Translational and rotational dynamics of an ultra-thin nanorod probe particle in linear polymer melts.

The dynamics of nanorods (NRs) in complex liquids is important, not only for new material design and for understanding complex phenomena in biological systems, but also for the development of fundamental theories. In this work, the translational and rotational dynamics of a single rigid ultra-thin nanorod probe particle in linear polymer melts are investigated using coarse-grained molecular dynamics (CG-MD) simulations. Our results indicate that the translational motion of an ultra-thin NR, which has a diameter equal to the polymer monomer size, is not affected by the polymer chain length N in entangled polymer melts. This finding verifies de Gennes' theoretical prediction for the first time. However, the rotational dynamics of a NR with rod length L = 21, which is larger than the polymer tube diameter dt, is weakly coupled with polymer entanglement strands, revealing a different N-dependence for translational and rotational dynamics. The results for NRs with different lengths L also show that the size ratio between L and the polymer characteristic size is the dominant factor for NR dynamics, especially for rotational dynamics in entangled melts.