Paper title:

Capillary filling with giant liquid/solid slip: Dynamics of water uptake by carbon nanotubes

 

Journal:

J. Chem. Phys. 135, 214705 (2011)

 

Author/s:

Laurent Joly

LPMCN, Universit? de Lyon, UMR 5586 Universit? Lyon 1 et CNRS, F-69622 Villeurbanne, France

 

 

Summary:

The paper suggests a modification for the typical dynamics of capillary filling in which the effects of liquid/solid slip should be accounted for. First, the author derived the general equations for describing capillary filling with partial slip conditions. Afterwards, they focused on conditions where there is large slip, in this case, a system of carbon nanotube (CNT) which is reported to have large liquid/solid slip. Then, they did molecular dynamics (MD) simulations of water filling CNTs to show what factor limits the filling velocity. Finally, a modified model for full capillary filling was presented. This new model accounts for the entrance effects due to viscous dissipation.

For a CNT, the slip length is so much larger compared to the pore size. In this particular case, this study showed that only the friction coefficient of the liquid at the wall affects flow, and not the liquid viscosity. In addition, it was found that the capillary filling velocity doesn’t depend on the radius of the CNT.

The author used LAMMPS for the MD simulations, and VMD to visualize the system. The simulation system consists of a water box, bounded by two parallel graphene sheets on two sides. A CNT with a radius varying from 5.14 to 18.7 ? was connected perpendicular to the surface of one of the graphene sheets. Once the trapped water was equilibrated, this graphene sheet shall be removed to facilitate the capillary filling with water. The water model adapted was TIP3P and water-carbon interactions were modeled using Lennard-Jones potential between O and C atoms. The system was maintained at a constant temperature of 300K using the Nose-Hoover thermostat.

For this study, there is a special consideration about viscosity. Hence, for one part of the simulations the author needed to use the dissipative particle dynamics (DPD) thermostat provided by LAMMPS. This can preserve hydrodynamics and add pair-wise interactions between atoms with a dissipative force depending on the relative velocity and a random force following Gaussian statistics.

 

Contribution and application:

This paper has a very deep discussion about physic-chemical phenomena of capillary filling of water in CNT. This may not be necessary for our studies about desalination. However, what makes this paper valuable for our research is that the author was kind enough to provide the input scripts and simulation details that were used for the LAMMPS. These can be used by our lab to further learn how to simulate systems involving water, graphene, and CNT.

By: Hannah Ebro

hannah@gist.ac.kr