Diffusion of Nanosheets in Unentangled Polymer Melts

Understanding the dynamics of nanosheets in polymer matrices is crucial for the processing of polymer nanocomposites and their applications in drug delivery. In this work, we investigate the diffusion of thin nanosheets in unentangled polymer melts using molecular dynamics simulations. We show that for nanosheets smaller than a characteristic size l_c, which is a few times the polymer chain size, the continuum hydrodynamic theory based on macroscopic viscosity breaks down and significantly underestimates the diffusion coefficients. For nanosheets with sizes l < l_c, we derive scaling relationships for both translational and rotational diffusion coefficients as functions of l and further reveal the dynamical coupling between nanosheet motion and the modes of the polymer melt. For l > l_c, the continuum theory is recovered. Our findings reconcile the continuum and scaling theories for the diffusion of nanoparticles in polymer melts.