Double dynamical regime of confined water

TL;DR

This study investigates the complex dynamics of water confined in silica pores, revealing a coexistence of slow, bound water and faster, free water, with a crossover to mode coupling transition during supercooling.

Contribution

It demonstrates the coexistence of two dynamical regimes in confined water and identifies the emergence of a crossover mode coupling transition in free water.

Findings

Identification of slow, frozen-like dynamics near the substrate

Confirmation of a mode coupling crossover in free water

Distinct dynamical regimes in different spatial layers

Abstract

The Van Hove self correlation function of water confined in a silica pore is calculated from Molecular Dynamics trajectories upon supercooling. At long time in the $\alpha$ relaxation region we found that the behaviour of the real space time dependent correlators can be decomposed in a very slow, almost frozen, dynamics due to the bound water close to the substrate and a faster dynamics of the free water which resides far from the confining surface. For free water we confirm the evidences of an approach to a crossover mode coupling transition, previously found in Q space. In the short time region we found that the two dynamical regimes are overimposed and cannot be distinguished. This shows that the interplay between the slower and the faster dynamics emerges in going from early times to the $\alpha$ relaxation region, where a layer analysis of the dynamical properties can be performed.