Journal of materials science vol:40 issue:7 pages:1661-1671
The kinetics of the high temperature ( isotropic. mesophase) and low temperature (mesophase --> crystalline) transition of PBFP at T-m and T (1), respectively, and its local dynamics were studied by differential scanning calorimetry (DSC) at variable heating and cooling rate and by dielectric relaxation spectroscopy (DRS). While on heating no substantial effect of the rate on both transition temperatures was found, T ( 1) and Tm showed a strong dependence on the cooling rate. The high temperature transition revealed thermally activated behaviour with an activation energy of E-a = 400 kJ/mol, whereas the transition at T ( 1) showed the typical signature of supercooling. This finding is consistent with the picture that the isotropic/mesophase transition at T-m is controlled by long-range, strongly hindered, chain diffusion that leads to the long-range orientational mesomorphic order. In contrast, the low temperature transition, the enthalpy of which is far larger and the temperature of which depending linearly on the cooling rate, indicates a kinetical control by nucleation as characteristic for a ( 2D --> 3D) crystallization process.