Molecular dynamics simulation of single-walled silicon carbide nanotubes immersed in water.

The structure and dynamics of water confined in single-walled silicon carbon nanotubes (SWSiCNTs) are investigated using molecular dynamics (MD) simulations. The density of water inside SWSiCNTs is reported, and an equation is suggested to predict the density of water inside SWSiCNTs. Interestingly, the water diffusion coefficients (D) here are larger compared with those in SWCNTs and single-walled boron-nitride nanotubes (SWBNNTs). Furthermore, water inside zigzag SWCNTs has a lower diffusion coefficient than water inside armchair SWCNTs. A thorough analysis of the density profiles, hydrogen bonding, and water molecule orientation inside SWSiCNTs is presented to explore the mechanism behind the diffusive behavior of water observed here. It is shown here, by mean square displacement (MSD) analysis, that water molecules inside SWSiCNTs diffuse with a ballistic motion mechanism for up to 500ps. Additionally it is confirmed here for the first time that water molecules confined in the SWSiCNTs with diameters of less than 10Å obey the single-file diffusion mechanism at time scales in excess of 500ps. The orientation of water molecules inside SWSiCNTs could be a good explanation for the difference between the diffusion coefficient in (6,6) and (10,0) SWSiCNTs. Finally, a PMF analysis explains the difficulty of water entrance into SWSiCNTs and also the different water self-diffusion inside armchair and zigzag SWSiCNTs. These results are motivating reasons to use SWSiCNTs in nanoscale biochannels, for instance, in drug-delivery applications.