Strain hardening from deformation-induced nanoparticle-nanoparticle interaction of polymer nanocomposites

Understanding the structure-property relationship of polymer nanocomposites (PNCs) during deformation is crucial for PNC processing. In this work, we investigate the roles of external deformation on the nanoparticle-nanoparticle interactions through a combination of small-angle x-ray scattering and rheology. We found the applied uniaxial extension brought together the NPs at the transverse stretching and catalyzes the percolation transition of nanoparticles. The percolated nanoparticle network thus leads to a strong surge in the elongation viscosity at yielding, leading to an unexpected strain hardening at large deformation. Interestingly, the yield strain, ε_Y, and yield stress, σ_Y, of the percolated nanoparticle network follow a scaling of ε_Y ~ (dε/dt)⁰, and σ_Y ~ (dε/dt)^0.5 regardless of the loading of NPs, where the dε/dt is the Hencky strain rate. These observations manifest the unconventional roles of external deformation on modulating the nanoparticle-nanoparticle interaction, enabling advanced structures and properties control of PNCs.