Europhys. Lett.
Volume 65, Number 5, March 2004
Page(s) 678 - 684
Section Condensed matter: structure, mechanical and thermal properties
Published online 01 February 2004
Europhys. Lett., 65 (5) , pp. 678-684 (2004)
DOI: 10.1209/epl/i2003-10160-9

Water at nanoscale confined in single-walled carbon nanotubes studied by NMR

S. 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 $\un{K}$ to 300 $\un{K}$ 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 $\un{K}$, one component, L1, vanishing below 242 $\un{K}$ and the other component, L2, below 217 $\un{K}$. 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 $\sim 3$ $\un{\AA}$ from the walls of the nanotubes. In this scenario the complete freezing of the water at $\sim
212$ $\un{K}$ 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