Pretransitional effects of the isotropic liquid-plastic crystal transition

TL;DR

This paper reports novel pretransitional effects in the isotropic liquid-plastic crystal transition, including the first experimental observation of Mossotti Catastrophe behavior and a temperature-driven crossover in a plastic crystal, supported by a minimal theoretical model.

Contribution

It presents the first experimental evidence of pretransitional effects in plastic crystals and introduces a minimal model to describe their phase behavior.

Findings

Observation of Mossotti Catastrophe behavior in cyclooctanol

Detection of a temperature-driven crossover in nematic phase

Parallel with liquid crystal phase transition behavior

Abstract

We report on strong pretransitional effects across the isotropic liquid-plastic crystal melting temperature in linear and nonlinear dielectric response. Studies were carried out for cyclooctanol (C8H16O) in the unprecedented range of temperatures 120 K < T < 345 K. Such pretransitional effects have not yet been reported in any plastic crystals. Results include the discovery of the experimental manifestation of the Mossotti Catastrophe behavior, so far considered only as a hypothetical paradox. The model interpretations of experimental findings are proposed. We parallel the observed pretransitional behavior with the one observed in octyloxycyanobiphenyl (8OCB), typical liquid crystal (LC), displaying a reversed sequence of phase transitions in orientational and translational degrees of order on varying temperature. Furthermore, in its nematic phase, we demonstrate first-ever observed temperature-driven crossover between regions dominated by isotropic liquid and smectic A pretransitional fluctuations. We propose a pioneering minimal model describing plastic crystal phase behavior where we mimic derivation of classical Landau-de Gennes-Ginzburg modelling of Isotropic - Nematic - Smectic A LC phase behavior.