Two-dimensional partitioned square ice confined in graphene/graphite nanocapillaries

TL;DR

This study uses molecular dynamics simulations to explore the formation of multidirectional partitioned square ice patterns in confined water between graphene/graphite layers, revealing key energetic and structural factors influencing pattern formation.

Contribution

It introduces the concept of partitioned square ice patterns and analyzes their formation mechanisms under different confinement conditions and parameters.

Findings

Partitioned square ice patterns are more stable for n >= 2 graphene layers.

Formation of partitioned patterns is energetically unfavorable in single-layer water.

Pressure and temperature influence the transition between partitioned and homogeneous square ice.

Abstract

As one of the most fascinating confined water/ice phenomena, two-dimensional square ice has been extensively studied and experimentally confirmed in recent years. Apart from the unidirectional homogeneous square icing patterns considered in previous studies, the multidirectional partitioned square icing patterns are discovered in this study and characterized by molecular dynamics (MD) simulations. Square icing parameters are proposed to quantitatively distinguish the partitioned patterns from the homogeneous patterns and the liquid water. The number of graphene monolayers n is varied in this study, and the results show that it is more energetically favorable to form partitioned square icing patterns when the water molecules are confined between graphite sheets (n >= 2) compared to graphene (n = 1). This phenomenon is insensitive to n as long as n >= 2, because of the short-range nature of the interaction between water molecules and the carbon substrate. Moreover, it is energetically unfavorable to form partitioned square icing patterns for a single layer of water molecules even for n >= 2, verifying that the interaction between layers of water molecules is another dominant factor in the formation of partitioned structures. The conversion from partitioned structure to homogenous square patterns is investigated by changing the pressure and the temperature. Based on the comprehensive MD simulations, this study unveils the formation mechanism of the partitioned square icing patterns.