Anomalous dynamics of water confined in MCM-41 at different hydrations

We present the results of molecular dynamics simulations on water confined in a silica pore of 15 A modelled to mimic the MCM-41 structure. We focus on the dynamical properties of water for different hydration levels of the pore. Density profiles show a well-defined double-layer structure close to the surface. From the analysis of the layers we find that water molecules close to the substrate show an anomalous diffusion which is connected to the behaviour of the residence time distribution. The interaction with the substrate induces temporal disorder. As a consequence strong deviations are found from the Markovian processes that usually determine the long-time diffusion properties. The residence time distribution of the water molecules in the inner part of the pore, far from the hydrophilic surface, is compatible with a Markovian process.