Dielectric and orientational properties of nematogenic 4-n-octyl(4′-cyanophenyl)benzoate

Abstract

Experimental studies of the dielectric properties in the nematic and isotropic phases of 4-cyanophenyl-4′-n-octylbenzoate (8CPB) have been performed in the frequency range from 50 kHz to 100 MHz. The relaxation process related to the rotation around the short molecular axis has been analysed. The results obtained have revealed that in the vicinity of the I-N phase transition, the molecular subdiffusional rotation process occurs. It is connected with the pretransitional effects which are observed both in the static and dynamic dielectric measurements. On the basis of the temperature dependence of the relaxation time in the nematic and isotropic phases, the orientational order parameter 〈P2〉 has been determined. The values of 〈P2〉 obtained in this way have been compared with those evaluated from the measurements of the polarized electronic absorption of the dichroic dye, dissolved as guest probe in the mesogenic host.

‘Quasi-Tricritical’ and Glassy Dielectric Properties of a Nematic Liquid Crystalline Material

“…. and to more complex as 'cybotactic groups' appearing in the LC material as the substitute of pretransitional (prenematic fluctuations) [3,4,[56][57][58][59][60]. There are also claims that the observed weakly first-order nature of the N-I transition must be traced at the level of molecular interactions because just before the phase transition to the nematic phase the relaxation rate (linked to the relaxation time) strongly decreases from several 10 kHz down to a few kHz.…”

Prenematic Self-Assembling of Mesogenic Molecules in Isotropic Liquid and Orientational Order in Nematic Phase

“…As it is seen, the P 2 values for 8OCFPB and 8OCPFB obtained from the optical spectroscopy are significantly greater than those calcu-lated from the retardation factor. Such a result was also obtained earlier for 8CB [24], and it is common for a lot of liquid crystals for which some different methods yielded distinct values of P 2 [30,31]. It is also evident that, on contrary to the dielectric method, the position of the fluorine atom in the investigated molecules influences the values of P 2 determined from the optical absorption.…”

“…Constant values of g are also expected in the temperature range of the nematic phase. When approaching the phase transition in the isotropic phase, if g < 1, one can observe the decrease of the g factor as a result of the antiparallel associations increase [24]. The prenematic fluctuations in the isotropic phase near the phase transition seem to be correlated with the changes in molecular associations, as it was found earlier [5].…”

“…For nCHBTs g = 1 [24] which indicates the lack of molecular associations, and, as a consequence, the dielectric pretransitional effect is not observed in this case.…”

Comprehensive review on Froehlich entropy estimation: a technique to investigate the state of order in condensed matter

“…The first experimental use of Fröhlich equations and interpretation were carried out in 2003 by Gianbattista Parravicini et al for the investigation of melting processes in confined metallic nanoparticles [38][39][40]. Subsequently, Fröhlich arguments were fruitfully applied on the study of nematic compounds [41][42][43][44][45], molecular crystals [46,47],…”