Insight into the Structure and Dynamics of Polymers by Neutron Scattering Combined with Atomistic Molecular Dynamics Simulations

Abstract

Combining neutron scattering and fully atomistic molecular dynamics simulations allows unraveling structural and dynamical features of polymer melts at different length scales, mainly in the intermolecular and monomeric range. Here we present the methodology developed by us and the results of its application during the last years in a variety of polymers. This methodology is based on two pillars: (i) both techniques cover approximately the same length and time scales and (ii) the classical van Hove formalism allows easily calculating the magnitudes measured by neutron scattering from the simulated atomic trajectories. By direct comparison with experimental results, the simulated cell is validated. Thereafter, the information of the simulations can be exploited, calculating magnitudes that are experimentally inaccessible or extending the parameters range beyond the experimental capabilities. We show how detailed microscopic insight on structural features and dynamical processes of various kinds has been gained in polymeric systems with different degrees of complexity, and how intriguing questions as the collective behavior at intermediate length scales have been faced.

Separation of the inelastic and elastic scattering in time-of-flight mode on the pinhole small-angle neutron scattering diffractometer KWS-2

“…2(c) and 2(d) the filled symbols represent the data collected at the rim of the detector (high scattering angles) while the open symbols show the data collected on the central part of the detector (small scattering angles), always on sectors of comparable detection area. Inelastic scattering is a Q-dependent process (Arbe et al, 2020). Therefore, the effect of the inelastic and quasi-elastic scattering processes can be better observed in the TOF spectra measured at higher scattering angles [full symbols in Figs.…”

Progress in neutron techniques: towards improved polymer electrolyte membranes for energy devices

“…ab initio methods, fully atomistic molecular dynamics-MD-simulations, Monte Carlo methods, etc). The data provided by NS are complemented by computational studies, where experimental parameters are used to feedback into model inputs, providing an effective methodology to understand the formation, stability, and properties of membrane materials, as well as guiding the formulation of advanced designs for specific applications [17,43,[47][48][49][50][51][52][53][54].…”

Disentangling Self-Atomic Motions in Polyisobutylene by Molecular Dynamics Simulations

“…Allowing free A, EISF, τ MG o and σ parameters the fits reproduced very well all the results (solid lines in the figure). Figure 8b shows the values obtained for the EISF parameter at 335 K (empty diamonds) as compared with the theoretical prediction Equation (16) There, the 'apparent EISF' obtained from the deconvolution approach (see the text) is shown by the solid circles. The continuous line is a description of these data within the experimental window explored in Ref.…”

“…Such deviations were investigated in more detail on PI with deuterated methyl groups by combining NS (backscattering and NSE) experiments with molecular dynamics (MD) simulations [14,15]. This combined approach results to be an extremely powerful tool, as it has been shown in a series of systems during the last years (see, e.g., [3,16]). To explain the behavior found for the hydrogen motions in PI, the so-called anomalous jump diffusion model was proposed.…”

“…With these ideas in mind, we have performed fully atomistic MD-simulations on PIB in a wide temperature range above T g . We have followed the strategy that has proved to be highly successful in previous studies that combined NS and MD-simulations [3,16]. First, the cell is validated by direct comparison of magnitudes computed from the simulation and measured by NS.…”