Phase transitions in liquid crystal 6O.4 (p-n-hexyloxybenzylidine-p′-n-butylaniline)

Abstract

DSC measurements on p-n-hexyloxybenzylidine-p′-n-butylaniline (6O.4) showed that the crystalline to liquid crystalline (K-S _H) transition at 33.7°C observed in the heating cycle does not revert even when the sample is cooled down to −100°C. Hence it is inferred that a physically stable supercooled liquid crystalline phase is formed on cooling 6O.4. To investigate the K-S _H transition further the techniques of polarized microscopy and X-ray diffraction were used which concurred with the DSC results. Quasielastic neutron scattering measurements carried out to study the re-orientational motions in the ordered phases of 6O.4 (K and S _H) show that while in the crystalline phase (at RT) the re-orientational motion is found to involve only the core of the molecule, in the S _H phase (at 45°C) the dynamics involves the whole molecule and this motion is found to persist even when the sample cools back to room temperature corroborating the results of the DSC, microscopy and X-ray diffraction.