Luo Kaifu, Huopaniemi Ilkka, Ala-Nissila Tapio, Ying See-Chen
Laboratory of Physics, Helsinski University of Technology, P.O. Box 1100, FIN-02015 HUT, Espoo, Finland.
J Chem Phys. 2006 Mar 21;124(11):114704. doi: 10.1063/1.2179792.
We investigate the dynamics of polymer translocation through a nanopore under an externally applied field using the two-dimensional fluctuating bond model with single-segment Monte Carlo moves. We concentrate on the influence of the field strength E, length of the chain N, and length of the pore L on forced translocation. As our main result, we find a crossover scaling for the translocation time tau with the chain length from tau approximately N2nu for relatively short polymers to tau approximately N1+nu for longer chains, where nu is the Flory exponent. We demonstrate that this crossover is due to the change in the dependence of the translocation velocity v on the chain length. For relatively short chains v approximately N-nu, which crosses over to v approximately N(-1) for long polymers. The reason for this is that with increasing N there is a high density of segments near the exit of the pore, which slows down the translocation process due to slow relaxation of the chain. For the case of a long nanopore for which R parallel, the radius of gyration Rg along the pore, is smaller than the pore length, we find no clear scaling of the translocation time with the chain length. For large N, however, the asymptotic scaling tau approximately N1+nu is recovered. In this regime, tau is almost independent of L. We have previously found that for a polymer, which is initially placed in the middle of the pore, there is a minimum in the escape time for R parallel approximately L. We show here that this minimum persists for weak fields E such that EL is less than some critical value, but vanishes for large values of EL.
我们使用具有单链节蒙特卡罗移动的二维涨落键模型，研究了在外加场作用下聚合物通过纳米孔的转移动力学。我们着重研究场强E、链长N和孔长L对强制转移的影响。作为主要结果，我们发现转移时间τ与链长之间存在交叉标度关系，对于相对较短的聚合物，τ约为N²ν，而对于较长的链，τ约为N¹⁺ν，其中ν是弗洛里指数。我们证明这种交叉是由于转移速度v对链长的依赖性发生了变化。对于相对较短的链，v约为N⁻ν，而对于长聚合物，v约为N⁻¹。其原因是随着N的增加，孔出口附近的链节密度很高，由于链的缓慢松弛，这减缓了转移过程。对于长纳米孔的情况，即沿孔的回转半径Rg小于孔长，我们没有发现转移时间与链长之间有明显的标度关系。然而，对于大的N，渐近标度关系τ约为N¹⁺ν得以恢复。在这种情况下，τ几乎与L无关。我们之前发现，对于最初放置在孔中间的聚合物，当Rg约为L时，逃逸时间存在最小值。我们在此表明，对于弱场E（即EL小于某个临界值），这个最小值仍然存在，但对于大的EL值，它会消失。
