Square ice in graphene nanocapillaries.

Area of Science:

• Materials Science
• Nanotechnology
• Physical Chemistry

Background:

• Water exists in various bulk phases, including hexagonal ice, and also in low-dimensional forms adsorbed at interfaces or confined in pores.
• Confined water plays a crucial role in diverse scientific fields, but its experimental structural analysis remains challenging.
• Hydrophobic confinement is a key environment where unique water phases may form.

Purpose of the Study:

• To experimentally investigate the crystal structure of water confined within hydrophobic nanochannels.
• To characterize the phase and symmetry of nanoconfined water under ambient conditions.

Main Methods:

• High-resolution electron microscopy was employed to image water confined between two graphene sheets.
• Molecular dynamics simulations were conducted to support experimental observations and explore phase behavior.

Main Results:

• Observation of a novel ice phase, termed 'square ice,' formed by nanoconfined water at room temperature.
• Square ice exhibits a symmetry distinct from conventional ice, with a high packing density and a lattice constant of 2.83 Å.
• The phase can assemble into bilayer and trilayer crystallites and is predicted to be stable in various hydrophobic nanochannels.

Conclusions:

• The experimental imaging and simulations confirm the existence of square ice under hydrophobic confinement.
• This finding reveals a new fundamental phase of water, with significant implications for understanding water behavior in nanoscale environments.
• The discovery of square ice opens avenues for manipulating water properties in nanomaterials and related applications.