Dielectric properties of three‐ring fluorinated compounds

Abstract

Four three-ring compounds, consisting of two cyclohexyl rings and one mono-or difluorinated phenyl ring, were studied using dielectric spectroscopy methods over a broad frequency range (1 kHz-3 GHz). They exhibit a nematic phase in a broad temperature interval, enriched by a smectic B phase in one case. The static and dynamic dielectric properties were analysed. It was established that the bridging CH 2 CH 2 group placed between cyclohexyl and phenyl rings considerably changes the reference frame of the molecule, unlike the situation when it links two cyclohexyl rings. In the nematic and smectic B phases the motion around the short axis is a Debye process, whereas the rotation around the long axis is split into two processes: independent rotation of the whole molecule and its fluorophenyl part.

Orientational Order of Difluorinated Liquid Crystals: A Comparative 13C-NMR, Optical, and Dielectric Study in Nematic and Smectic B Phases

“…This could suggest a role in generating some order biaxiality, as sensed by the aromatic fragment, played by the increased flexibility generated by the CH 2 CH 2 bridging group (linking one cyclohexylic unit with either the other cyclohexyl or the phenyl group), the presence of which represents the main structural difference among the compounds studied here and those of the previous study. Moreover, the highest biaxiality detected by NMR for 5CyCy2BF2 seems to agree with its sensibly different molecular shape, revealed by its peculiar dielectric properties, and ascribed to the location of the CH 2 CH 2 bridging group . In the smectic B phase of 5CyCy2BF2 , a constant trend for the orientational order is observed as a function of temperature.…”

“…Moreover, the highest biaxiality detected by NMR for 5CyCy2BF2 seems to agree with its sensibly different molecular shape, revealed by its peculiar dielectric properties, and ascribed to the location of the CH 2 CH 2 bridging group. 42 In the smectic B phase of 5CyCy2BF2, a constant trend for the orientational order is observed as a function of temperature. This trend is commonly found for B phases (smectic B and crystal B), 41,43,44 and it is probably due to the fact that orientational order no longer acts as a heat sink.…”

Nano-doped weakly polar versus highly polar liquid crystal

“…The value of dielectric anisotropy for doped D6AOB and 5CB sample at MHz frequency range decreases significantly, suggesting that ZONPs (1 % Cu) affect the parallel and perpendicular component of dielectric permittivity (e k and e ? ) (Belyaev et al 2000;Ouskova et al 2003;Czub et al 2008). The 5CB sample in the pure and doped form shows the same trend of dielectric anisotropy versus frequency curve and in the MHz region both the graph overlap.…”

Dielectric Relaxation in Liquid Crystalline Mixture Based on Cyanophenylpyridines

“…Диэлектрическая спектроскопия нематических жидких кристаллов (НЖК) позволяет не только получать важные диэлектрические характеристики, такие как проводимость, характерные времена релаксации, диэлектрическая проницаемость и ее анизотропия, но и изучать процессы молекулярной динамики НЖК [1][2][3]. В частности, вращательная динамика молекул НЖК обусловливает дисперсию диэлектрической проницаемости и смену ее знака в определенных нематических растворах [4][5][6][7].…”