Static and dynamic contributions to anomalous chain dynamics in polymer blends

TL;DR

This study uses computer simulations to explore how static and dynamic factors influence the anomalous relaxation behavior of polymer chains in blends, revealing different mechanisms for flexible and semiflexible chains.

Contribution

It distinguishes static versus dynamic origins of anomalous chain dynamics in polymer blends, highlighting the role of chain stiffness and confinement effects.

Findings

Fully-flexible chains show dynamic-origin anomalous scaling.

Semiflexible chains exhibit static-origin anomalous scaling.

Static correlations remain unchanged despite dynamic asymmetry.

Abstract

By means of computer simulations, we investigate the relaxation of the Rouse modes in a simple bead-spring model for non-entangled polymer blends. Two different models are used for the fast component, namely fully-flexible and semiflexible chains. The latter are semiflexible in the meaning that static intrachain correlations are strongly non-gaussian at all length scales. The dynamic asymmetry in the blend is strongly enhanced by decreasing temperature, inducing confinement effects on the fast component. The dynamics of the Rouse modes show very different trends for the two models of the fast component. For the fully-flexible case, the relaxation times exhibit a progressive deviation from Rouse scaling on increasing the dynamic asymmetry. This anomalous effect has a dynamic origin. It is not related to particular static features of the Rouse modes, which indeed are identical to those of the fully-flexible homopolymer, and are not modified by the dynamic asymmetry in the blend. On the contrary, in the semiflexible case the relaxation times exhibit approximately the same scaling behaviour as the amplitudes of the modes. This suggests that the origin of the anomalous dynamic scaling for semiflexible chains confined in the blend is esentially of static nature. We discuss implications of these observations for the applicability of theoretical approaches to chain dynamics in polymer blends.