Abstract
Incoherent neutron scattering by water confined in carbon nanohorns was measured with the backscattering spectrometer SPHERES and analyzed in exemplary breadth and depth. Quasielastic spectra admit -plus-Kohlrausch fits over a wide and range. From the and dependence of fitted amplitudes and relaxation times, however, it becomes clear that the fits do not represent a uniform physical process, but that there is a crossover from localized motion at low to diffusive relaxation at high . The crossover temperature of about 210 to 230 K increases with decreasing wave number, which is incompatible with a thermodynamic strong-fragile transition. Extrapolated diffusion coefficients indicate that water motion is at room temperature about 2.5 times slower than in the bulk; in the supercooled state this factor becomes smaller. At even higher temperatures, where the spectrum is essentially flat, a few percentages of the total scattering go into a Lorentzian with a width of about , probably due to functional groups on the surface of the nanohorns.
7 More- Received 2 February 2015
- Revised 1 December 2015
DOI:https://doi.org/10.1103/PhysRevE.93.022104
©2016 American Physical Society