Dielectric dispersion in a dual-frequency nematic liquid crystal 2-chloro-4-(4-pentylbenzoyloxy)benzoate

Abstract

Temperature dependences of dielectric dispersions in the homogenous and homeotropic alignment cells of 2-chloro-4-(4-pentylbenzoyloxy)benzoate (PCPB) were measured in the nematic phase in the frequency range between 100 Hz and 1 MHz. The obtained dielectric dispersions, ε$(ω) and ε$$(ω), could be explained using the Cole-Cole formula accounting for DC conduction. The parameter values in this formula were determined by the least-squares method. The frequency dependence of the dielectric anisotropy, including the dual-frequency characteristic, was well reproduced with our parameter values. The activation energy E a for molecular reorientation was estimated as approximately 9 ' 10 2 meV. The crossover frequency f c was approximately proportional to the relaxation frequency f r in PCPB.

Dielectric anisotropy in PCPB/MBBA mixtures showing the dual frequency characteristic

“…The real and imaginary parts of the dielectric dispersions, ( ) It is known that dielectric dispersions in LCs can be well described by the modified Debye-type function called the Cole-Cole function. 30) Note that the essential part of the Debye-type function can be derived from the Ladau-Khalatonikov equation of motion (see Sect. 4).…”

“…In our previous paper, 30) it was experimentally found that the crossover frequency f c is in proportion to the relaxation frequency…”

“…29) Recently, Takikawa et al reported their experimental results of the temperature dependences of dielectric dispersion in homogenously and homeotropically aligned cells in the nematic phase of PCPB, and found that dielectric dispersions can be explained by the Cole-Cole formula taking into account of DC conduction, and the crossover frequency f c and the relaxation frequency f r are proportional to each other. 30) The dual frequency characteristic was also found to appear even in PCPB-based mixtures, 16) especially in PCPB/MBBA (N-(4-Methoxybenzylidene)-4butylaniline) mixtures. However, unfortunately, as far as the authors know, no study of the dielectric dispersion in PCPB/ MBBA mixtures has been reported yet, despite being important for understanding the dual frequency nature.…”

“…Figure 7 shows an Arrhenius plot of [ ( ) ( ) ]/    e e t -¥ -0 1 .Although it was not possible to clarify the concentration dependence of the activation energy due to the poor accuracy, the activation energy E a in the S-mode is roughly estimated to be about 7 × 10 2 meV for all of concentrations.In our previous paper,30) it was experimentally found that the crossover frequency f c is in proportion to the relaxation frequency f r [ ( )] /…”

Dielectric dispersion in a dual-frequency smectic A liquid crystal PPEP(3F6)-CN/P(CN)P6-6 mixture

“…These features are similar to those of dual-frequency nematic LCs. 17) An Arrhenius plot constructed using the inverse of the relaxation time data is presented in Fig. 4.…”