Abstract
Carbon materials have unveiled outstanding properties as membranes for water transport, both in 1D carbon nanotube and between 2D graphene layers. In the ultimate confinement, water properties however strongly deviate from the continuum, showing exotic properties with numerous counterparts in fields ranging from nanotribology to biology. Here, by means of molecular dynamics, we show a self-organized inhomogeneous structure of water confined between graphene sheets, whereby the very strong localization of water defeats the energy cost for bending the graphene sheets. This leads to a two-dimensional water droplet accompanied by localized graphene ripples, which we call “dripplon.” Additional osmotic effects originating in dissolved impurities are shown to further stabilize the dripplon. Our analysis also reveals a counterintuitive superfast dynamics of the dripplons, comparable to that of individual water molecules. They move like a (nano-) ruck in a rug, with water molecules and carbon atoms exchanging rapidly across the dripplon interface.
Highlights
Carbon materials have unveiled outstanding properties as membranes for water transport, both in 1D carbon nanotube and between 2D graphene layers
We investigate a peculiar inhomogeneity caused by the coupling mentioned above in a two-dimensional water thin film confined between graphene sheets, revealed using molecular dynamics (MD) simulations
When the density of water molecules contained between the graphene sheets exceeds a threshold, a two-dimensional droplet of localized water is formed by bending the graphene sheets—here we call this droplet “dripplon.” It has recently been shown that an isolated water droplet maintains its localized structures between two graphene sheets against the elasticity[39]
Summary
Carbon materials have unveiled outstanding properties as membranes for water transport, both in 1D carbon nanotube and between 2D graphene layers. We propose below a detailed understanding for the creation of this structure, coupling calculation of the free energy and disjoining pressure of mono- and bi-layers of water, together with a thermodynamic elasto-capillary modelization.
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