Unexpected crossover dynamics of single polymer in a corrugated tube

We present molecular dynamics study of a generic (coarse-grained) model for single-polymer diffusion confined in a corrugated cylinder. For a narrow tube, i.e., diameter of the cylinder $\delta <2.3$, the axial diffusion coefficient $D_{\mathrm{\mid }\mathrm{\mid }}$ scales as $D_{\mathrm{\mid }\mathrm{\mid }}\propto N^{-3\mathrm{/}2}$, with chain length $N$, up to $N \approx 100$thencrossesovertoRousescalingforthelarger$N$values\mathrm{.}The$N^{-3/2}$ scaling is due to the large fluctuation of the polymer chain along its fully stretched equilibrium conformation. The stronger scaling, namely $N^{-3\mathrm{/}2}$, is not observed for an atomistically smooth tube and/or for a cylinder with larger diameter.