Simulating Nanoparticle Dynamics in Semidilute Polymer Solutions

The dynamics of polymers and particles in nanocomposites are of great interest in materials processing. Particle mobility is well described by the generalized Stokes-Einstein relation when the particles are much larger than the polymers, but less understood when it comes to smaller or comparable sized particles. We investigate this smaller sized regime using advanced particle-based simulation techniques, with the multi-particle collision dynamics (MPCD) scheme modeling solvent-mediated hydrodynamic interactions. We demonstrate that the translational center-of-mass motions of both particles and polymers are sub-diffusive on short times before transitioning into the diffusive regime, and the highly correlated sub-diffusive exponents suggest that not only local polymer relaxations but also polymer center-of-mass motions play a role in the coupling between the dynamics of polymers and nanoparticles. Finally, we perform simulations tuning flexibility of the polymers, and as the persistence length increases, the particle dynamics become more sub-diffusive and decouple from the dynamics of the polymer chain center-of-mass.