The effect of the topology of single-walled carbon nanotubes upon the diffusion dynamics of water confined in armchair and zig-zag nanotubes was investigated. It was found that the activation energy for molecular diffusion in zig-zag nanotubes was greater than that in armchair nanotubes of similar diameter. This led to water molecules in zig-zag nanotubes diffusing much slower than in armchair nanotubes. Further calculations of the potential energy surfaces of water in these two types of nanotube explained the mechanism of diffusion dynamics of confined water. This showed that the topology of potential energy surfaces inside nanotubes could control the diffusion behaviors of water within them. Since the topology of potential energy surfaces within nanotubes could be modified by using various chemical and/or physical methods, these results indicated the possibility of controlling the diffusion behavior within nanotubes by molecular engineering; without changing the pore size.

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