Structural and dynamical properties of water confined in carbon nanotubes

Leandro Barros Da Silva

doi:10.1007/s40097-014-0104-3

Abstract

Structural and dynamical properties of water confined in carbon nanotubes are investigated by classical molecular dynamics simulations. It is found that density and self-diffusion coefficients of water depend on the diameter of confinant nanotube and exhibit anomalous behavior in narrow tubes. It is shown that water forms several different orderings inside the nanotube channel and these arrangements impact on the energetics of hydrogen bonds. Considering the relationship between the geometry of hydrogen bonds and their energetics, a discussion on the dynamics of enclosed water is presented.

Highlights

Water is a complex fluid, necessary for life and present in most everyday human activity [1]
It can be seen that the water density is strongly dependent on the CNT diameter in narrower nanotubes, what can be attributed to the different arrangements observed for water molecules inside these nanotubes
This molecular dynamics study showed that water has physical and dynamical properties largely modified when confined into small diameter carbon nanotubes

Summary

Introduction

Water is a complex fluid, necessary for life and present in most everyday human activity [1]. When confined in nanopores or nanochannels its behavior become even more intriguing: it experiences a liquid–solid transition at room temperature [2] and presents large size-dependent viscosity [3] and thermal conductivity [4], among other properties. Hundreds of studies have focused on the remarkable fast diffusion properties of water in nanochannels, with. The notable physical characteristics of confined water are naturally related to the dynamics of the hydrogen bonds (HB) formed between the water molecules in the nanochannels. The energetics of an HB is much influenced by the relative orientation between each pair of molecules, in a way that any modification in this character has a profound impact on the dynamics of the bond [6]. Pascal and collaborators [2] showed that the free energy variation of water when it fills the CNT cavity from a bulk reservoir is due to (1) entropical gain in sub-nanometer tubes or (2) enthalpic loss in larger CNTs

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