Silane coupling agent and dispersion in silica nanocomposites

Dispersion of nano-silica in polybutadiene and SBR is of interest to the elastomer industry. Often, silane coupling agents are used for compatibilization. This is done by melt blending untreated precipitated silica, a coupling agent, and elastomer in a Brabender mixer. The coupling agent contains sulfur that can react with vinyl groups in the elastomers as well as ethoxy groups that can react with surface hydroxyl groups on silica. We have quantified the extent of these two reactions using IR spectroscopy, and quantified the dispersion using microscopy and small-angle x-ray scattering (SAXS). From SAXS we obtain the second virial coefficient which is used as a measure of dispersion.