Exploring the Anomalous Phase Behavior of High-Pressure Ices in Diamond Confinement

Gao

et al. 2020

J. Phys. Chem. Lett.

Although computational prediction of new ice phases is a niche field in water science, the scientific subject itself is representative of two important areas in physical chemistry, namely, statistical thermodynamics and molecular simulations. The prediction of a variety of novel ice phases has also attracted general public interest since the 1980s. In particular, the prediction of low-dimensional ice phases has gained momentum since the confirmation of a number of low-dimensional “computer ice” phases in the laboratory over the past decade. In this Perspective, the research advancements in computational prediction of novel ice phases over the past few years are reviewed. Particular attention is placed on new ice phases whose physical properties or dimensional structures are distinctly different from conventional bulk ices. Specific topics include the (i) formation of superionic ices, (ii) electrofreezing of water under high pressure and in a high external electric field, (iii) prediction of low-density porous ice at strongly negative pressure, (iv) ab initio computational study of two-dimensional (2D) ice under nanoscale confinement, and (v) 2D ices formed on a solid surface near ambient temperature without nanoscale confinement. Clearly, the formation of most of these novel ice phases demands certain extreme conditions. Ongoing challenges and new opportunities for predicting new ice phases from either classical molecular dynamics simulation or high-level ab initio computation are discussed.

mentioning

confidence: 99%

Computational Prediction of Novel Ice Phases: A Perspective

Gao

et al. 2020

J. Phys. Chem. Lett.

“…Water tends to assemble in layers in the vicinity of interfaces in the bulk phase , and also in confinement. − These layered structures can be arranged in the form of monolayers, bilayers, trilayers, tetralayers, etc. depending on the confinement conditions or interface properties.…”

Section: Resultsmentioning

confidence: 99%

“…Such glass transitions are fundamentally distinct from liquid-to-solid state phase transitions in nanoconfined pure water. Pure water in quasi-two-dimensional confinement (by both graphitic and diamond walls) forms a variety of ordered structures, with a characteristic long-range order.…”

Section: Resultsmentioning

confidence: 99%

“…In this work, we prepared a simulation system inspired by similar quasi-two-dimensional systems in the literature, , wherein a pair of diamond sheets separated by a tunable gap width is flanked by two liquid reservoirs. Figure depicts this simulation setup.…”

Section: Computational Detailsmentioning

confidence: 99%

“…In the past few decades, there has been a surge of scientific interest in the phase behavior of salt-water under high pressure, bolstered by the conjectured existence of high-pressure ice polymorphs in the interior of planetary bodies with subsurface salty oceans. − The first naturally occurring ice VII on the Earth was recently discovered in diamond inclusions, wherein significant amounts of sodium and potassium hydrates were found . The formation and structures of ion-doped bulk ices, whose lattices incorporate trapped ionic species, have also been extensively studied using both simulations and experiments. − From a technological perspective as well, understanding the phase behavior of the salt-water system is crucial to various fields, including water desalination, , supercapacitors, − and biological applications. , There are currently 20 experimentally confirmed bulk crystalline ice phases, and strong confinement can induce even greater structural diversity. − Although tetrahedral coordination is favored in bulk water, confinement can contort the hydrogen-bonding network (HBN) into drastically different ordered structures. , Concomitantly, ions in confinement also exhibit properties which deviate from their bulk counterparts. − …”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Salt-Water System under Diamond Confinement

2021

Self Cite

Deriving inspiration from the salinity of ice VII inclusions in excavated diamonds, we explore the phase behavior of quasi-two-dimensional salt water in diamond nanoconfinement via molecular dynamics simulations. We construct the compression-limit phase diagram for several slit widths over a wide range of gigapascal-high lateral pressures. We observe the assembly of solid-like amorphous monolayer, bilayer, and trilayer phases, distinct from the ordered structures found in both pure bulk water and quasi-two-dimensional confined water. The underlying mechanism of dehydration, caused by the disruptive presence of ions, and the concomitant destruction of the long-range order of the encapsulating water hydrogen-bond network are critically analyzed. Orientational analyses of the constrained salt-water system reveal ties to interlayer water hydrogen bonding and the preferential arrangement of ion and water layers. Our results offer fresh insight into the formation and structural characteristics of the phases exhibited by nanoconfined salt water.

Dielectric Profile and Electromelting of a Monolayer of Water Confined in Graphene Slit Pore

et al. 2021

A monolayer of water confined between two parallel graphene sheets exists in many different phases and exhibits fascinating dielectric properties that have been studied in experiments. In this work, we use molecular dynamics simulations to study how the dielectric properties of a confined monolayer of water is affected by its structure. We consider six of the popular nonpolarizable water modelsSPC/E, SPC/Fw, TIP3P, TIP3P_M (modified), TIP4P-2005, and TIP4P-2005fand find that the in-plane structure of the water molecules at ambient temperature and pressure is strongly dependent on the water model: all the 3-point water models considered here show square ice formation, whereas no such structural ordering is observed for the 4-point water models. This allows us to investigate the role of the in-plane structure of the water monolayer on its dielectric profile. Our simulations show an anomalous perpendicular dielectric constant compared to the bulk, and the models that do not exhibit ice formation show very different dielectric response along the channel width compared to models that exhibit square ice formation. We also demonstrate the occurrence of electromelting of the in-plane ordered water under the application of a perpendicular electric field and find that the critical field for electromelting strongly depends on the water model. Together, we have shown the dependence of confined water properties on the different water structures that it may take when sandwiched between bilayer graphene. These remarkable properties of confined water can be exploited in various nanofluidic devices, artificial ion channels, and molecular sieving.