  Transport of rodlike particles in confinement environments of macromolecular
networks plays crucial roles in many important biological processes and
technological applications. The relevant understanding has been limited to thin
rods with diameter much smaller than network mesh size, although the opposite
case, of which the dynamical behaviors and underlying physical mechanisms
remain unclear, is ubiquitous. Here, we solve this issue by combining
experiments, simulations and theory. We find a nonmonotonic dependence of
translational diffusion on rod length, characterized by length
commensuration-governed unconventionally fast dynamics which is in striking
contrast to the monotonic dependence for thin rods. Our results clarify that
such a fast diffusion of thick rods with length of integral multiple of mesh
size follows sliding dynamics and demonstrate it to be "anomalous yet
Brownian". Moreover, good agreement between theoretical analysis and
simulations corroborates that the sliding dynamics is an intermediate regime
between hopping and Brownian dynamics, and provides a mechanistic
interpretation based on the rod-length dependent entropic free energy barrier.
The findings yield a principle, that is, length commensuration, for optimal
design of rodlike particles with highly efficient transport in confined
environments of macromolecular networks, and might enrich the physics of the
diffusion dynamics in heterogeneous media.
