In Situ Silica Nanoparticle Formation in a Rubber Matrix Monitored via Real-Time SAXS and Solid-State NMR Spectroscopy

Abstract

Silica formation in a rubber matrix is studied. The hypothesis that the formation proceeds via inverse micelles where the hexylamine present, being a catalyst, also behaves as a surfactant, is made highly plausible. As well-known, the conversion of TEOS into a solid silica particles proceeds via hydrolysis and condensation reactions. These transformations of TEOS comprise consequential substitution of the hydroxyl (−OH) groups with siloxane ones (−OSi), labeled as Q1: one −OSi group; Q2: two −OSi groups; Q3: three −OSi groups; and Q4: four −OSi groups. Here the kinetics of the sol–gel reaction in the rubber matrix was studied as a function of the reaction temperature (40–120 °C) by 1H high-resolution magic-angle spinning (HR-MAS) NMR spectroscopy. Real-time small-angle X-ray scattering (SAXS) measurements of the sol–gel reaction in NR and EPDM rubber matrices were performed in a time scale of 1 s to 60 min with images being acquired every 15 s. The sol–gel reaction in NR and EPDM rubber at 100 °C shows an...