Experimental evidence of a liquid-liquid transition in interfacial water

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. 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 liquid water in this very interesting temperature range between 150 and 235 K. We present nanosecond-time-scale measurements of local rotational and translational dynamics of interfacial, non-crystalline, water from 77 to 280 K. These experimental dynamic results are combined with calorimetric and diffraction data to show that after exhibiting a glass transition at 165 K, interfacial water experiences a first-order liquid-liquid transition at 240K from a low-density to a high-density liquid. This is the first direct evidence of the existence of a liquid-liquid transition involving water.