Supercooled confined water and the mode coupling scenario

Studies of single particle dynamics of water confined in silica pores performed with computer molecular dynamics and inelastic neutron scattering are presented. In the computer study for the highest hydrations two dynamical regimes are found: close to the hydrophilic substrate molecules are below the mode coupling crossover temperature, T-C, already at ambient temperature (bound water). The water closer to the center of the pore (free water) approaches T-C upon supercooling as predicted by mode coupling theories. Inelastic neutron scattering data are analyzed upon supercooling for hydration levels of 12% and 8%. Also these data are discussed in the framework of the mode coupling theory, in the region of the beta relaxation. Strong deviations from the theoretical predictions are found and ascribed to the existence of a low-frequency scattering excess also visible in the simulation. (C) 2002 Elsevier Science B.V. All rights reserved.