A KINETICS STUDY OF CRYSTALLIZATION FROM DISCOTIC MESOPHASES

The polymorphism of hexa-n-octanoate of rufigallol (RHO) was used to i nvestigate the crystallization kinetics when starting from two differe nt discotic mesophases, namely, a high-temperature enantiotropic mesop hase and a low-temperature monotropic mesophase. In all cases, an Avra mi exponent of n=3 was obtained, suggesting two-dimensional sporadic n ucleation and growth. Although the same overall mechanism was predicte d to operate for all crystallization temperatures investigated, the Av rami constant b has a temperature-dependence which is different for di fferent starting columnar phases, indicating a strong influence on the rates of nucleation and of growth of the different molecular arrangem ents of the starting mesophases. Differential scanning calorimetry was used for the studies, supplemented by direct observations through opt ical polarizing microscopy.