Study Of Carbon Nanotube/Graphene-Water Interaction: Molecular Dynamics Simulations

It is well known that carbon nanotube and graphene have excellent mechanical and electrical properties. The interaction between carbon nanotubes/graphene and water molecules is widely used in drug delivery, desalination, ion exchange and etc. We studied the interaction of carbon nanotube/graphene and water by molecular dynamics simulations. We found that the effect of curvature is crucial on the behaviors of confined water layers. We found droplets can cause the collapsion of carbon nanotubes. We also studied the effect of factors on the fusion process of two droplets at nanoscale. The thesis includes the following aspects:We found that the effect of curvature is crucial on the behaviors of confined water layers. We showed that the inter-wall space of the double-walled carbon nanotubes controlled the structure of water layers, by which the water formed monolayer, bilayer and triple-layer. We found that while the inter-wall space of the nanotubes regulates the diffusion of water along the axial direction of double-walled carbon nanotube, the curvature dominates the diffusion along the circumferential direction. This behavior led to an unusual anisotropic diffusion of water molecules. We also found that a curved confinement might help to trap the water molecules and thus induced phase transition to a 2D crystalline ice in the presence of electric field. These results uncover the importance of curvature in the confinement of water molecules, and shed valuable light on controlling the structure and dynamics of water molecules at nanoscale.We found droplets can enter into carbon nanotubes by capillary action, and carbon nanotubes may have a great deformation or even collapsion by surface tension.We calculated the critical buckling force of carbon nanotubes with different diameters and length through theoretical model analysis, molecular dynamics simulation and finite element method. We found the critical buckling force is proportional to the length and inversely proportional to the cubic of carbon nanotubes’ radius.We studied the fusion process of two droplets in nanoscale by molecular dynamics method. We studied the effect of distance of the droplets, contact angles, aspect ratio of the substrate, stiffness of substrate, curvature of substrate to the fusion time of two droplets. The results showed that small distance, large contact angle, small aspect ratio of substrate, low rigidity of substrate, positive curvature of substrate can significantly facilitate the fusion of droplets. In contrast, small distance, large contact angle, large aspect ratio of substrate, high rigidity of substrate, positive curvature of substrate can significantly promote the fusion of droplets.