Direct Evidence of the Liquid−Solid Transition of a Sol−Gel Material Using Photoacoustic Spectroscopy

The gelation process of a sol−gel material is monitored for the first time in a detailed manner by use of a photoacoustic spectroscopy derived methodology. Measurements of the acoustic response spectrum of a sol−gel material during the transition permits a clear monitoring of the sol−gel evolution as well before macroscopic gelation as afterward. Different phases are inferred corresponding to the three first proceeding steps of the material formation.