The Slowdowns of Water Dynamics when Approaching a Glass Transition or a Solid Interface: A Common Rationale

TL;DR

This paper uses molecular dynamics simulations and a unified theoretical framework to explain the significant slowdown of water dynamics near glass transitions and solid interfaces, linking relaxation times to local structural changes.

Contribution

It demonstrates that water slowdown phenomena near interfaces and glass transitions can be described by a common theory involving local hopping and elastic distortions.

Findings

Theoretical framework successfully describes relaxation time variations.

Quantitative rationalization of glassy slowdown and Stokes-Einstein breakdown.

Relation between cage-rattling amplitude and relaxation dynamics established.

Abstract

Performing molecular dynamics simulations, we investigate the enormous slowdowns of water dynamics when approaching a glass transition or a solid interface. We show that both effects can be described on common grounds within a theoretical framework, which was recently proposed by Schweizer et al. and considers coupled local hopping and elastic distortion. For confined water, we correctly describe the variation of the alpha-relaxation time tau_alpha as a function of both temperature and position with respect to the interface. Exploiting our knowledge of a cooperative length scale xi(T) from the confinement studies, we quantitatively rationalize the glassy slowdown, tau_alpha(T), and the Stokes-Einstein breakdown of bulk water. For both confined and bulk liquid, variations of the alpha-relaxation time are intimately related to changes of the cage-rattling amplitude.