Structural and physical properties of Ag doped poly(dimethylsiloxane) modified silica xerogels

The purpose of the present work is to study the effect of silver (Ag) incor poration on the structural and physical properties of poly(dimethylsiloxane ) (PDMS) modified silica xerogels. PDMS was chosen as the organic component because of its similarity of backbone structure (-Si-O-) with tetraethyl o rthosilicate, the inorganic component of organically modified silicates. In the present work silver was incorporated by two routes: (i) directly in th e sol and (ii) silver doping was done after preformed porous matrix was obt ained. The microstructures, particle size distribution, infrared spectra, a nd optical coloration have been studied. The utility of two methods has bee n discussed. It was found that the particle size was much smaller compared with that of classical gels with dispersed Ag particles. For the indirect m ethod of silver doping the particle size distribution was found to follow l og-normal distribution function. Upon exposure to humid air the samples cha nge optical state from transparency to opacity. However, this was found to be reversible when treated above 300 degreesC. This phenomenon may be utili zed to fabricate humidity sensor and optical switches. (C) 2001 American In stitute of Physics.