Manipulating the Properties of Polymer Nanocomposites via Ring-Grafted Nanoparticles

Enhancing polymer performance through nanocomposite strategies has emerged as an effective approach to achieve superior mechanical strength. We systematically investigated the mechanical reinforcement mechanisms of polymer composites containing ring-grafted chain nanoparticles (RGCPs) using molecular dynamics simulations. The effects of the grafted-chain assembly fraction φasse, polymer matrix chain stiffness k, and interfacial interaction strength εnp on stress transfer, entanglement formation, and overall mechanical performance were examined. Moderately short ring-grafted chains (φasse = 0.25) form a dense network of entanglements, resulting in the highest yield strength and optimal stress transfer at low to moderate strains. At high strains, however, extensive disentanglement of these entanglements causes the stress to fall below that of the φasse = 0.50 system. A matrix chain stiffness of k = 60ε/σ2 ensures sufficient chain penetrability while maintaining stable entangled structures, yielding the optimal mechanical performance. Interfacial interactions exhibit strain-dependent effects: a moderate increase in εnp promotes effective contact between grafted chains and polymers, enhancing entanglement and mechanical properties, whereas excessively strong attractive interactions cause the matrix chains to aggregate on the surfaces of the grafted rings, thereby suppressing their penetration and entanglement. Comparison with linear-grafted (LGCPs) and free-ring (RCPs) systems reveals that, relative to linear polymers with free ends, the closed-loop topology of ring-grafted chains uniquely facilitates entangled structures and improves material strength and toughness, although these entanglements are more prone to disentanglement under cyclic tensile loading. Furthermore, clustered nanoparticles reduce the mobility of ring-grafted chains, limiting their entanglement with the matrix chains. This work provides a microscopic understanding of the complex interplay among polymer conformation, entanglements, and chain dynamics in mechanical reinforcement, offering theoretical guidance for the design of high-strength and durable polymer composites.