Using an incremental mean first passage approach to explore the viscosity dependent dynamics of the unbiased translocation of a polymer through a nanopore

Noting the limitations of the standard characterization of translocation dynamics, an incremental mean first passage process methodology is used to more completely map the unbiased translocation of a polymer through a nanopore. In this approach, the average time t(0) required to reach successively increasing displacements for the first time is recorded - a measure shown to be more commensurate with the mean first passage nature of translocation. Applying this methodology to the results of Langevin dynamics simulations performed in three dimensions across a range of viscosities, a rich set of dynamics spanning regular diffusion at low viscosities to sub-diffusion at higher viscosities is revealed. Further, while the scaling of the net translocation time tau with polymer length N is shown to be viscosity-dependent, common regimes are found across all viscosities: super-diffusive behaviour at short times, an N-independent backbone consistent with tau similar to N-2.0 at low viscosities and tau similar to N-2.2 at higher viscosities for intermediate times, and N-dependent deviations from the backbone near the completion of translocation. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4711865]