Defect structure and molecular motion in the four modifications of n -tritriacontane. I. Study of defect structure in the lamellar interfaces using small angle x-ray scattering

Abstract

The paraffin C₃₃H₆₈ undergoes three solid‐solid phase transitions between room temperature and the melting point. The orthorhombic modification (A) stable at low temperatures is followed by two different monoclinic forms (B: 54.5°C < T < 65.5°C; C: 65.5°C < T < 68°C) and by the ``rotator phase'' (D: 68°C < T < T_f=71.8°C). Defect structures as they occur in the three high temperature modifications were determined with the aid of small angle x‐ray scattering experiments. A method is applied which permits us to decide about the presence of different types of defects after a measurement of the absolute intensities of the 00l reflections. It was found that each one of the modifications B, C, D is characterized by a specific type of disorder. One observes orientational disorder of the skeletal planes in modification B, a superposition of longitudinal shifts of the chains in modification C, and an additional introduction of intrachain defects in modification D.