FLUORESCENCE AND LIGHT-SCATTERING-STUDIES OF SOL-GEL REACTIONS

A fluorescence probe sensitive to local viscosity and local free volum e has been used to study the curing behavior of several gel systems us ed to make aerogels. For the same systems, complementary information r egarding the molecular structure (molecular weight, molecular radius, and second virial coefficient) of the sols and solutions has been dete rmined from static light-scattering measurements. These studies reveal clear differences in both the curing behavior and molecular structure of ''polymeric'' and ''colloidal'' systems and show the importance of thermodynamic solvent quality, a parameter traditionally ignored in s ol-gel processing.