The headers will be insert by the Publisher The headers will be insert by the Publisher The headers will be insert by the Publisher Phase transitions of interfacial water at 165 and 240K. Connections to bulk water physics and protein dynamics. J.-M. Zanotti 1 , M.C. Bellissent-Funel 1 and A.I. Kolesnikov 2 1 Laboratoire Léon Brillouin (CEA-CNRS), CEA Saclay, 91191 Gif-sur-Yvette Cedex, France 2 IPNS, Argonne National Laboratory, Argonne, IL 60439, USA Abstract. We are considering water adsorbed as a monolayer on Vycor, a porous silica glass. The interfacial water molecules interact with the substrate through hydrogen bonding with the numerous silanol (Si-OH) groups present all over the surface. This special form of water exhibits peculiar dynamical properties. A combined calorimetric, diffraction, high resolution quasi-elastic and inelastic neutron scattering study shows that interfacial water experiences a glass transition at 165 K and a liquid-liquid transition at 240 K from a low-density to a high density-liquid. We show that this unusual behaviour, compared to the bulk, is due to a strong weakening of the hydrogen-bond strength, possibly due to the reduced number of hydrogen-bonds engaged by water molecules when they are in an interfacial two dimensional situation. The connections of these findings to the physics of bulk water and protein dynamics are discussed. 1. INTRODUCTION At ambient pressure, bulk liquid water shows an anomalous increase of thermodynamic quantities and apparent divergences of dynamic properties on approaching a temperature T s of 228 K. Among the different scenarios proposed to explain this behaviour at T s , the existence of a second critical point has been proposed [1]. Unfortunately, at normal pressure, supercooled water spontaneously freezes below the homogeneous nucleation temperature, T H = 235 K. Upon heating, the two forms of Amorphous Solid Water (ASW), LDA (Low Density Amorphous Ice) and HDA (High Density Amorphous Ice), crystallise above T X = 150 K. As a consequence, up to now no experiment has been able to explore the properties of bulk liquid water in this very interesting temperature range between 150 and 235 K, the so-called “no man’s land”. 2. EXPERIMENTAL 2.1 Sample preparation In this study, water is adsorbed as a monolayer on Vycor (Vycor brand porous glass n° 7930 is a product of Corning Glass Works), a porous hydrophilic silica glass. A partially hydrated sample was prepared by absorption of water in the vapour phase, until a level of hydration corresponding to a monolayer coverage was obtained.