Diffusion of Sticky Nanoparticles in Unentangled Polymer Melts

Large-scale molecular dynamics simulations are used to study the diffusion of sticky nanoparticles in unentangled polymer melts, which models the transport of nano-scale objects in a sticky and viscous environment such as the polymer matrix in a polymer nanocomposite and complex fluids in a respiratory droplet. The simulated particles are larger than the average size of the polymers, and their diffusion coefficients follow the Stokes-Einstein relation.  In the athermal limit, the hydrodynamic radius r_H equals the bare particle radius r, and the particle-polymer boundary condition depends on polymer slippage over the particle surface. With increasing attractive interaction between the nanoparticles and the matrix (stickiness),  r_H remains equal to r, while polymer slippage is gradually suppressed. As the stickiness further increases, r_H is enlarged compared to r, with the particle-polymer boundary condition being no-slip. r_H increases because the nanoparticle moves together with longer sections of the adsorbed polymers. Eventually for sufficiently strong stickiness, r_H saturates at a value controlled by the sum of  r and the thickness of the entire adsorbed polymers. Sticky nanoparticles with r_H > r can be mapped to polymer-tethered nanoparticles.