Simulation Study of Polyelectrolyte Translocation through a Nanopore in Monovalent and Divalent Salt Solutions
Pai-Yi Hsiao1*
1Department of Engineering and System Science, National Tsing Hua University, Hsinchu, Taiwan
* Presenter:Pai-Yi Hsiao,
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>~Nα E. 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 γp is extracted. The three key exponents νs, q, zp are then obtained from the simulations. Together with γp, 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