The effect of topology of single-walled carbon nanotubes upon the diffusion dynamics of water confined in armchair and zig-zag carbon nanotubes was investigated (figure 1). It was found that the activation energy of molecular diffusion in zig-zag carbon nanotubes was greater than that in armchair ones at similar diameters, which led to water molecules in zig-zag carbon nanotube diffusing much slower than in armchair carbon nanotubes. Further calculations of the potential energy surfaces of water in these two types of carbon nanotube explained the mechanism of diffusion dynamics of confined water. This research showed that the topology of potential energy surfaces within a carbon nanotube could control the diffusion behavior of water inside it. Since the topology of potential energy surfaces inside carbon nanotubes could be modified by various chemical and/or physical methods, this work indicated the possibility of controlling the diffusion behavior inside the carbon nanotubes by molecular engineering, without changing its pore size.

Diffusion Dynamics of Water Controlled by Topology of Potential Energy Surface inside Carbon Nanotubes. Liu, Y.C., Shen, J.W., Gubbins, K.E., Moore, J.D., Wu, T., Wang, Q.: Physical Review B, 2008, 77[12], 125438