Dynamics of polyethersulfone phenylene rings: A quasielastic neutron scattering study

Abstract

By means of quasielastic neutron scattering, we have studied the hydrogen dynamics in glassy polyethersulfone, revealing the phenylene ring motions. The combination of a time-of-flight (TOF) and a backscattering spectrometer has allowed us to cover the microscopic and mesoscopic time scales (∼10-13−10-9 s) in a momentum transfer region well-suited to characterize local motions (∼0.4...2 Å-1). After a first step reflecting the fast processes undergone by the hydrogen below ∼2 ps, the decay of the intermediate scattering function can be described by the occurrence of a combined motion of the phenylene ring. This consists of π-flips and an additional process, faster and more restricted in space. We have interpreted this last motion as oscillations of increasing amplitude with temperature, which would emerge from the fluctuation of the local phenyl ring environment. Because of the structural disorder, both motions, π-flips and oscillations, show broadly distributed characteristic times, extending over several orders of magnitude. The coincidence of the activation energies for π-flips and γ-relaxation on one hand and for oscillations and δ-relaxation on the other hand confirms their respective strong correlation. Discrepancies in the absolute values of the corresponding characteristic times reflect, however, the higher complexity of the secondary relaxations in these kinds of systems.