A composition-morphology mapping of fumed silica filled polymer blends

We explore the effects of adding fumed silica particles to blends of two immiscible homopolymers, polyisobutylene (PIB) and polyethylene oxide (PEO) across a wide range of composition. Blends of PIB and PEO with fumed silica loading up to 10 vol% were studied. The fumed silica has strong affinity for PEO, and hence, when there is enough PEO to fully engulf the particles, a combined phase of fumed silica-in-PEO is formed. Due to the fractal-like nature of fumed silica particles, this combined phase can be strongly solid-like even at low particle loadings. We observed two morphological changes different from what was observed in spherical particulate filled in polymer blends studied in the past. The first is that, at low loadings of fumed silica, a huge qualitative change was seen in the morphology of the polymer blends. More specifically, particle-free blends that showed a dispersed phase microstructure often became cocontinuous upon adding particles. The second is when fumed silica together with the PEO formed a combined phase, a capillary aggregates network survived across a wide range of composition at 10vol% fumed silica loading.