Detailed Computational Study of Translocation Dynamics: Revealing the Physical Mechanisms of Viscosity Dependent Scaling Laws

Noting the limitations of current methods of characterizing the unbiased translocation of a polymer through a nanopore, we demonstrate a measurement which more completely maps out the process in time. Applying this approach to Langevin Dynamics simulations of translocation at different viscosities for a relatively tight nanopore yields interesting results for the scaling of the translocation time with polymer length: $\tau \sim N^\alpha$. At low viscosities, super-diffusive results are obtained. At high viscosities, while translocation is found to obey simple scaling with $\alpha=2.2$ near the beginning of the process, length dependent deviations from simple scaling near the end result in an overall $\alpha$ exponent which is viscosity dependent. The memory and entropic effects giving rise to this behaviour will be discussed.