MERGING OF THE ALPHA-RELAXATION AND BETA-RELAXATION IN POLYBUTADIENE - A NEUTRON SPIN-ECHO AND DIELECTRIC STUDY

The local dynamics of 1,4 polybutadiene below and above the merging of the alpha and beta relaxations have been investigated by combining ne utron spin echo (NSE) and dielectric spectroscopy. The study of the dy namic structure factor measured by NSE over a wide momentum transfer r ange allows us to characterize the alpha relaxation as an interchain p rocess while the beta relaxation originates from mainly intrachain mot ions. At temperatures below the merging, the dynamic structure factor can be described by a superposition of elemental processes for the bet a relaxation as obtained from dielectric spectroscopy. The elemental m otions behind this process can be related to rotational jumps of the c hain building blocks around their center of mass. Furthermore, we have been able to consistently describe the dynamic structure factor above the merging of the alpha and beta relaxations by assuming that both p rocesses are statistically independent. In the framework of this scena rio a procedure for analyzing the dielectric response in the alpha-bet a merging region has been developed. Its application to the dielectric data allows us to describe the dielectric response in this region on the basis of the low temperature behavior of the alpha and beta proces ses and without considering any particular change in the relaxation me chanism of these processes. The temperature dependence found for the r elaxation time of the alpha process follows now the viscosity, a maske d feature in the experimental data due to the merging process. In this way, we have been able to consistently describe the relaxation of bot h, the polarization and the density fluctuations, by using the same sc enario, i.e., independent alpha and beta processes, and considering th e same functional forms and temperature dependences of the characteris tic times of the two processes.