Uncertainties in the Capillary Filling of Heterogeneous Water Nanochannels
F Ramazani and F Ebrahimi, JOURNAL OF PHYSICAL CHEMISTRY C, 120, 12871-12878 (2016).
The phenomenon of water filling of heterogeneous nanocapillaries composed of hydrophilic and hydrophobic zones is studied by molecular dynamics simulation. The heterogeneous nanocapillaries have been constructed by reducing the strength of Lennard-Jones (LJ) interaction between oxygen and wall atoms in certain. domains of otherwise pristine carbon nanotubes. The modified or reduced LJ interaction is tuned to a value that corresponds to the hydrophobic characteristics. Nanochannels of different radii and lengths in which up to 50% of atoms had hydrophobic interactions have been investigated. Our simulations show that carbon nanotubes (CNTs) with a small hydrophobic zone within will eventually be invaded by water; however, the existence of a small hydrophobic region in the tube entrance might interrupt the flow of water molecules for an unknown time interval. This retardation time is found to be a random variable, sometimes magnitudes larger than the filling time of a pristine CNT. When the nanotube consists of alternate hydrophilic and hydrophobic blocks of equal size, water occupancy progresses between filled and partially filled states or shows. filling/emptying transitions, depending on the size of the nanotube and the extent of the hydrophobic zones. The uncertainty in the retardation time still remains when the wall atoms next to the entrance have the hydrophobic characteristic.
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