Investigation of Chiral Smectic Phases and Conformationally Disordered Crystal Phases of the Liquid Crystalline 3F5FPhH6 Compound Partially Fluorinated at the Terminal Chain and Rigid Core

Abstract

Complementary methods are applied to investigate the phase transitions and crystallization kinetics of the liquid crystalline compound denoted as 3F5FPhH6. Two crystal phases are confirmed, and one of them is the conformationally disordered (CONDIS) phase. Complexity of the melt crystallization process is revealed by the analysis with Friedman’s isoconversional method. The melt crystallization of 3F5FPhH6 shows different mechanisms depending on temperature, which is explained by the relation between the thermodynamic driving force and the thermal energy of translational degrees of freedom. The studied compound crystallizes even during fast cooling (30 K/min), unlike similar compounds with different fluorosubstitutions of the benzene ring, which form the smectic glass for moderate cooling rates. The tendency to vitrification of the smectic phase decreases apparently with the decreasing stability width of the SmC A * phase and the increasing relaxation time of the collective relaxation process in this phase, at least for homologues differing from 3F5FPhH6 only by the type of fluorosubstitution.

Crystallization kinetics of (S)-4′-(1-methylheptyloxycarbonyl)biphenyl-4-yl 4-[4-(2,2,3,3,4,4,4-heptafluorobutoxy)but-1-oxy]-2-fluorobenzoate

“…As it was noticed in ref. 60 and 61, the intersection of the thermal energy of one or two translational degrees of freedom with the Δ S m ( T m − T ) function, 29 which describes the thermodynamic driving force of crystallization, may correspond to a temperature or temperature range characteristic for crystallization of a given compound. The plot for 3F4HPhF6 is presented in Fig.…”

“…The role of the translational degrees of freedom was indicated in the previous works regarding melt crystallization in similar compounds. 60,61 Molecules in the SmC A * phase have two translational degrees of freedom, corresponding to the movements within the smectic layer, and the thermal energy for each degree of freedom is RT/2. As it was noticed in ref.…”