The X-Ray Study of the Molecular Motion in Polyethylene Crystal. I

Abstract

The temperature dependence of the integrated intensity of three Bragg reflections (020), (230) and (211) for polyethylene crystal has been measured in the temperature range from -90°C to 110°C. The temperature factor increases with increasing temperature. The anisotropy of the temperature factor has been obtained from the temperature dependence of the integrated intensity of three Bragg reflections. Below 0°C, the temperature factor is a linear function of temperature and the three components of the thermal average of the mean squared displacement agree with the theoretical values calculated by Kitagawa and Miyazawa using the harmonic approximation. Above 0°C, however, the temperature factor increases with more steep slope and the harmonic approximation is not satisfied. In this temperature range, the anharmonic lattice vibration may cause the increase of the temperature factor.