Neutron diffraction study of the pore surface layer of Vycor glass

Analysis of small-angle scattering and powder diffraction data combined with macroscopic measurements have revealed the structure of a pore surface layer in Vycor glass, consisting of OH groups and chemisorbed water. Chemisorbed water exists on the pore surface in two forms: compact water clusters of {~}40--60 molecules, connected to each other by hydrogen bonds, and more spaciously distributed individual molecules (or groups of several molecules). Heating to 650 ^∘{}C reconstructs the pore surface: the number of OH groups is significantly decreasing due to the reaction of dehydration between Si-OH and B-OH surface groups. However, the temperature treatment does not affect the process of H₂O clusters formation, which still appear on the pore surface after the condensation.