Cold crystallization from chiral smectic phase

Cold crystallization of liquid crystalline (S)-4'-(1-methylheptyloxycarbonyl)biphenyl-4-yl 4-[ 7-(2,2,3,3,4,4,4-heptafluorobutoxy) heptyl-1-oxy]-2-fluorobenzoate (3F7HPhF) was studied in isothermal as well as non-isothermal conditions. For isothermal conditions at temperatures between 233 and 250 K X-ray diffraction and differential scanning calorimetry were used. The crystallization kinetics was described by the Avrami-Avramov model, and the values of Avrami exponent, characteristic time and activation energy were determined. The kinetics of the cold crystallization in non-isothermal conditions for chosen heating rates up to 0.5 K/s was studied by differential scanning calorimetry and analyzed using Ozawa, Mo and Augis-Bennett models. Cold crystallization was found to be three-dimensional and controlled by diffusion both in the isothermal and non-isothermal process, however the activation energy determined in the non-isothermal process is about two times smaller than in the isothermal one.