Thermogravimetric Analysis of the Kinetics of the Reaction of Alkoxysilane with Silica

The surface functionalization of silica by alkoxysilane can improve its dispersion into polymers by beneficially modifying interparticle and particle-polymer interactions.  Thermogravimetric analysis (TGA) has been used to study the kinetics of binding a bi-functional alkoxysilane onto silica over the temperature range of 50 to 110°C. Derivative TGA curves of the reacted silica show distinct peaks which correspond to the alkoxysilane bound to one or two surface silanol sites.  Binding at two silanol sites is postulated to occur in a two-step series reaction model.  An Arrhenius analysis for the alkoxysilane binding reactions shows that the activation energies of the two reaction steps are similar, which is expected since the alkoxysilane contains two identical binding groups.  This work demonstrates the suitability of the TGA technique to investigate the reaction kinetics for modifying the surface of silica.