The drag of the tails: Diffusion of sticky nanoparticles in dilute polymer solutions

We devise a simple coarse-grained model of a nanoparticle exhibiting attractive interactions with a polymer in good solvent and use Monte Carlo simulations to study how adsorption of the polymer affects the hydrodynamic properties of the nanoparticle. We show that the hydrodynamic radius of the polymer-decorated nanoparticle increases with increasing polymer chain length or concentration. The slowdown of diffusion of the sticky nanoparticles is predicted to occur at polymer concentrations many orders of magnitude below the overlap concentration, in contrast with the case of non-sticky nanoparticles. To rationalize our findings, we employ the concept of trains, loops, and tails, which has been used in earlier theoretical studies of polymer adsorption at interfaces. We show that dominant contribution to the increase of the hydrodynamic radius of the polymer-decorated nanoparticles comes from the tails, which stretch far from the surface. On the contrary, the much more numerous but shorter loops and tails play only a minor role.