Hydrogen dynamics in polyethersulfone: A quasielastic neutron scattering study in the high-momentum transfer region

In a previous quasielastic neutron scattering study [I. Quintana, A. Arbe, J. Colmenero, B. Frick, Macromolecules 38 (2005) 3999] we characterized the hydrogen dynamics in glassy polyethersulfone as due to ‘fast processes’ plus flips and oscillations of the phenylene rings. Here we have extended this investigation by using thermal neutrons, that allowed exploring also much higher values of the momentum transfer Q. In the dynamic window accessed, a characterization as best accurate as possible of the fast dynamics is imperative in order to describe the experimental results, especially at very local length scales. While for Q ≲ 2.2 Å−1 (i.e., in the range previously studied) the proposed model perfectly describes the experimental data with the same parameters deduced from the earlier work, in the high Q-range (Q ≈ 3.5–4 Å−1) deviations are found. These could be overcome by assuming some kind of ‘effective softening’ of the fast process and slight deviations from harmonic behavior in the Q-dependence of the associated Debye–Waller factor.