Observation of a dynamic crossover in water confined in double-wall carbon nanotubes

High-resolution quasielastic neutron scattering spectroscopy was used to measure H2O hydrated double-wall carbon nanotubes (DWNT). The measurements were made at a series of temperatures from 250 K down to 150 K. The relaxing-cage model was used to analyze the quasielastic spectra. We observed clear evidence of a fragile-to-strong dynamic crossover (FSC) at T(L) = 190 K in the confined water. We further show that the mean-square atomic displacement of the hydrogen atoms in water exhibits a sharp change in slope at approximately the same temperature 190 K. Comparing the result with that obtained from the confined water in hydrophilic porous silica material MCM-41, we demonstrate experimentally that water confined in a hydrophobic substrate exhibits a lower dynamic crossover temperature by deltaT(L) approximately = 35 K.