Anomalous Molecular Weight Dependence Reveals the Origin of Mechanical Enhancement in Polymer Nanocomposite

Abstract: Polymers at the interface exhibit frustrated chain conformation distinct from the bulk, impacting particle dispersion and properties of polymer nanocomposites (PNCs). Utilizing bimodal molecular weight (MW) PNCs, we observed unusual chain elongation of interfacial polymers, which promotes networked structures at low particle loadings. Paradoxically, reducing the average MW in bimodal PNCs significantly enhances the shear modulus by up to 103 times, challenging the conventional preference for higher MW in property enhancement. The mechanical reinforcement, aided by stretched chains, manifests when the short chain is substantially shorter than the long chain (Rg ratio >~2), indicating a universal stretching factor of 2.3.