Mesophase Transformation of Mixed Liquid Crystals Formed by Supramolecular Self‐Organization of 4‐Substituted Benzoic Acids

Abstract

AbstractA mixed liquid crystalline system consisting of 4‐(octadeca‐1,3‐diynyl)benzoic acid (14PhDA) and 4‐tetradecanoxybenzoic acid (14OBA) exhibits different mesophases depending on their composition and the temperature. A mechanism is investigated for the formation of mixed liquid crystalline phases and the transformation of smectic to discotic lamellar mesophases. The three kinds of mesophases, the discotic columnar phase of 14PhDA, the smectic C phase of 14OBA, and the discotic lamellar phase of a mixture of 14PhDA and 14OBA, are simultaneously observed in a temperature range from 110 to 140 oC during the process of formation of the mixed liquid crystals by the molecular diffusion of 14PhDA and 14OBA. After rapid cooling the sample to room temperature, microscopic IR spectra are measured to estimate the composition ratio of 14PhDA and 14OBA at local positions in each mesophase. The composition ratio discontinuously changes at the boundary between the 14OBA and 14PhDA/14OBA phases due to a significant difference in the mesophase structures, i. e., the calamitic and the discotic phases, while the 14PhDA content continuously increases at another boundary between the 14PhDA/14OBA and 14PhDA mesophases. It is concluded that the diffusion of 14OBA dimer from the smectic phase to the discotic lamella phase is fast in contrast to the slow diffusion of disc‐like mesogens included in the discotic mesophases.