Water on silica and silicate surfaces. III. Hexamethyldisilazane-treated silica surfaces

Abstract

Both a fully hydroxylated (HiSil) and a partially hydroxylated silica (Cab-O-Sil) were titrated to increasing coverage by HMDS. The hydrophobicity induced by the chemisorption of the (CH 3) 3 Si-groups was then monitored by water vapor adsorption isotherms as a function of ligand coverage. The Cab-O-Sil was made strongly hydrophobic whereas the underlying, unreacted OH's on the HiSil, even at full coverage of one ligand per 40 A 2, remained available to the water molecules. Reflectance ir was employed to examine the HMDS and the water interaction with the modified silica surfaces; a new major revelation was the N—H band indicating conclusively that ammonia from the disilazane was also adsorbed.