Existence of Multiple Phases of Water at Nanotube Interfaces

AB Farimani and NR Aluru, JOURNAL OF PHYSICAL CHEMISTRY C, 120, 23763-23771 (2016).

DOI: 10.1021/acs.jpcc.6b06156

Water, because of its anomalous properties, can exhibit complex behavior under strong confinement. At room temperature and pressure, water is assumed to exist in a single phase as a liquid under confinement (e.g., in a carbon nanotube). In this study, using extensive molecular dynamics simulations, we show the existence of multiple phases of water when water meets a nanotube surface under atmospheric conditions (T = 300 K, P = 1 atm). Vapor, high-density ice, and liquid water phases coexist in the region within similar to 1 nm from the surface. Structure factor, entropy, pressure, viscosity, and rotational diffusion of water layers near the surface reveal substantial phase anomalies induced by confinement. We show the presence of a new high-density solid-state ice layer (rho = 3.9 g/cm(3)) with rhombic structure coexisting adjacent to vapor and liquid water. The existence of multiple phases of water near an interface can explain, for example, the slip phenomena, self-filling behavior of a carbon nanotube, and fast transport of water.

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