Solid-Solid Phase Transition of Hexatriacontane (n-C₃₆H₇₄)

Abstract

The solid-solid phase transition of hexatriacontane was investigated by X-ray diffraction and DSC thermal analyses. The results show that the crystalline c^*-axis remains unchanged during the transition. In a high purity specimen, the original monoclinic crystal once changes to the vertical structure and then transforms to the high temperature monoclinic form, where the molecular chain changes its staggering direction by 90°. In a lower purity specimen, the original orthorhombic crystal also changes into the high temperature monoclinic form. The interlayer spacing calculated from the crystalline structure shows that the high temperature monoclinic form is advantageous for molecular rotation. The irreversibility of the solid-solid transition is due to defects in the crystal caused by the change of the staggering direction.