Dynamics of water confined in single- and double-wall carbon nanotubes

Using high-resolution quasielastic neutron scattering, we investigated the temperature dependence of single-particle dynamics of water confined in single- and double-wall carbon nanotubes with the inner diameters of 14 +/- 1 and 16 +/- 3 angstrom, respectively. The temperature dependence of the alpha relaxation time for water in the 14 angstrom nanotubes measured on cooling down from 260 to 190 K exhibits a crossover at 218 K from a Vogel-Fulcher-Tammann law behavior to an Arrhenius law behavior, indicating a fragile-to-strong dynamic transition in the confined water. This transition may be associated with a structural transition from a high-temperature, low-density (< 1.02 g/cm(3)) liquid to a low-temperature, high-density (> 1.14 g/cm(3)) liquid found in molecular dynamics simulation at about 200 K. However, no such dynamic transition in the investigated temperature range of 240-195 K was detected for water in the 16 angstrom nanotubes. In the latter case, the dynamics of water simply follows a Vogel-Fulcher-Tammann law. This suggests that the fragile-to-strong crossover for water in the 16 angstrom nanotubes may be shifted to a lower temperature. (c) 2206 American Institute of Physics.