Non-exponential Rouse correlators and generalized magnitudes probing chain dynamics

Abstract

Inspired by the generalized Langevin equation (GLE) formalism with some approximations, we have proposed a method to generalize the Rouse expression of the magnitudes probing chain dynamics, taking into account the non-exponential character of the Rouse mode correlators. In this way, generalized expressions for the incoherent neutron scattering function and for the End-to-End relaxation - which give rise in the frequency domain to the dielectric 'normal mode' relaxation - have been obtained. These magnitudes have been checked by means of fully atomistic molecular dynamics (MD) simulations corresponding to pure poly(ethylene oxide) (PEO) and to PEO in an asymmetric blend with poly(methyl methacrylate) (PMMA). Moreover, the results obtained also seem to give support to the unified scenario recently proposed for explaining the non-exponential relaxation of the long-wavelength Rouse modes in polymer systems in terms of the effect of density fluctuations (α-process) on chain dynamics.