Double dynamical regime of confined water

The Van Hove self correlation function of water confined in a silica pore is calculated from Molecular Dynamics trajectories upon supercooling. At long time in the $\alpha$ relaxation region we found that the behaviour of the real space time dependent correlators can be decomposed in a very slow, almost frozen, dynamics due to the bound water close to the substrate and a faster dynamics of the free water which resides far from the confining surface. For free water we confirm the evidences of an approach to a crossover mode coupling transition, previously found in Q space. In the short time region we found that the two dynamical regimes are overimposed and cannot be distinguished. This shows that the interplay between the slower and the faster dynamics emerges in going from early times to the $\alpha$ relaxation region, where a layer analysis of the dynamical properties can be performed.Comment: 6 pages with 9 figures. RevTeX. Accepted for pulbication in J. Phys. Cond. Mat

Dynamic properties of water in porous Vycor glass studied by dielectric techniques

The structure and dynamic properties of water in porous Vycor glass of 40 Å mean pore diameter, as well as their changes with temperature, were studied by dielectric relaxation spectroscopy and dc conductivity measurements. The mobility of water moledules in the pores was reduced compared with that of bulk water by a factor which decreased with increasing water content. A significant fraction of water in the first monolayer is transformed to a glassy state at about 170 K. The formation of water clusters around primary hydration sites started at about 0.02 g(H2O)/g (dry sample) where a transition to long-range connectivity amiong ater molecules was observed. © 1994