Silver doped ORMOSIL - an investigation on structural and physical properties

Doping of classical silicate glass prepared by sol-gel technique by Ag or other manometer size metal particles have made a major stride in past decade. But studies of metallic particle incorporated organically modified silicates (ORMOSIL) are quite scarce. The present work attempts to study the effects of Ag doping on the structural and physical properties of poly(dimethylsiloxane) (PDMS) modified silica xerogels. The choice of tetraethoxysilane (TEOS) and PDMS its the starting inorganic and organic components. respectively. for the preparation of ORMOSIL was dictated by the similarity in their backbone structure (-Si-O-). Ag nano particles were incorporated by two routes: (i) directly into the sot by adding calculated amount of AgNO3 prior to gelation. and (ii) in this case preformed porous matrix was obtained first and then Ag doping was done by immersion of that matrix in AgNO3 solution for several days and subsequent heat treatment. Microstructures (SEM, TEM, XRD), particle size distribution, infrared response (FTIR) and density have been studied. It was found that the Ag particles in the sample prepared by the second route were less prone to aggregation compared with that prepared using First route. The merits and demerits of the two methods have been discussed. It was observed that when exposed to humid air, the samples changed the optical state from transparency to opacity to various degrees depending on the amount of Ag incorporation. However, transparency could be brought back by treating the sample at a temperature above 300 degreesC. This phenomenon exhibits its potential to be used as humidity sensor and/or optical switches. (C) 2002 Elsevier Science B.V. All rights reserved.