Acoustic resonance in tetramethoxysilane matrices: A new tool to characterize the gel formation

Several techniques have been used to approach the sol-gel transition. This article develops a new technique based on the evolution of a transmitted ac oustic wave through the tetramethoxysilane (TMOS) bulk. The applied frequen cies lie within the lowest part of the audible range. The sol-gel transitio n is assessed by the evolution of resonance peaks. The temporal evolution o f the associated resonance frequencies is depicted through a number of curv es, each one representing a harmonic mode. Moreover, the shape of these cur ves is very similar to that obtained in alcogels for the evolution of the c omplex shear modulus. They converge towards a unique intersection point wit h the time axis, which corresponds to the gelation time. An appropriate num erical treatment shows that the building process of the network in gel phas e is not influenced by the silicon initial concentration and hydrolysis mol ar ratio range. However, above a certain silicon initial concentration, dep artures from the unique curve take place. These departures are assumed to b e due to aggregations between precursor molecules. (C) 2001 American Instit ute of Physics.