Modifications of the hydrogen bond network of liquid water in a cylindrical SiO2 pore

We present results of molecular dynamics simulations of water confined in a silica pore. A cylindrical cavity is created inside a vitreous silica cell with geometry and size similar to the pores of real Vycor glass. The simul ations are performed at different hydration levels. At all hydration levers water adsorbs strongly on the Vycor surface; a double layer structure is e vident at higher hydrations. At almost full hydration the modifications of the confinement-induced site-site pair distribution functions are in qualit ative agreement with neutron diffraction experiment. A decrease in the numb er of hydrogen bonds between water molecules is observed along the pore rad ius, due to the tendency of the molecules close to the substrate to form hy drogen-bonds with the hydrophilic pore surface. As a consequence we observe a substrate induced distortion of the H-bond tetrahedral network of water molecules in the regions close to the surface. (C) 2000 Elsevier Science B. V. All rights reserved.