Substituent-dominated structure evolution during sol-gel synthesis: a comparative study of sol-gel processing of...

The sol-gel processes of 3-glycidoxypropyltrimethoxysilane (GPTMS) and methacryloxypropyltrimethoxysilane (MAPTMS) have been followed by fluorescence spectroscopy with pyranine as a photophysical probe. The experimental results showed that this probe is sensitive to the structural evolution and microenvironment polarity. The specific comparison of the structural evolution in two substituted organotrialkoxysilanes, namely, MAPTMS and GPTMS, illustrates the ability of the substituents to interact with the microenvironment via electrostatic interactions. Interestingly, these interactions determine the kinds of intermediate supramolecular structures that form during the sol-gel process and hence control the structure of the ensuing sol-gel end product. In particular, the amphiphile-like character of the MAPTMS intermediates contrasts with the biamphiphilic character of their GPTMS counterparts, driving distinctly different transient and local molecular organizations, which in turn modulate the hydrolysis and condensation reactions during the sol-gel process.