Nanoparticle dynamics in semidilute polymer solutions: rings versus linear chains

Understanding the dynamics of nanoparticles in polymer solutions is important for applications in drug delivery and enhanced oil recovery. The dynamics of nanoparticles deviate from the generalized Stokes-Einstein relation when the size of nanoparticles and polymers are comparable as the polymer solution cannot be treated as a homogeneous medium. Dynamics of nanoparticles in semidilute solutions of ring and linear polymers are studied using coarse-grained hybrid molecular dynamics–multiparticle collision dynamics simulations to capture hydrodynamic interactions. The long-time diffusion coefficients of the nanoparticles follow the predictions of a polymer coupling theory by Cai et al., Macromolecules 44, 7853–7863 (2011). At intermediate time scales, the subdiffusive exponents of nanoparticles are strongly correlated to those of the polymer center-of-mass for both rings and linear chains and deviate from coupling theory. Hence, the nanoparticle dynamics are strongly coupled to the polymer center-of-mass motions for both architectures rather than to their segmental dynamics. The presence of ring concatenations slightly reduces the subdiffusive exponents of the nanoparticles and the polymer center of mass, but the long-time diffusivity of the nanoparticles remains almost constant.