Insight into cold- and melt crystallization phenomena of a smectogenic liquid crystal

Abstract

This paper describes the insight into the different nature of cold- and melt crystallization kinetics of a smectogenic liquid crystal.

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

“…In the temperature range of 170–400 K, the 3F5FPhH6 compound shows the isotropic liquid phase, three chiral smectic phases (paraelectric SmA*, ferroelectric SmC*, antiferroelectric SmC A *), and two crystal phases (Cr2, Cr1). The polymorphism of the smectic phases is in agreement with the previous results, 1 , 2 and the transition to the hexatic smectic phase, reported for 3F5HPhH6 and 3F5HPhH7, 12 − 14 is not observed. Even for fast cooling with the 30 K/min rate, 3F5FPhH6 undergoes crystallization to the Cr2 phase and the SmC A * glass is not obtained.…”

“… − Such a molecular structure leads often to the presence of the antiferroelectric smectic C A * (SmC A *) phase in a broad temperature range and with a high tilt angle; − therefore, the main purpose of the synthesis of the 3F m X 1 PhX 2 r compounds was their future potential use in the display technology, where the orthoconic SmC A * phase (characterized by a tilt angle of ca. 45°) enables the perfect dark state in a display. , The 3F m X 1 PhX 2 r compounds with m = 5 studied in details are 3F5HPhF4, 3F5HPhF6, 3F5FPhF6, 3F5HPhH6, and 3F5HPhH7. , Three of them are confirmed glassformers: 3F5HPhF4 and 3F5HPhF6 exhibit the vitrified SmC A * phase , and 3F5HPhH6 and 3F5HPhH7 exhibit the vitrified hexatic SmX A * phase, which is either SmI A * or SmF A *. − For 3F5FPhF6, the vitrification of the SmC A * phase has not been shown explicitly yet, but it is implied by a very low crystallization rate on cooling . The results from ref − show that the 3F m X 1 PhX 2 r compounds with m = 5 and r = 6 have a tendency to the glass transition of the chiral smectic phase for various fluorosubstitutions of the benzene ring, either both at the X 1 , X 2 positions, only at the X 2 position, or with no F atoms in the benzene ring.…”

“… 13 , 14 Three of them are confirmed glassformers: 3F5HPhF4 and 3F5HPhF6 exhibit the vitrified SmC A * phase 9 , 10 and 3F5HPhH6 and 3F5HPhH7 exhibit the vitrified hexatic SmX A * phase, which is either SmI A * or SmF A *. 12 − 14 For 3F5FPhF6, the vitrification of the SmC A * phase has not been shown explicitly yet, but it is implied by a very low crystallization rate on cooling. 11 The results from ref 10 − 12 show that the 3F m X 1 PhX 2 r compounds with m = 5 and r = 6 have a tendency to the glass transition of the chiral smectic phase for various fluorosubstitutions of the benzene ring, either both at the X 1 , X 2 positions, only at the X 2 position, or with no F atoms in the benzene ring.…”

“…7,8 The 3FmX 1 PhX 2 r compounds with m = 5 studied in details are 3F5HPhF4, 9 3F5HPhF6, 10 3F5FPhF6, 11 3F5HPhH6, 12 and 3F5HPhH7. 13,14 Three of them are confirmed glassformers: 3F5HPhF4 and 3F5HPhF6 exhibit the vitrified SmC A * phase 9,10 and 3F5HPhH6 and 3F5HPhH7 exhibit the vitrified hexatic SmX A * phase, which is either SmI A * or SmF A *. 12−14 For 3F5FPhF6, the vitrification of the SmC A * phase has not been shown explicitly yet, but it is implied by a very low crystallization rate on cooling.…”

“…Our aim is to check whether 3F5FPhH6 undergoes the glass transition in the smectic phase, as its counterparts with different types of fluorination, − to study the kinetics of crystallization and polymorphism in the solid state and to investigate the dielectric relaxation processes in the smectic and crystal phases. The results are further compared with other 3F m X 1 PhX 2 r compounds with m = 5. − …”