Particle-size dependent stability of co-continuous polymer blends

The properties of polymer blend nanocomposites are typically associated with spatiotemporal distribution of nanoparticles within a polymer blend system. Here, we present in situ high-temperature confocal rheology studies to assess the effect of particle size on the extent of particle agglomeration, particle migration, and subsequently their influence on the coarsening dynamics of polymer blends filled with pristine silica particles. We investigate co-continuous polypropylene-poly(ethylene-co-vinyl acetate) blends filled with five different silica particles with a diameter ranging from 5 to 490 nm. While particle size does not play a role when particles are thermodynamically driven to their preferred polymer phase, a striking effect is achieved when particles are kinetically trapped at the interface. We find that the interparticle interaction largely driven by size dependent long-range repulsive forces governs their extent of agglomeration, severely affecting their ability to stabilize co-continuous morphology. Strikingly, the largest (490 nm) particles are more effective in suppressing coarsening than 5 nm particles, while 140 and 250 nm particles are found to be the most effective. We demonstrate that kinetic trapping of primary particles of either size is influenced by the interplay of interfacial folding during melt blending and Laplacian pressure exerted at the interface. These results extend our fundamental understanding of the stabilization of co-continuous morphology in polymer blends by particles.