Nanotetrapods promote polymer flow through confinement induced packing frustration.

Processing ultra-high molecular weight polymers presents significant experimental challenges due to their high viscosity, which requires elevated shear rates and consequently increases energy demands. Here, we explore the role of the geometry of nanoparticles- spheres, rods, and tetrapods - in controlling the effective viscosity of polymer nanocomposites. Intriguingly, our combined experiments and molecular dynamics simulations reveal a significant decrease in the viscosity of composites with tetrapod nanoparticles, without compromising mechanical or thermal integrity, unlike sphere and rod, which exhibit minimal impact on the viscosity at the same level of loading. We show that the inner curvatures of the nanotetrapods impose strong physical confinement introducing an entropic cost for polymers to access this space. The inaccessible volume creates polymer packing frustration around nanotetrapod surfaces, which, in turn, increases their mobility and decreases the overall viscosity of the composite. Nanotetrapods prove to be effective flow promoters while preserving good dispersion within a polymer melt, offering significant potential for advanced polymer processing applications.