(110d) On the Mechanism of Water Diffusion in Narrow Carbon Nanotubes | AIChE

(110d) On the Mechanism of Water Diffusion in Narrow Carbon Nanotubes

Authors 

Striolo, A. - Presenter, The University of Oklahoma


Carbon nanotubes show exceptional physical properties that render them promising candidates as building blocks for nano-structured materials. Many ambitious applications, ranging from gene therapy to membrane separations, require the delivery of fluids, in particular aqueous solutions, through the interior of carbon nanotubes. To foster these and other applications, it is necessary to understand the thermodynamic and transport properties of water confined within long narrow carbon nanotubes. Previous theoretical work considered either short carbon nanotubes or short periods of time. We report on molecular dynamics simulations for water confined in infinitely-long carbon nanotubes of diameter 1.08 nm. We consider pristine carbon nanotubes as well as carbon nanotubes doped with a few oxygenated sites, modeled as carbonyl groups. Our results indicate that water molecules confined within pristine carbon nanotubes diffuse through a fast ballistic motion mechanism for up to 500 ps at room temperature. The presence of a few oxygenated sites significantly slows the diffusion of confined water. When only a few water molecules are considered, the diffusion mechanism appears of the single-file type for extended periods of time. We argue that this result is a consequence of both the narrow diameter of the carbon nanotubes considered and of the attractive interactions between the carbonyl groups and the confined water molecules. Our calculations also show that when the carbon nanotubes are filled with confined water the diffusion mechanism observed within pristine or doped carbon nanotubes does not differ significantly, probably because of the small amount of oxygenated sites considered in our simulations. Our results are important for designing nano-fluidic apparatuses to develop, for example, novel drug-delivery devices.