Dynamics of Semidilute Polymer Rods: An Alternative to Cages

Brownian simulations of rods with variable diameter $d$ show that the rotational friction constant ${\beta }_{\mathrm{rot}}$ is the same in the limit $d\to 0$ as for a probe rod in a system in which vicinal rods interact with the probe but not with each other. This agreement seems to rule out cage models. A model based on the rapid dissipation of cage forces accounts for the observed dependence of ${\beta }_{\mathrm{rot}}$ on concentration $c$, length $L$, and $d$.