Nonlinear dielectric relaxation in the isotropic phase and mesophases of cholesteryl oleyl carbonate.
The nonlinear dielectric spectra of chiral crystal cholesteryl oleyl carbonate (COC) were recorded in frequency range of 1-100 MHz in the presence of the strong static electric field E(0) = 1 x 10(7) V/m. The measurements were performed within the temperature range of about 23 K in the isotropic, the blue phase, and the chiral nematic phase known also as the cholesteric phase. In the nonlinear dielectric relaxation spectra two absorption bands, related to molecular rotations (orientational band) and intermolecular interactions (chemical band), have been observed. The nonlinear dielectric results were interpreted by combination of a Debye-type and Coffey's equations, extended to the case of two simultaneous relaxation processes. The results revealed three regions in the temperature dependence of the chemical relaxation time behavior, corresponding to isotropic phase, blue phase and chiral nematic phase, respectively. Dynamic phenomena, observed in very narrow range of temperature (2 K) in the vicinity of the phase transition between the blue phase and the chiral nematic phase, were interpreted in frames of the Landau-de Gennes theory.
Kedziora
Przemysław
P
Institute of Molecular Physics, Polish Academy of Sciences, M. Smoluchowskiego 17, 60-179 Poznan, Poland. kedziora@ifmpan.poznan.pl
Wojciechowski
Krzysztof W
KW