Molecular Dynamics Simulation Study of the Structural Characteristics of Water Molecules Confined in Functionalized Carbon Nanotubes

Abstract

Molecular dynamics (MD) simulations were performed to study the structural properties of water molecules confined in functionalized carbon nanotubes (CNTs). Four CNTs, two armchair-type (6, 6), (7, 7) and two zigzag-type (10, 0), (12, 0) CNTs, representing different helicities and different diameters, were chosen and functionalized at their open ends by the hydrophilic -COOH and the hydrophobic -CH 3 groups. The structural properties of water molecules inside the functionalized CNTs, including the orientation distributions of dipole moment and O-H bonds, the length of the single-file water chain, and the average number of hydrogen bonds, were analyzed during a process of simulations. MD simulation results in this work showed that the -CH 3 functional groups exert little special effects on the structural properties of water molecules. It is mainly due to the relatively small size of the -CH 3 group and its hydrophobic nature, which is consistent with hydrophobic CNTs. For CNTs functionalized by -COOH groups, the configurations of -COOH groups, incurvature or excurvature, determine whether water molecules can enter the CNTs. The incurvature or excurvature configurations of -COOH groups are the results of synergy effects of the CNTs' helicity and diameter and control the flow direction of water molecules in CNTs.

Diffusion of water molecules confined in slits of rutile TiO2(110) and graphite(0001)

“…Although a few theoretical works on TiO 2 are related to water [15][16][17][18], few have been focused on the diffusion of water confined in TiO 2 slits. Our previous works of molecular dynamics (MD) showed that the chemical modification of carbon nanotubes would affect the water behaviors [19][20][21][22][23]. It means that the chemical property of the solid surface plays an important role in the structural behaviors of confined water, and will accordingly influence their diffusion behavior.…”

Self-diffusivity, hydrogen bonding and density of different water models in carbon nanotubes

“…A key step for this novel nanomedicine technology consists in delivering small amounts of aqueous solutions through the hollow interior of CNTs. When water is confined within small nanotubes, however, its properties, structure and dynamics change dramatically and differ considerably from those of bulk (see for instance [3,4,5,6,7]). The goal of this work is to use molecular dynamics for gaining further insights into some of the properties of water confined in CNTs.…”

Intelligent energy dissipation capability of CNTs based nanofluid

“…Cambre´et al [11] also observed the confined water CNTs directly by using Raman spectra and experimentally demonstrated the phenomenon of single-file transport of water into CNTs, which was firstly reported by Hummer et al [12]. Huang et al [13] used MD simulations to study the structural properties of water molecules confined in functionalized CNTs and found that the -CH 3 functional groups exert little special effects on the structural properties of water molecules while the configurations of -COOH groups, incurvature or excurvature, determine whether water molecules can enter the CNTs. both CF 4 plasma treating and fluorosilane grafting methods are performed to functionalize the CNTs.…”