Unique phase of water revealed in nanoscale confinement

Unique phase of water revealed in nanoscale confinement
by Riko Seibo
Tokyo, Japan (SPX) Sep 25, 2025

Despite being one of the most studied substances on Earth, water continues to surprise scientists with unexplored behaviors. Researchers at Tokyo University of Science have now uncovered new details of how water behaves in extreme confinement, providing the clearest evidence yet of a mysterious "premelting" phase that blurs the line between solid and liquid.

The team, led by Professor Makoto Tadokoro with Lecturer Fumiya Kobayashi and PhD student Tomoya Namiki, used static solid-state deuterium nuclear magnetic resonance (NMR) spectroscopy to investigate heavy water confined inside hydrophilic nanopores of specially designed molecular crystals. Their results, published in the Journal of the American Chemical Society on August 27, 2025, revealed a hierarchical, three-layered arrangement of water molecules that organize differently from bulk ice.

Within channels just 1.6 nanometers wide, the water formed distinct layers with unique hydrogen-bonding patterns and molecular motions. As the crystals were gradually heated, the researchers observed a new transition phase where incompletely bonded water molecules began to melt while adjacent layers remained frozen. This produced the elusive premelting state, where solid-like positional order coexisted with liquid-like rotational mobility.

Measurements of spin-lattice relaxation times showed that while confined molecules stayed relatively fixed in position, their rotational motion was comparable to liquid water. "The premelting state involves the melting of incompletely hydrogen-bonded H2O before the completely frozen ice structure starts melting during the heating process. It essentially constitutes a novel phase of water in which frozen H2O layers and slowly moving H2O coexist," explained Prof. Tadokoro.

The findings offer a critical step toward understanding confined water dynamics, which influence natural systems such as ion transport through cell membranes and engineered systems like nanofluidic devices. Beyond basic science, the work could open practical avenues, such as engineering new ice network structures for storing energy-rich gases like hydrogen and methane or developing artificial gas hydrates.

Research Report:Solid-State 2H NMR Analysis for Hierarchical Water Clusters Confined to Quasi-One-Dimensional Molecular Nanoporous Crystals