Molecular dynamics simulations of functionalized carbon nanotubes in water: Effects of type and position of functional groups

Abstract

In this work the behavior of the (8,2) single walled carbon nanotubes (CNTs) and functionalized carbon nanotubes (FCNTs) with four functional groups in water were studied using molecular dynamic (MD) simulation method. Glutamine as a long chain functional group and carboxyl as a short chain functional group have been used as functional groups in FCNTs. Four functional groups in each FCNT were localized at two positions: (i) all four functional groups were in the sidewalls of nanotube, (ii) two functional groups were at the ends and two functional groups were in the sidewalls of nanotube. The intermolecular interaction energies between CNTs or FCNTs and water molecules, the plots of radial distribution function and the diffusion coefficients of CNTs and FCNTs in water were computed for investigating the effects of type and position of functional groups on the behavior of FCNTs in water. The obtained results from three methods are consistent with each others. Results showed that the position of the functional groups in FCNTs has an important role in the interaction of hydrophilic groups of FCNTs with water molecules. Furthermore we also investigated the behavior of FCNTs with sixteen carboxyl functional groups in water. The presence of these large numbers of carboxyl functional groups on the carbon nanotubes prevents water molecules from moving towards hydrophilic carboxyl functional groups. This demonstrates the advantage of using lower number of functional groups each containing many hydrophilic groups like glutamine functional group.