Polymer translocation through a nanopore under a pulling force

We investigate polymer translocation through a nanopore under a pulling force using Langevin dynamics simulations. We concentrate on the influence of the chain length $N$ and the pulling force $F$ on the translocation time $\tau$. The distribution of $\tau$ is symmetric and narrow for strong $F$. We find that $\tau \sim N^2$ and translocation velocity $v\sim N^{-1}$ for both moderate and strong $F$. For infinitely wide pores, three regimes are observed for $\tau$ as a function of $F$. With increasing $F$, $\tau$ is independent of $F$ for weak $F$, and then $\tau \sim F^{-2+{\nu }^{-1}}$ for moderate $F$, where $\nu$ is the Flory exponent, which finally crosses over to $\tau \sim F^{-1}$ for strong force. For narrow pores, even for moderate force $\tau \sim F^{-1}$. Finally, the waiting time, for monomer $s$ and monomer $s+1$ to exit the pore, has a maximum for $s$ close to the end of the chain, in contrast to the case where the polymer is driven by an external force within the pore.

Figure 1

A typical configuration of a polymer of length $N=300$ pulled by a force of strength $F=5$ during translocation process.

Figure 2

The distribution of 2000 translocation times for a chain of length $N=100$ under the pulling force of strength $F=5$. Here, the translocation times are normalized by their average value.

Figure 3

Waiting times for a polymer of length (a) $N=100$ and (b) $N=300$ with $F=5$.

Figure 4

The translocation time as a function of polymer length $N$ for (a) an infinitely wide pore and (b) a pore of finite width. A constant pulling force of strength $F=0.5$ and 5 acts on the first monomer.

Figure 5

Translocation time as a function of pulling force strength for (a) an infinitely wide pore and (b) a pore of finite width. $\tau$ is an average of 1000 runs. Here, $N=100$.