Nonequilibrium molecular dynamics simulation for studying the effect of pressure difference and periodic boundary conditions on water transport through a CNT membrane

ABSTRACT

A NEMD simulation system is constructed to simulate at two-dimensional (2D) periodic boundary conditions (PBCs) and to create two different pressures on two sides of the carbon nanotube (CNT) membrane. The simulation results show that water permeation through the same CNT membrane driven by different pressure differences exhibit similar transport phenomenon including unusually fast water permeation and a periodic (non-parabolic) radial velocity distribution unlike the parabolic form characteristic of continuum flow in the CNT membrane. A three-dimensional (3D) PBC system is also constructed to simulate water permeation through the same CNT membrane at the same pressure differences, to show the effect of PBC and simulation methodologies on transport phenomenon. The two systems both show that the forward/backward water flux increases/decreases with increasing the pressure difference from 1.0 MPa to 8.0 MPa. However, the net flux is higher for the 3D PBC system, especially at higher pressure difference is high. In general, the NEMD simulation method using the 2D PBC system is shown to be a feasible and valuable tool for studying pressure-driven permeation processes such as nanofiltration through these studies with model CNT membrane.

KEYWORDS:

• NEMD
• water transport
• pressure difference
• PBC
• CNT membrane

Acknowledgments

The Natural Sciences and Engineering Research Council Canada (NSERC) and McMaster University are thanked for their financial support. The Shared Hierarchical Academic Research Computing Network (SHARCNET, http://www.sharcnet.ca) is gratefully acknowledged for providing high performance computing technology for this work. This work is also supported by the National Natural Science Foundation of China (No. 21406013).

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

National Natural Science Foundation of China [grant number 21406013]; Natural Sciences and Engineering Research Council Canada (NSERC); McMaster University.