Suppression of the dynamic transition in surface water at low hydration levels: a study of water on rutile.

Our quasielastic neutron-scattering experiments and molecular-dynamics simulations probing surface water on rutile (TiO2) have demonstrated that a sufficiently high hydration level is a prerequisite for the temperature-dependent crossover in the nanosecond dynamics of hydration water. Below the monolayer coverage of mobile surface water, a weak temperature dependence of the relaxation times with no apparent crossover is observed. We associate the dynamic crossover with interlayer jumps of the mobile water molecules, which become possible only at a sufficiently high hydration level.