Abstract
Water continually generates vast research interest due to its many unusual properties, not least of which it’s behaviour when confined in small spaces. Understanding this behaviour has applications in such fields as construction, medicine and desalination. The discovery of carbon nanotubes has lead to significant research output into their potential applications. Carbon nanotubes are known to exhibit valuable properties including high tensile strength and good thermal and electrical conductivity. The methods for synthesising carbon nanotubes are improving and it will soon be possible to grow aligned tubes of specific and uniform diameters. Such advancements will make it possible to consider their use in applications such as nano-needles and filtration devices like desalination membranes. This work uses molecular dynamics simulations to examine the flow characteristics of water confined within carbon nanotubes of diameters ranging from 0.71nm to 1.43nm. Different initial water bath pressures and temperatures have been investigated. Flow rates in all cases have been found to well exceed those predicted by the classical Hagen-Poiseuille relation and it is postulated that changes in viscosity and slip length need to be included to bring the predicted flows more in line with those observed from simulation. The confined water molecules have been shown to undergo re-structuring, the nature of which is strongly diameter dependent. This structuring appears to give rise to an ‘optimum flow’ in the case of the 1.19nm nanotube, which exhibits higher flowrates than its larger counterpart.