Sol-gel particle growth studied using fluorescence anisotropy: An alternative to scattering techniques

The aggregation of silica particles during hydrogel polymerization has been observed in sitar with angstrom resolution using the combined fluorescence anisotropy decay of solvated and bound dye. Primary particles of mean hydrodynamic radius approximate to 1.5 nm are found to be present within 20 min of mixing sodium silicate solution and sulfuric acid. Clustering then occurs during siloxane polymerization to produce after approximate to 30 h secondary particles with a mean radius up to approximate to 4.5 nm at a growth rate that depends on silicate concentration and time to microgelation t(g). Subsequent condensation to approximate to 4 nm radius occurs within 1 week as particle syneresis dominates.