DYNAMIC INVESTIGATION OF THE SOLID-SOLID PHASE-TRANSITION OF NORMAL-ALKANE (HEXATRIACONTANE) BY SIMULTANEOUS MEASUREMENTS WITH DIFFERENTIALSCANNING CALORIMETRY, SMALL-ANGLE X-RAY-SCATTERING AND X-RAY TELEVISION DETECTOR

Simultaneous measurements have been performed using differential scann ing calorimetry, time-resolved small-angle X-ray scattering and X-ray television (TV) methods to study the solid-solid phase transition of t he normal-alkane (hexatriacontane) single crystal. The low-temperature monoclinic form (M-L) of hexatriacontane transforms to the high-tempe rature monoclinic form (M-H) by two mechanisms. One mechanism is a dir ect transition from M-L to M-H by twin formation without passing any a ctivated state. The other mechanism is a two-step transition through a n intermediate orthorhombic state (O), where the molecules stand up fr om the M-L state and then re-incline into the M-H state. The subsecond time-resolved investigation by simultaneous measurements reveals dyna mic variations during the transition. The former M-L --> M-H transitio n appears at a lower temperature showing that twin formation requires lower energy, than the two-step process with the activated state. Cont inuous changing of intensities observed in the X-ray TV indicates that the latter M-L --> O --> M-H transition is caused by the coherent mot ion of the molecules.