Neutron Scattering Studies of Self Diffusion in Rubbers and Polymer Melts

Abstract

Neutron incoherent scattering studies of simple liquids reveal that the classical translational motion of the molecules gives rise to a Doppler broadening of the elastic peak. From the band-width at half-peak height, measured as a function of Momentum transfer, the self-diffusion coefficient can be obtained for the translational motion of the molecules. Experiments on oligomers and high polymers of dimethylsiloxane show similar results, as do measurements of poly(propylene oxide), polyisobutylene and poly(ethylene oxide). Measurements on partially deuterated samples confirm that the effect arises from segmental diffusive motion, rather than rotations of pendant side-groups. The temperature dependence of this motion gives activation energies which are smaller than the activation energies for self-diffusion obtained from experiments of longer time-scale such as nuclear spin-lattice relaxation measurements and viscometry. © 1974, Walter de Gruyter. All rights reserved.