Edge-Driven Phase Transitions in 2D Ice

Abstract

water, confined by atomically flat layered materials, may transit into various crystalline phases even at room temperature. However, to gain full control over the crystalline state, we should not only confine water in the out-of-plane direction but also restrict its in-plane motion, forming 2D water clusters or ribbons. One way to do this is by using an electric field, in particular the intrinsic electric field of an adjacent polar material. We have found that the crystalline phases of 2D water clusters placed between two hexagonal boron nitride (h-BN) nanoribbons are crucially determined by the nanoribbons' edges, the resulting polarity of the nanoribbons, and their interlayer distance. We make use of the density functional theory with further assistance of molecular dynamics simulations to establish the comprehensive phase diagrams, demonstrating transitions between liquid and solid phases and between the states of different crystalline orders. We also show that the crystalline orders are maintained when water flows between h-BN channels under external pressure. Our results open a promising pathway toward the control of the water structure and its flow by the use of the microscopic electric field of polar materials.

New insights into the interactions between two‐dimensional ice and two‐dimensional materials

“…Moreover, MD simulations have been developed to predict the properties of 2D ice/water confined within specific 2D layered materials such as graphene, 50 MoS 2 , 33 and h-BN. 51 These simulations have considered various external conditions and vdW interactions at the respective interfaces. For example, water molecules confined between two single-layered graphene sheets can withstand an internal pressure of approximately ~1 GPa due to the vdW force between the layers, resulting in the formation of 2D cubic ice.…”

“…Moreover, MD simulations have been developed to predict the properties of 2D ice/water confined within specific 2D layered materials such as graphene, 50 MoS 2 , 33 and h‐BN 51 . These simulations have considered various external conditions and vdW interactions at the respective interfaces.…”

Variation of Critical Crystallization Pressure for the Formation of Square Ice in Graphene Nanocapillaries

“…Thus, the existence of low-dimensional ice can be facilitated or suppressed by the design of capillary length in practical applications, according to the interrelation between the length of the capillary and critical crystallization pressure. This study provides physical insights about the variation mechanism of critical crystallization pressure for the square ice formation, and widespread applications in many fields such as nanomaterial, 42 nanofluidic, 42,43 and nanotribology. 44 ■ COMPUTATIONAL METHODS Molecular Dynamics Simulation.…”

Puckered Zigzag Monolayer Ice: Does a Confined Flat Four-Coordinated Monolayer Ice Always Have a Corresponding Puckered Phase?

“…Confined water is ubiquitous in nature and of central importance to a wide range of fields such as friction, nanofluidics, geoscience, and nanoscience. − The behavior of nanoconfined water may differ markedly from that of bulk water, , owing to perturbations induced by the interface. − In addition to temperature and pressure, the length scale of the confinement and the hydrophobicity of the surfaces play a key role in the properties of confined water, which include complex phase behavior, phase transitions, and anomalous self-diffusion. − For example, the pressure-driven flow rate of water through narrow-diameter carbon nanotubes exhibits anomalous transport behavior, and the confined water can form many novel phases. − …”