Decoupling the interplay of polymer properties and particle size in stability of co-continuous blend composites

Interfacially localizing particles in co-continuous polymer blends requires a complex interplay between the properties of polymers, such as interfacial tension between them, $Γ$⁠, viscosity, η, viscosity ratio between them, and particle properties, such as particle size and particle surface chemistry. Here, we investigate the formation and coarsening dynamics of four co-continuous blend composites based on polypropylene, PP (or linear low-density polyethylene), and poly(ethylene-co-vinyl acetate), EVA filled with pristine silica of two sizes (140 and 250 nm). By choosing polymer blend components with different viscosities and interfacial tensions and particles with varying size and size distributions, we were able to elucidate their relative contributions in the stabilization of co-continuous polymer microstructures. By utilizing confocal rheology, we show that the evolution of storage modulus during coarsening of polymer blend composites is primarily dependent on the strength of the initial interfacial particle network. Our findings indicate that the initial domain size and kinetic control of interfacial particle localization in co-continuous polymer blends are determined by the $Γ$/η ratio of the neat blend. However, this relationship does not hold in low viscosity systems. When polymer blend viscosity is lower, it reduces the kinetic barrier at the interface, leading to a higher proportion of particles localizing in the favorable EVA phase. We also find that the smaller particles have a higher propensity for interfacial localization. These findings provide insight into the success of kinetic particle trapping at the interface of co-continuous blends and the resulting composite properties based on the choice of component properties.