Influence of Nanoparticles on the Structure, Dynamics, and Mechanical Behavior of Nonconcatenated Ring Polymers

The structure and dynamics of polymers in the presence of nanoparticles (NPs) determine the macroscopic properties of polymer-nanoparticle composites (PNCs). Through molecular dynamics simulations, we investigate the effects of spherical NPs on the conformation, segregation, topological constraints (TCs), dynamics, and mechanical behavior of nonconcatenated ring polymers, varying the NP volume fraction phi from 0 to 44%. Depending on phi, the geometrical constraints induced by the NPs have distinctly different effects on the dimension, anisotropy, and segregation of the ring polymers. At low phi, ring polymers exhibit more compact conformations and enhanced segregation compared to ring polymers in neat melts, whereas at high phi, ring polymers become more anisotropic with increasing phi. Unexpectedly, the TCs between ring polymers in the PNCs deviate slightly from those in neat ring polymers. In contrast, the TCs induced by neighboring ring polymers and NPs increase significantly with increasing phi. At a critical NP volume fraction phi(c) approximate to 0.3, the constraints restricting the dynamics of ring polymers transition from inter-ring TCs to "NP entanglements". Simulation results of uniaxial stretching and stress relaxation demonstrate the profound effect of TCs on the mechanical response of the PNCs. Our findings provide a microscopic understanding of the static and dynamic properties of ring polymers in the PNCs and offer valuable insights into tuning the properties of ring PNCs by adding NPs.