Simulation of water impregnation through vertically aligned CNT forests using a molecular dynamics method.

Yoshinobu Shimamura,Tomohiro Tajiri,Ryosuke Matsuzaki

doi:10.1038/srep32262

Yoshinobu Shimamura, Tomohiro Tajiri + Show 1 more

Open Access

https://doi.org/10.1038/srep32262

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Abstract

The flow rate of water through carbon nanotube (CNT) membranes is considerably large. Hence, CNT membranes can be used in nanofluidic applications. In this work, we performed a molecular dynamics (MD) simulation of the introduction of water into CNTs in the CNT membranes, especially in vertically aligned CNT forests. The results showed that the Knudsen number (Kn) increased with an increasing volume fraction of CNT (VC) and was greater than 10−3 for each VC. Beyond this value, the flow became a slip flow. Further, the permeability increased as VC increased in the actual state calculated by the MD simulation, whereas the permeability in the no-slip state predicted by the Hagen–Poiseuille relationship decreased. Thus, a clear divergence in the permeability trend existed between the states. Finally, the flow enhancement ranged from 0.1 to 23,800, and the results show that water easily permeates as VC increases.

Highlights

Carbon nanotubes (CNTs) possess many excellent characteristics such as high thermal conductance, high strength, and chemical stability
We present our results in the following aspects: (1) investigation of the Knudsen number (Kn), (2) verification of the application of permeability predicted by a no-slip state, and (3) investigation of the divergence between the permeability in the slip and actual states by calculating the flow enhancement in a nanopore
We established a sufficiently long distance with respect to the CNT axis so that the model duplicated in each direction does not affect the water www.nature.com/scientificreports/

Summary

Introduction

Carbon nanotubes (CNTs) possess many excellent characteristics such as high thermal conductance, high strength, and chemical stability. The flow rates of water through a CNT have been reported to be from one to five orders of magnitude greater than those predicted by the continuum-based no-slip Hagen–Poiseuille relationship. These flow rates increase as the area of the permeation region decreases. Analytical and experimental flow investigations inside a CNT have been performed, no analytical investigations have been conducted outside a CNT in a VACNF. Equation by comparing the permeabilities of the Gebart equation (no-slip state) (derived using a hypothesizing Hagen–Poiseuille flow) with those in an actual state that uses molecular dynamics (MD) results and to verify the flow tendency in a nanopore. We present our results in the following aspects: (1) investigation of the Knudsen number (Kn), (2) verification of the application of permeability predicted by a no-slip state, and (3) investigation of the divergence between the permeability in the slip and actual states by calculating the flow enhancement in a nanopore

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Results

Conclusion