Molecular dynamics and cold crystallization process in a liquid-crystalline substance with para-, ferro- and antiferro-electric phases as studied by dielectric spectroscopy and scanning calorimetry

In this article, molecular dynamics and the cold crystallization kinetics of 4-(6-heptafluorobutanoiloxyhexyloxy) biphenyl-4'-carboxylan(S)-4-(1-methyloheptyloxycarbonyl) phenyl (abbreviated as 3F6Bi and/or 4H6) are presented. Rich polymorphism of the liquid-crystalline (SmA*, SmC*, SmC*(A) and SmI*(A)) phases and partially disordered crystal CrI and glassy GCrI were observed upon cooling. Both, molecular and collective relaxation processes were observed in the para-, ferro- and antiferro-electric liquid-crystalline phases over the frequency range of 3 x 10(-2) to 3 x 10(6) Hz. An additional bias field in the dielectric experiments was used to identify individual processes. The high heating rates (5-10 K/min) phase sequence is the same as in case of the cooling experiment. On slow heating (0.5-2 K/min), cold crystallization of SmI*(A) to the more stable crystal CrII phase was observed in the dielectric and calorimetric experiments. The crystallization kinetics was analyzed using the Mo equation, which is a combination of the Avrami and Ozawa models. The activation energy of crystallization was calculated to be 138 and 99 kJ/mol using the Kissinger and Augis-Bennett models, respectively. (C) 2019 The Authors. Published by Elsevier B.V.