Critical-like behavior of low-frequency dielectric properties in compressed liquid crystalline octyloxycyanobiphenyl (8OCB) and its nanocolloid with paraelectric BaTiO3

Abstract

The report presents pressure-related broadband dielectric spectroscopy (BDS) studies in liquid crystalline octyloxycyanobiphenyl (8OCB) and its nanocolloid with BaTiO3 paraelectric nanoparticles. It is focused on the low-frequency (LF) domain, and the impact of pretransitional fluctuations. Studies were carried out in isotropic liquid, nematic, Smectic A, and solid crystal phases. In each case, the critical-type behavior for the LF contribution to the real part of dielectric permittivity and DC electric conductivity is evidenced. Studies of dielectric constant, related to the static frequency domain, revealed in SmA mesophase the shift from the XY-type to the mean-field type criticality when adding nanoparticles. The ‘giant’ premelting effect, with the critical-like portrayal, in the solid crystal phase, is also evidenced. Studies are supplemented by the polarizing microscopy insight into all tested phases appearing on compressing in 8OCB, and the nanocolloid. Photos show prenematic fluctuations in the isotropic liquid phase, phase transitions, changes within nematic and smectic mesophases on compressing, and the impact of nanoparticles.