THE NATURE OF THE GLASS-TRANSITION IN A COLUMNAR HEXAGONAL ORDERED PHASE

The glass transition taking place in a columnar discotic phase is connected with the freezing-in of the correlated rotation of the disc-like molecules in the columns about the columnar axis. X-ray investigations on the temperature dependence of the linear expansion coefficients along the columnar axis and perpendicular to this axis reveal that the glass transition leads to a stepwise change of the expansion coefficient along the columnar axis and to a continuous variation for the corresponding coefficient perpendicular to this direction. The glass transition in such ordered systems is highly anisotropic both with respect to dynamic and to thermodynamic aspects.