Supercooled water confined in a metal-organic framework

TL;DR

This study investigates the molecular dynamics of supercooled water confined in a metal-organic framework, revealing that confinement influences water's glass transition and suggests the existence of two distinct length scales in water's structure.

Contribution

It provides new insights into the behavior of supercooled water in confinement, highlighting the existence of two different length scales and their relation to water's dynamic properties.

Findings

Supercooled water in confinement exhibits dynamics similar to bulk water outside the no-man's land.

A different form of water forms under confinement, still undergoing a glass transition.

Two length scales, approximately 2 nm and greater than 2 nm, are associated with water's structure and dynamics.

Abstract

Within the so-called "no-man's land" between about 150 and 235 K, crystallization of bulk water is inevitable. The glasslike freezing and a liquid-to-liquid transition of water, predicted to occur in this region, can be investigated by confining water in nanometer-sized pores. Here we report the molecular dynamics of water within the pores of a metal-organic framework using dielectric spectroscopy. The detected temperature-dependent dynamics of supercooled water matches that of bulk water as reported outside the borders of the no-man's land. In confinement, a different type of water is formed, nevertheless still undergoing a glass transition with considerable molecular cooperativity. Two different length scales seem to exist in water: A smaller one, of the order of 2 nm, being the cooperativity length scale governing glassy freezing, and a larger one (> 2 nm), characterizing the minimum size of the hydrogen-bonded network needed to create "real" water with its unique dynamic properties