Water at nanoscale confined in single-walled carbon nanotubes studied by NMRS. Ghosh1, K. V. Ramanathan2 and A. K. Sood1
1 Department of Physics, Indian Institute of Science - Bangalore 560 012, India
2 Sophisticated Instruments Facility, Indian Institute of Science Bangalore 560 012, India
(Received 18 September 2003; accepted in final form 11 December 2003)
Proton NMR studies have been carried out as a function of temperature from 210 to 300 on water confined within single-walled carbon nanotubes. The NMR lineshape at and below the freezing point of bulk water is asymmetric and can be decomposed into a sum of two Lorentzians. The intensities of both the components decrease with the lowering of the temperature below 273 , one component, L1, vanishing below 242 and the other component, L2, below 217 . Following the simulations of Koga et al. showing that the radial density profile of confined water in single-wall carbon nanotubes has a distribution peak at the center which disappears below the freezing temperature, the L1-component is associated with the protons of the water molecules at the center and the L2-component is associated with protons of water molecules at a distance of from the walls of the nanotubes. In this scenario the complete freezing of the water at is preceded by the withdrawal of the water molecules from the center.
61.46.+w - Nanoscale materials: clusters, nanoparticles, nanotubes, and nanocrystals.
87.64.Hd - EPR and NMR spectroscopy.
82.60.Nh - Thermodynamics of nucleation.
© EDP Sciences 2004