Capillary-driven percolating networks in ternary blends of immiscible polymers and silica particles

We investigate the structure and rheology of a melt-blended ternary system composed of a continuous polymer phase, silica particles in the few-micron size range, and a small amount of a second immiscible polymer phase which preferentially wets the particles. The morphology of the ternary system is found to consist of a volume-spanning pendular network of particles bridged by menisci of the wetting polymer, as well as capillary aggregates which are large compact particle aggregates saturated by the wetting polymer. The ternary blends have strongly non-Newtonian melt rheology due to the pendular network. The relative extent of capillary aggregation depends on the melt-blending history, and the rheological properties can be used to track the changes in the blend structure. The pendular network is seen at a particle loading of only 10 vol.%, demonstrating that capillary bridging lowers the percolation threshold of a particle-filled polymer.