Abstract
Solid-solid phase transition of n-C36H74 was investigated by DSC and X-ray diffraction methods. In the original monoclinic single crystal, molecular chains inclined about 27° in the bc-plane from the normal to the lamellar surface. During the transition started from 72°C and completed at 73.4°C, two kinds of mechanisms were observed in the formation of a high temperature monoclinic structure having the molecules inclined about 19° in the ac-plane. One mechanism was due to formation of twinned crystals where the transition was developed on the frontier of the (110) twin boundary. The twin formation was achieved by rotation of the molecular zigzag plane producing the new crystalline a-axis deviated by 67° from the original orientation. The other mechanism was attained by changing the molecular staggering by 90° where the crystalline axis was unchanged. In the solid-solid transition, the two mechanisms appeared simultaneously, resulting in the appearance of polycrystals.
