  We performed molecular dynamics simulations with a coarse-grained model to
investigate the capillary filling dynamics of polymer chains in nanopores.
Short chains fill slower than predicted by the Lucas-Washburn equation but long
chains fill faster. The analysis shows that the combination of the confinement
effect on the free energy of chains and the reduction of the effective radius
due to the "dead zone" slow down the imbibition. Reduction of the entanglements
is the main factor behind the reversing dynamics because of the lower effective
viscosity, which leads to a faster filling. This effect is enhanced in the
smaller capillary and more profound for longer chains. The observed increase in
the mean square radius of gyration during capillary filling provides a clear
evidence of chain orientation, which leads to the decrease in the number of
entanglements. For the scaling relation between the effective viscosity and the
degree of polymerization, we find the exponent will increase in the larger
nanopore.

Soft Condensed Matter