Adsorption of water on porous Vycor glass studied by ellipsometry

The variation of the optical properties of porous Vycor glass (Corning, Model 7930) under different relative-humidity conditions was studied. The adsorption of water into the glass pores was investigated with spectroscopic ellipsometry. The change of the refractive index was Deltan similar to 0.04 between 5% and 90% relative humidity. A Linear relation between the ellipsometer parameter tan Psi, the amount of water adsorbed in the glass pores, and information about the pore-size distributions was established. The results are in accord with the values obtained from N-2 isotherms, transmission electron microscope micrographs, and the manufacturer's specifications (radius of similar to 20 Angstrom). The possibility of using this material as a transducer for implementation in a fiber-optic sensor to measure humidity was evaluated. (C) 2001 Optical Society of America.