Collective dynamics of glass-forming polymers at intermediate length scales
A synergetic combination of neutron scattering, atomistic simulations and theoretical modelling
1 Centro de Física de Materiales (CSIC, UPV/EHU) and Materials Physics Center MPC, Paseo Manuel de Lardizabal 5, 20018 San Sebastián, Spain
2 Departamento de Física de Materiales (UPV/EHU), Apartado 1072, 20080 San Sebastián, Spain
3 Donostia International Physics Center, Paseo Manuel de Lardizabal 4, 20018 San Sebastián, Spain
Published online: 23 January 2015
Motivated by the proposition of a new theoretical ansatz [V.N. Novikov, K.S. Schweizer, A.P. Sokolov, J. Chem. Phys. 138, 164508 (2013)], we have revisited the question of the characterization of the collective response of polyisobutylene at intermediate length scales observed by neutron spin echo (NSE) experiments. The model, generalized for sublinear diffusion –as it is the case of glass-forming polymers– has been successfully applied by using the information on the total self-motions available from MD-simulations properly validated by direct comparison with experimental results. From the fits of the coherent NSE data, the collective time at Q → 0 has been extracted that agrees very well with compiled results from different experimental techniques directly accessing such relaxation time. We show that a unique temperature dependence governs both, the Q → 0 and Q →∞ asymptotic characteristic times. The generalized model also gives account for the modulation of the apparent activation energy of the collective times with the static structure factor. It mainly results from changes of the short-range order at inter-molecular length scales.
© Owned by the authors, published by EDP Sciences, 2015
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