MOLECULAR-DYNAMICS IN PERFLUORO-N-EICOSANE .3. OSCILLATORY AND DIFFUSIVE TRANSLATIONAL MOTION

The translational motion of C20F42 helices is investigated using a combination of x-ray scattering and coherent quasielastic and inelastic neutron scattering techniques. In phase I, the helices are ordered with respect to their orientation and the dominating mode of motion is an acoustic phonon. In the high temperature phase R, the helices are disordered with respect to their longitudinal position and the angle of rotation around their main axis. Neutron scattering reveals for the longitudinal disorder a wide spectrum of relaxation times (10(-12)-10(-9) s). The rotational ordering of the helices leads to increased correlations and a slowing down in the diffusive longitudinal dynamics already above the phase transition.