Capillary Filling of Polymer Chains in Nanopores

We performed molecular dynamics simulations with a coarse-grained model to investigate the capillary filling dynamics of polymer chains in a nanopore. Short chains fill slower than predicted by the Lucas-Washburn Equation but long chains fill faster. The analysis shows that a viscous area is generated by the strong adsorption of polymer chains next to the pore walls that reduces the pore radius and slows down imbibition. This region can be negligible at the macroscopic scale but cannot be ignored at the nanoscale. Reduction of the entanglements is the main factor behind the reversing dynamics because it induces a lower effective viscosity and leads to a faster filling. This effect is enhanced for longer chains. The observed increase in the mean square radius of gyration during capillary filling provides a clear evidence of chain orientation, that leads to the decrease in the number of entanglements. Finally, we propose an equation that accounts for the effect of chain length on the capillary filling dynamics of polymer chains in nanopores.