Non-isothermal and isothermal cold crystallization of glass-forming chiral smectic liquid crystal (S)-4′-(1-methyloctyloxycarbonyl) biphenyl-4-yl 4-[7-(2,2,3,3,4,4,4-heptafluorobutoxy) heptyl-1-oxy]-benzoate

Molecular Dynamics and Kinetics of Isothermal Cold Crystallization in the Chiral Smectogenic 3F7FPhH6 Glassformer

“…The fragility parameter has the lowest value for 3F7HPhH6, making it the strongest glassformer among the three discussed compounds. There is also a significant difference in the cold crystallization mechanism between 3F7HPhH6 and the previously studied 3F7HPhF6 and 3F7HPhH7 [13,16]. For both 3F7HPhF6 and 3F7HPhH7, cold crystallization is controlled mostly by the diffusion rate, as the characteristic crystallization time decreases with the increasing temperature, according to the Arrhenius equation.…”

“…The results regarding the glass transition of the SmC * A phase and isothermal cold crystallization obtained herein for 3F7HPhH6 have been collected in Table 4, together with the corresponding results for 3F7HPhF6 (m = 7, X 1 = H, X 2 = F, r = 6, see Figure 1a) [12,13] and 3F7HPhH7 (m = 7, X 1 = H, X 2 = H, r = 7) [16,18]. Each compound differs from 3F7HPhH6 by one detail of the molecular structure: the fluoro substitution of the molecular core (3F7HPhF6) or the -C r H 2r+1 chain length (3F7HPhH7).…”

“…For both 3F7HPhF6 and 3F7HPhH7, cold crystallization is controlled mostly by the diffusion rate, as the characteristic crystallization time decreases with the increasing temperature, according to the Arrhenius equation. The activation energies determined by DSC (and XRD for 3F7HPhF6) are 79 kJ/mol [13] and 133 kJ/mol [16] for 3F7HPhF6 and 3F7HPhH7, respectively. For 3F7HPhH6, instead, the cold crystallization investigated by DSC does not show the Arrhenius dependence of τ cr (T), and both nucleation and diffusion have an equal impact on the crystallization kinetics.…”

“…The 3F7HPhH6 compound, chosen in this paper, was investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and broadband dielectric spectroscopy (BDS). The obtained results were compared with those already reported for the 3F7HPhF6 [12,13] and 3F7HPhH7 [16][17][18] compounds with a similar molecular structure, in order to discuss the influence of the F substituent and the length of the -C r H 2r+1 chain on the glassforming properties and cold crystallization kinetics. It was shown that 3F7HPhH6 has a smaller fragility index and crystallizes slower than the two previously studied compounds.…”

“…Moreover, the tilt angle in these compounds often approaches 45 • , which leads to the optical uniaxiality and, consequently, far better quality of the dark state compared to the SmC * A phase with the smaller tilt angle [10,11]. For a few of the mentioned fluorinated smectogens, the glass transition of the SmC * A phase was reported, even for slow cooling (1 K/min or at an even lower rate, enough to avoid crystallization) [12][13][14][15][16][17][18]. It allows for the obtainment of glass with anisotropic properties, whose practical application was already proposed both for smectic and nematic glassformers [19][20][21][22][23].…”