BRILLOUIN SPECTROSCOPY ON DRIED SONOGELS

The elastic properties of organically modified silicates prepared by u ltrasonics aided polycondensation of Tetraethoxysilane and Polidimethy lsiloxane is studied by means of high resolution Brillouin spectroscop y. Our results evidence the microseparation of the organic and inorgan ic phases for the systems with high content of polymer. We propose a m echanical model that qualitatively explains the observed variation of the elastic constant c(11) vs molar fraction of dimethylsiloxane in th ese vitreous materials and develop a structural model that accounts fo r the observed dynamical behavior. (C) 1996 American Institute of Phys ics.