Multiple character of non-monotonic size-dependence for relaxation dynamics in polymer-particle and binary mixtures

TL;DR

This paper reveals that the relaxation dynamics in polymer-particle and binary mixtures exhibit multiple non-monotonic size-dependent extrema across various length scales, supported by simulations and mode-coupling theory.

Contribution

It demonstrates the emergence of multiple extrema in relaxation times as additive molecule size varies, extending understanding of size effects in complex mixtures.

Findings

Multiple extrema in relaxation times at different length scales.

Qualitative agreement between simulation and mode-coupling theory.

Interpretation based on local packing and dynamic coupling.

Abstract

Adding plasticizers is a well-known procedure to reduce the glass transition temperature in polymers. It has been recently shown that this effect shows a non-monotonic dependence on the size of additive molecules [The Journal of Chemical Physics 150 (2019) 024903]. In this work, we demonstrate that, as the size of the additive molecules is changed at fixed concentration, multiple extrema emerge in the dependence of the system's relaxation time on the size ratio. The effect occurs on all relevant length scales including single monomer dynamics, decay of Rouse modes and relaxation of the chain's end-to-end vector. A qualitatively similar trend is found within mode-coupling theoretical results for a binary hard-sphere (HS) mixture. An interpretation of the effect in terms of local packing efficiency and coupling between the dynamics of minority and majority species is provided.