A kinetics study of crystallization from discotic mesophases

The polymorphism of hexa-n-octanoate of rufigallol (RHO) was used to investigate the crystallization kinetics when starting from two different discotic mesophases, namely, a high-temperature enantiotropic mesophase and a low-temperature monotropic mesophase. In all cases, an Avrami exponent of n=3 was obtained, suggesting two-dimensional sporadic nucleation and growth. Although the same overall mechanism was predicted to operate for all crystallization temperatures investigated, the Avrami constant b has a temperature-dependence which is different for different starting columnar phases, indicating a strong influence on the rates of nucleation and of growth of the different molecular arrangements of the starting mesophases. Differential scanning calorimetry was used for the studies, supplemented by direct observations through optical polarizing microscopy.