APPEARING, DISAPPEARING, AND REAPPEARING FUMED SILICA NANOPARTICLES: TAPPING MODE AFM EVIDENCE IN A CONDENSATION CURED POLYDIMETHYLSILOXANE HYBRID ELASTOMER

In the present research, a technology was used to prepare amorphous fumed silica nanoparticles (FSN) PDMS hybrids. In surface analysis by tapping-mode atomic force microscopy (TM-AFM) of the hybrid materials, we found that for certain compositions and cure conditions the near surface FSN seem to “disappear”. The inability to image near-surface nanoparticles was explained by the formation of an amorphous reticular siliceous surface domain that mechanically isolated near surface nanoparticles. This result showed that nanoparticles can act as “reporters” for secondary siliceous domain structure buildup. Herein, we report surprising new developments for FSN PDMS hybrid nanocomposite materials. Nanoparticles “reappear” or “never appear” depending on composition and nanoparticle surface chemistry. On the basis of information from the reporter nanoparticles, we propose a model for siliceous phase secondary structure buildup that incorporates the TM-AFM results.