EPR spectroscopic investigation of the sol–gel transition in modified tetraethylorthosilicate gels

Abstract

Cu 2+ ions are used to follow the sol–gel transition in amino-modified TEOS mixtures. In contrast to unmodified TEOS gels, fixation of the spin probe (Cu 2+) to the sol particle surface takes place and changes in mobility are detectable. Furthermore, we find changes in the coordination sphere of the copper ions and a temporary loss of EPR intensity. By using a simple kinetic model it is possible to estimate the rate constants of the condensation and syneresis processes.