Researchers in Japan have unveiled a remarkable discovery about water, revealing that it can exist in a state that is both solid and liquid simultaneously. This phenomenon occurs when water molecules are confined within extremely narrow spaces, leading to behaviors that challenge conventional understanding of this essential liquid.
The newly identified state, termed the premelting state, showcases a unique interaction among water molecules. In ice, the molecules are rigidly structured, while in liquid water, they move freely. In the premelting state, water molecules maintain a fixed position, akin to ice, yet they also exhibit rapid spinning similar to that of liquid water. This dual behavior was documented in a study led by Makoto Tadokoro, a chemist at the Tokyo University of Science.
Tadokoro explained, “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.” This intricate balance between solidity and liquidity highlights the complex nature of water at a molecular level.
To observe this phenomenon, the researchers utilized a sophisticated experimental setup. Instead of regular water, they employed ‘heavy water,’ where the hydrogen atoms are replaced by deuterium, an isotope that includes a neutron in its nucleus. Dubbed D2O, this heavy water was confined within rod-shaped crystals featuring hydrophilic channels measuring just 1.6 nanometers in width.
The research team gradually warmed the frozen D2O while employing static solid-state deuterium nuclear magnetic resonance (NMR) spectroscopy to monitor the changes. This approach unveiled a hierarchical three-layered structure within the confined water, where different types of molecular movements and interactions occurred in each layer.
The premelting state is reminiscent of a thin film of water that can form on the surface of ice, even under sub-freezing temperatures. However, the behavior of water in bulk ice differs significantly from what occurs under extreme confinement.
Water has long been known to exhibit unusual properties at the nanoscale. For instance, its electrical characteristics can vary dramatically, and it can become ‘unfreezable’ at near absolute zero temperatures or freeze solid even when conditions suggest it should boil. These unique behaviors open doors to potential practical applications, according to the research team.
By exploring new ice network structures, there may be opportunities to enhance the storage of energetic gases such as hydrogen and methane. Additionally, this research could pave the way for developing innovative water-based materials, including artificial gas hydrates.
The findings of this groundbreaking study were published in the Journal of the American Chemical Society, shedding light on the peculiar nature of water and its myriad states.
