INFLUENCE OF THE MICROSTRUCTURE ON THE MACROSCOPIC ELASTIC AND OPTICAL-PROPERTIES OF DRIED SONOGELS - A BRILLOUIN SPECTROSCOPIC STUDY

The elastic and optical properties of organically modified silicates p repared by ultrasonics aided polycondensation of tetraethoxysilane and polidimethylsiloxane are studied by means of high resolution Brilloui n spectroscopy, Nuclear magnetic resonance data evidence the microsepa ration of the organic and inorganic phases for the systems with high c ontent of polymer formation. The elastic and optical properties are cl early influenced by the change in microstructure, We propose a three c omponent mechanical model that qualitatively explains the observed var iation of the elastic constant c(11) versus molar fraction of dimethyl siloxane in these vitreous materials and develop a structural model th at accounts for the observed dynamical behavior. (C) 1997 American Ins titute of Physics.