Enhanced configurational entropy in high-density nanoconfined bilayer ice

TL;DR

This paper introduces a new high-density bilayer ice phase with enhanced configurational entropy due to dual disorder levels, identified through molecular dynamics and density-functional theory simulations.

Contribution

It reports the discovery of a novel bilayer ice phase with unique disorder properties and higher entropy, expanding understanding of ice phases under nanoconfinement.

Findings

First-order transition between proton-ordered and proton-disordered phases

Crystalline oxygen lattice on a close-packed triangular structure

Configurational entropy twice that of bulk ice

Abstract

A novel kind of crystal order in high-density nanoconfined bilayer ice is proposed from molecular dynamics and density-functional theory simulations. A first-order transition is observed between a low-temperature proton-ordered solid and a high-temperature proton-disordered solid. The latter is shown to possess crystalline order for the oxygen positions, arranged on a close-packed triangular lattice with AA stacking. Uniquely amongst the ice phases, the triangular bilayer is characterized by two levels of disorder (for the bonding network and for the protons) which results in a configurational entropy twice that of bulk ice.