Dynamic Investigation of the Solid-Solid Phase Transition of Normal-Alkane (Hexatriacontane) by Simultaneous Measurements with Differential Scanning Calorimetry, Small-Angle X-Ray Scattering and X-Ray Television Detector

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Simultaneous measurements have been performed using differential scanning calorimetry, time-resolved small-angle X-ray scattering and X-ray television (TV) methods to study the solid-solid phase transition of the normal-alkane (hexatriacontane) single crystal. The low-temperature monoclinic form (M_L) of hexatriacontane transforms to the high-temperature monoclinic form (M_H) by two mechanisms. One mechanism is a direct transition from M_L to M_H by twin formation without passing any activated state. The other mechanism is a two-step transition through an intermediate orthorhombic state (O), where the molecules stand up from the M_L state and then re-incline into the M_H state. The subsecond time-resolved investigation by simultaneous measurements reveals dynamic variations during the transition. The former M_L → M_H transition appears at a lower temperature showing that twin formation requires lower energy, than the two-step process with the activated state. Continuous changing of intensities observed in the X-ray TV indicates that the latter M_L → O → M_H transition is caused by the coherent motion of the molecules.
社団法人応用物理学会の論文
1997-09-15