Nanoparticle dynamics in semiflexible ring polymer solutions

Understanding the transport of nanoparticles (NPs) in polymer solutions is important for applications such as targeted drug delivery and enhanced oil recovery. When the size of NP and polymers are comparable, the polymer solution cannot be treated as a continuum fluid and the NP dynamics deviate from the prediction of the generalized Stokes-Einstein relation. We studied the effects of polymer backbone stiffness on the dynamics of NP in semi-dilute ring polymer solutions using hybrid molecular dynamics–multiparticle collision dynamics simulations. The long-time diffusion coefficients of NPs decrease with an increase in the stiffness of ring polymers and deviate from the predictions of a polymer coupling theory by Cai et al. [Macromolecules 44, 7853–7863 (2011)]. At intermediate time scales, the NP subdiffusive exponents in fully flexible ring polymer solutions are strongly correlated to those of the polymer center-of-mass (COM), suggesting NPs dynamics are coupled with dynamics of polymer COM. Upon increasing backbone stiffness, however, we observe that the NP and polymer COM dynamics begin to decouple. We discuss these observations in the context of expectations from polymer coupling theory and contrast with those from complementary studies of NP dynamics in solutions of linear polymer chains.