Confinement effect on phase transitions of a discotic liquid crystal: a calorimetric study

Differential scanning calorimetry was used to investigate the confinement e ffects on the phase transition behaviour of a discotic liquid crystal. The liquid crystal studied is the hexa-n-octanoate of rufigallol (RHO); Millipo re membranes of various pore sizes were the confining materials. The polymo rphism of RHO is affected by confinement. The transition from an enantiotro pic columnar phase(D1) to a monotropic columnar phase (D2) is supressed in membranes with pore sizes less than or equal to 500 Angstrom. The transform ation from D1 to the crystalline phase is also perturbed, particularly in t he membrane having an average pore size of 250 Angstrom. In the first case the crystal formed displays a double-melting endotherm, with a distinct str ucture melting at lower temperatures; in the other, the induction period of isothermal crystallization becomes longer and the global rate of crystalli zation is slowed. However, confinement shows no effect on the overall cryst allization mechanism. a similar Avrami constant of n similar to 3 was obtai ned for both confined and bulk RHO. An analysis of the results is presented .