Fast dynamics in poly(vinyl chloride) below the glass transition. Self and pair correlation functions

Complete text of publication follows. In a previous work [1] the incoherent scattering function of Poly(vinyl chloride) (PVC) in the microscopic time range was successfully described in the frame of a model which assumes harmonic vibrations coexisting with relaxational contributions controlled by C-C torsional barriers. Moreover, it was possible to understand in the same frame the behaviour of the coherent scattering function measured on a deuterated PVC sample well above the glass transition temperature Tg [2]. In the present work, the applicability of such a model to coherent scattering of PVC below Tg is investigated. Within the experimental accuracy, the data cau be well described in terms of the coherent scattering function built starting from the results independently obtained from the study of the incoherent function [1]. This gives additional support to the ideas involved in our interpretation of the fast process in polymers as due to a trace of the behaviour of the system in absence of the effects (cooperativity, memory effects, correlations,...) which characterize the dense supercooled liquid like state against the normal liquid state. (author)