Relaxation dynamics and crystallization study of glass-forming chiral-nematic liquid crystal S,S-2,7-bis(4-pentylphenyl)-9,9-dimethylbutyl 9H-fluorene (5P-Am*FLAm*-P5)

Abstract

Abstract. The chiral nematic S,S-2,7-bis(4-pentylphenyl)-9,9-dimethylbutyl9H-fluorene (5P-Am*FLAm*-P5) liquid crystal shows a complex phase diagram strongly dependent on thermal treatment as identified by Polarizing Optical Microscopy (POM) and differential scanning calorimeter (DSC). The molecular dynamics in various thermodynamics states was studied by means of broadband dielectric spectroscopy (BDS). The vitrification of a chiral nematic phase (N*) is manifested by a Vogel-Fulcher-Tammann (VFT)-type temperature dependence of structural relaxation time ($\tau_{\alpha}$τα). Three dielectric relaxation processes exhibiting Arrhenius-like thermal activation were found in conformationally disordered (condis) Cr1 and Cr2 structures. The isothermal cold crystallization process of Cr2 occurs in the metastable N* phase; however, in the non-isothermal experiments, the Cr2 phase is formed in the isotropic phase obtained on heating the metastable N* phase. The findings for the isothermal process were compared with those regarding non-isothermal crystallization. Graphical abstract

Interplay between Melt and Cold Crystallization in a Smectic Liquid Crystal, 4-Pentylphenyl 4-(trans-4-Pentylcyclohexyl)benzoate

“…Cold crystallization is often found to be faster than melt crystallization . Our investigation implies that this tendency also applies to the crystallization of the mesophase, as observed in the previous studies of liquid-crystalline compounds. , As depicted in Figure e, the cold-crystallization process takes less time than melt crystallization independently of the crystallinity fraction gained upon cooling and heating. However, when the overall crystallization process is divided into two steps, i.e., melt and cold crystallization (ϕ ≥ 7 K min –1 ), the total crystallization time is prolonged (compare, e.g., the data for ϕ = 5 K min –1 and ϕ = 7 K min –1 in Figure e).…”

On relaxation and vibrational dynamics in the thermodynamic states of a chiral smectogenic glass-former

“…The registration of the stochastic molecular movements in the crystal phases is possible due to the presence of a chiral center in the molecule, 44 as well as the occurrence of fluorine atoms, which increase the number of dipole groups. 45 In the Cr2 phase, we notice one relaxation Cr (2) process (Fig.…”

Non-isothermal cold crystallization of liquid crystalline porphyrins

“…It appears that 3 forms multiple mesophases upon fast cooling, which has been observed for other rod- and disc-like molecules. 23–25…”

“…These relatively large entropies are similar to those reported for other cold crystallizing liquid crystals and are indicative of a highly organized crystalline phase with limited molecular motion. 22,23 Kinetic cold crystallization was not observed for 3 and 4 as upon cooling they crystallize rather than form supercooled amorphous solids, Fig. 1(c) and (d), respectively.…”