Water adsorption on silica and calcium-boroaluminosilicate glass surfaces—Thickness and hydrogen bonding of water layer

Adsorption isotherm of water on silica (modeled with fused quartz) and calcium-boroaluminosilicate (Ca-BAS) glass surfaces as a function of relative humidity (RH) was studied using Fourier transform infrared (FTIR) spectroscopy. The effective thickness of the adsorbed water layer and the distribution of hydrogen bonding interactions of water molecules in the adsorbed layer were determined by comparing the transmission FTIR spectra collected at the Brewster incidence angle with the theoretically calculated spectra. In the sub-monolayer regime (<30% RH), differences between the water spectra on fused quartz and Ca-BAS glass could be related to the areal density of hydroxyl groups as well as the elemental composition of the surface determined with x-ray photoelectron spectroscopy. In the transition regime (30%–60% RH), multilayers start growing and the difference between the fused quartz and Ca-BAS surfaces diminishes as the humidity increases. In the multilayer regime (>60% RH), the total amount as well as the hydrogen bonding interactions of adsorbed water layers become insensitive to the surface chemistry and are governed mostly by the phase transition (vapor condensation) behavior. Overall, this study reveals how the water layer thickness and structure on the multicomponent silicate glass surface in ambient conditions are different from those on the pure silica surface.