GLASS-FORMING META-TOLUIDINE - A THERMAL AND STRUCTURAL-ANALYSIS OF ITS CRYSTALLINE POLYMORPHISM AND DEVITRIFICATION

The structural processes of transformation of the fragile glass former m-toluidine have been investigated by calorimetric (DSC) and X-ray ex periments with some additional kinetic studies of the devitrification process. Recrystallisation is found to be controlled by the passage of the undercooled liquid at temperatures well below the glass transitio n. This atypic behaviour is basically due to the formation of cracks w hich cause heterogeneous nucleation. However, an additional non-classi cal decrease of the nucleation barrier is suspected. The investigation of the phase diagram of the crystalline state itself has revealed an interesting monotropic situation between two phases alpha and beta wit h distinct X-ray diffraction patterns. This identification is useful i n the investigation of the medium-range order which may develop in the liquid state. (C) 1997 Elsevier Science B.V.