Translocation of Charged Polymers through a Nanopore in Monovalent and Divalent Salt Solutions: A Scaling Study Exploring over the Entire Driving Force Regimes

Langevin dynamics simulations are performed to study polyelectrolytes driven through a nanopore in monovalent and divalent salt solutions. The driving electric field E is applied inside the pore, and the strength is varied to cover the four characteristic force regimes depicted by a rederived scaling theory, namely the unbiased (UB) regime, the weakly-driven (WD) regime, the strongly-driven trumpet (SD(T)) regime and the strongly-driven isoflux (SD(I)) regime. By changing the chain length N, the mean translocation time is studied under the scaling form $⟨\tau ⟩\sim N^{\alpha }{E}^{-\delta }$ . The exponents $\alpha$ and $\delta$ are calculated in each force regime for the two studied salt cases. Both of them are found to vary with E and N and, hence, are not universal in the parameter’s space. We further investigate the diffusion behavior of translocation. The subdiffusion exponent ${\gamma }_{\mathrm{p}}$ is extracted. The three essential exponents ${\nu }_{\mathrm{s}}$ , q, $z_{\mathrm{p}}$ are then obtained from the simulations. Together with ${\gamma }_{\mathrm{p}}$ , the validness of the scaling theory is verified. Through a comparison with experiments, the location of a usual experimental condition on the scaling plot is pinpointed.