Polyelectrolyte Translocation through a Finite Length Nanopore: Interplay of Slip, Applied Potential and Hydrodynamics

We use a combination of molecular dynamics simulations and computational fluid dynamics to discern the effect of enthalpic and entropic contribution towards polyelectrolyte translocation in a finite length nanopore. We consider the electrophoretic transport of a single chain charged polymer through a nanopore under the influence of an applied electric field. The confinement and the fluid-solid interaction at the surface of the polyelectrolyte results in a relative slip of the fluid molecules and ions at the nanopore-fluid interface and polyelectrolyte-fluid interface, respectively. Moreover, the translocating charged interface leads to development of an electric double layer which evolves with the position of the polyelectrolyte in the pore and tweaks the induced potential both in the axial and transverse direction due to ion concentration polarization and ion partitioning effect. Thus, the resultant dynamics is a complex concoction of the fluid-solid hydrodynamic interactions at polyelectrolyte and pore wall, the electrostatic interactions in the pore and the structural/entropic interactions of the polyelectrolyte. We observe that polyelectrolyte which otherwise fails enter the nanopore by virtue induced potential, successfully translocate due to slip and enhanced applied potential. An increase in length of polyelectrolyte also enhances the charge and counter-ion accumulation increasing likelihood of successful translocation.