“Similarities” between confined and supercooled water,

Neutron diffraction and deep inelastic neutron scattering experiments performed on bulk stable and supercooled water are compared with the same experiments performed on water confined in silica substrates. Similarities and differences between the two cases clearly show up, as far as both microscopic structure and single proton dynamics are concerned. In particular in both supercooled bulk water and water under confinement we observe a closer average distance between first neighboring oxygen sites and shortening of the H-bonds. In contrast the number of H-bonds per molecule and the number of interstitial water molecules are severely reduced under confinement, and the second peak of the oxygenoxygen radial distribution function is shifted to shorter distances, compared to the bulk phase. Based on these results a possible scenario for understanding changes evidenced by deep inelastic neutron scattering when water is either confined or supercooled is proposed.