Liquid crystalline phase in ethanol suspension of anisometric 4-cyano-4-n-hexylbiphenyl microcrystals: witnessed by dielectric spectroscopy

摘要

The suspensions of 4-cyano-4-n-hexylbiphenyl (6CB) anisometric microcrystal were obtained by quenching homogeneous 6CB/ethanol mixtures with different 6CB concentrations. Such suspensions were strongly suggested from the differential scanning calorimetry examinations and the image observations of the samples during the quench and heating processes. The crystallization process for the mixtures with higher 6CB concentration looked like the isotropic-nematic phase transition of bulk liquid crystal. Dielectric measurement was carried out on the mixtures during the heating process after quench. Distinct dielectric relaxation was observed in the frequency range between kHz and 100 kHz, which exhibited obvious dependence on temperature and 6CB concentration. Curve fitting on the complex conductivity spectra indicates that three Debye type relaxations exist in this narrow frequency range. Based on the dependences of relaxation parameters on temperature and 6CB concentration, the possible relaxation mechanisms and the phase conformation of the mixtures were discussed. It was concluded that the relaxations, from high to low relaxation frequency, originate from the Maxwell-Wagner polarization, the rotation of 6CB microcrystal around its long axis, and the reorientation of 6CB microcrystal around its short axis, respectively. It was also confirmed that the quenched 6CB/ethanol mixtures show isotropic-nematic phase transition with the increase of 6CB concentration.