Dynamic Heterogeneities of Rod Rotation in Macromolecular Networks

Understanding the rotational diffusion dynamics and underlying physical mechanism of rod-like particles in the confinement environments of macromolecular networks is of great importance in many fields. Herein, by combining large-scale simulations as well as theoretical analysis, we demonstrate that the thick rods, with rod diameter comparable with or even larger than the mesh size, in macromolecular networks possess enhanced heterogeneous rotational diffusion characterized by evident hopping among various preferred angles. Through quantifying the shape-dependent rotation, three characteristic rotational dynamics, i.e., Brownian, hopping, and restricted, are identified, which leads to a phase diagram of these rotational patterns related to the diameter and length of the rods. We find that the strong dynamic correlation between the hopping of the rotational and translational dynamics occurs at the boundary between the hopping and restricted rotational dynamics, beyond which the transitional dynamics presents diverse dynamic patterns during the rotational hopping. Furthermore, we develop an analytical model that captures all the regimes of the characteristic rotational patterns, resulting in a mechanistic interpretation of the emergence of the hopping rotational dynamics. The findings bear significance in unraveling the fundamental physics of anisotropic particles transporting in confined mediates like macromolecular networks.