Structure and Dynamics of a Polymer–Nanoparticle Composite: Effect of Nanoparticle Size and Volume Fraction

We use molecular dynamics simulations to study a semidilute, unentangled polymer solution containing well-dispersed, weakly attractive nanoparticles (NP) of size (σN) smaller than the polymer radius of gyration Rg. We find that if σN is larger than the monomer size the polymers swell, while smaller NPs cause chain contraction. The diffusion coefficient of polymer chains (Dp) and NPs (DN) decreases if the volume fraction ϕN is increased. The decrease of Dp can be well described in terms of a dynamic confinement parameter, while DN shows a more complex dependence on σN, which results from an interplay between energetic and entropic effects. When ϕN exceeds a σN-dependent value, the NPs are no longer well dispersed and DN and Dp increase if ϕN is increased.