Kerr effect studies of the isotropic‐smectic phase transition of liquid crystalline 4‐nitrophenyl 4‐n‐alkoxybenzoates

Abstract

The static and dynamic pretransitional behaviour a t the isotropic-smectic A phase transition was investigated by the electric Kerr effect and compared with the behaviour a t the isotropic-nematic phase transition. Close above the smectic A-isotropic transition temperature a strong divergence end a deviation from the behaviour according t o the Landaude Gennes model (which was upheld far from the clearing temperature) was observed for both the Kerr constant and the Kerr relaxation time. The Kerr relaxation times near the smectic A-isotropic phase transition exceed that of the isotropic-nematic transition by more than a factor of 4 which is due to the existence of quasi smectic cybotactic groups in the isotropic phase.Das statische und dynamische Vorumwandlungsverhalten am Pheseniibergang isotropsmektisch A wird mit dem elektrischen Kerr-Effekt untersucht und mit dem Verhalten am Phasenubergang isotrop-nematisch verglichen. Dicht oberhalb der Phasenumwandlungstemperatur smektisch A-isotrop wird eine starke Divergenz und eine Abweichung vom Verhalten gemiiJ3 dem Landau-de Gennes Modell, das fern von der Kliirtemperatur gultig ist, fur die Kerr-Konstante und die Kerr-Relaxationszeiten beobachtet. Die Kerr-Relaxationszeiten nahe dem Phasenubergang isotrop-smektisch A sind um den Faktor 4 groaer als jene beim Phasenubergang isotrop-nematisch, was auf die Existenz von quasismektischen cybotaktischen Gruppen in der isotropen Phase zuruckzufuhren ist.

Nitro substitution in achiral calamitic liquid crystals

“…The opposite situation has been found for the corresponding lateral chloro substituted derivative [284,312] and the little understood dielectric relaxation mechanism in the mesophases [310], it is di cult to 10-4; this is due to the reduced dipole moment of the Cl group (m 5 1.59 D) in comparison with that of the nitro analyse these data (which have been used with the results of Kerr eOE ect experiments [144,223,298,314,317] for group [22]. Interestingly, terminal nitro substitution of the two-ring derivative presented in table 12, results in a the study of molecular dynamics in nitro derivatives [318] ).…”