in-plane rotation (a-relaxation) in the COLhex phase, while R-relaxation allowing the reorientation of the triazolyl units along the E-field direction occurred in the COLdis phase. Infrared spectroscopy confirmed that the hydrogen-bonding interactions between triazolyl units along the columnar axis affected the molecular motion. Based on the dynamics studies, two columnar alignment methods under E-fields, i.e., an isothermal method in the COLhex phase and a cooling method from the COLdis to COLhex phase were examined. Both methods give high-quality oriented columnar thin films. In particular, the cooling method requires less time (only 1 min) and a weaker E-field (10 V mu m(-1)), and therefore, it could be applied to the alignment of a bulk-level film (thickness: 260 mm). The successful orientation could be verified by in situ X-ray diffraction analysis under an E-field. The current-voltage curves before and after the alignment indicated that the orientation process enhanced electric conduction.