Diffusion of Thin Nanorods in Polymer Melts

The diffusion of monomerically thin nanorods in polymer melts is studied by molecular dynamics simulations. We focus on the systems where the chains are long enough to screen the hydrodynamic interactions, in which case the diffusion coefficient D-parallel to for the direction parallel to the rod decreases linearly with increasing rod length l. In unentangled polymers, the diffusion coefficient for the direction normal to the rod exhibits a crossover from D-perpendicular to similar to l(-2) to similar to l(-1) with increasing l, corresponding to a progressive coupling of nanorod motion to the polymers. Accordingly, the rotational diffusion coefficient D-R approximate to D(perpendicular to)l(-2)similar to l(-4) and then D-R similar to l(-3) as l increases. In entangled polymers, D-perpendicular to and D-R are suppressed for l larger than the entanglement mesh size a. D-perpendicular to similar to l(-3) and D-R similar to l(-5) for l-sufficiently above a, in agreement with de Gennes' rod reptation model.

Automated summary

The diffusion of monomerically thin nanorods in polymer melts is affected by both chain length and entanglement, leading to varying diffusion coefficients in different directions with increasing rod length. The findings show a complex relationship between nanorod motion and polymer properties.