Investigation of crystallization kinetics and its relationship with molecular dynamics for chiral fluorinated glassforming smectogen 3F5HPhH6

The phase transitions, crystallization kinetics and molecular dynamics of (S)-4 '-(1-methylheptylcarbonyl)biphenyl-4-yl 4-[5-(2,2,3,3,4,4,4-heptafluorobutoxy)pent-1-oxy] benzoate (3F5HPhH6) are investigated by differential scanning calorimetry, polarizing optical microscopy and broadband dielectric spectroscopy. The vitrification of the antiferroelectric hexatic phase is observed for cooling rates >= 5 K min(-1) and the fragility index determined from dielectric data is m(f) approximate to 90. Two regimes of non-isothermal cold crystallization are distinguished using the Kissinger and Augis-Bennett methods in the heating rate ranges of 1-5 K min(-1) (larger activation energy) and 8-20 K min(-1) (lower activation energy). The correlation between the time of non-isothermal cold crystallization (using isothermal approximation) and relaxation time of the alpha-process is determined. The obtained coupling coefficient xi approximate to 0.7 and temperature dependence of the crystallization rate Z from the Ozawa model imply a mainly diffusion-controlled cold crystallization below 275 K. The Avrami exponents n and Ozawa exponents n(O) determined for isothermal melt crystallization and non-isothermal cold crystallization, respectively, weigh in favour of two- rather than three-dimensional crystal growth. The transition between crystal phases is observed on heating, with a lower activation energy for 1-3 K min(-1) than for 5-20 K min(-1) rates.

Automated summary

The study investigated the phase transitions, crystallization kinetics, and molecular dynamics of a specific organic compound, revealing the vitrification of the antiferroelectric hexatic phase, different behaviors of non-isothermal cold crystallization at various heating rates, and the temperature dependence of the crystallization rate. The results suggest a mainly diffusion-controlled cold crystallization process and favor two-dimensional crystal growth rather than three-dimensional growth. The lower activation energy observed during heating indicates a transition between crystal phases at different rates.