Simulation Study of Polyelectrolyte Translocation through a Nanopore in Monovalent and Divalent Salt Solutions

Pai-Yi Hsiao^1*

¹Department of Engineering and System Science, National Tsing Hua University, Hsinchu, Taiwan

* Presenter:Pai-Yi Hsiao, email:pyhsiao@ess.nthu.edu.tw

We study the central question asked in the research domain of polymer translocation: how does the mean translocation time scale with the chain length N and the transmembrane field strength E? First, the Sakaue’s scaling theory for polymer translocation is re-derived. The driving fields are distinguished into four force regimes, the unbiased (UB) regime, the weakly-driven (WD) regime, the strongly-driven trumpet (SD(T)) regime and the strongly-driven isoflux (SD(I)) regime. Langevin dynamics simulations are then performed to verify the theory. We simulate charged polymers driven through a nanopore in the presence of monovalent and divalent counterions in the solutions. The field strength E is varied over a wide range of magnitude to cover the four characteristic force regimes. By changing the chain length, the mean translocation time is shown to follow the scaling behavior <τ>~N^α E^-δ. The exponents α and δ are calculated in each force regime. Both of them vary with N and E and, hence, are not universal in the parameter’s space. We investigate further the diffusion behavior of translocation. The subdiffusion exponent γ_p is extracted. The three key exponents ν_s, q, z_p are then obtained from the simulations. Together with γ_p, the validness of the scaling theory is verified. Through a comparison with experiments, the location of a usual experimental condition is pointed out on the scaling plot. (This research is funded by the Ministry of Science and Technology, Taiwan, grant number MOST 106-2112-M-007-027-MY3.)

Keywords: polymer translocation, polyelectrolyte, scaling theory, molecular dynamics simulations