Huopaniemi Ilkka, Luo Kaifu, Ala-Nissila Tapio, Ying See-Chen
Laboratory of Physics, Helsinki University of Technology, P.O. Box 1100, FIN-02015 HUT Espoo, Finland.
J Chem Phys. 2006 Sep 28;125(12):124901. doi: 10.1063/1.2357118.
We investigate the dynamics of polymer translocation through a nanopore using two-dimensional Langevin dynamics simulations. In the absence of an external driving force, we consider a polymer which is initially placed in the middle of the pore and study the escape time tau(e) required for the polymer to completely exit the pore on either side. The distribution of the escape times is wide and has a long tail. We find that tau(e) scales with the chain length N as tau(e) approximately N(1+2nu), where nu is the Flory exponent. For driven translocation, we concentrate on the influence of the friction coefficient xi, the driving force E, and the length of the chain N on the translocation time tau, which is defined as the time duration between the first monomer entering the pore and the last monomer leaving the pore. For strong driving forces, the distribution of translocation times is symmetric and narrow without a long tail and tau approximately E(-1). The influence of xi depends on the ratio between the driving and frictional forces. For intermediate xi, we find a crossover scaling for tau with N from tau approximately N(2nu) for relatively short chains to tau approximately N(1+nu) for longer chains. However, for higher xi, only tau approximately N(1+nu) is observed even for short chains, and there is no crossover behavior. This result can be explained by the fact that increasing xi increases the Rouse relaxation time of the chain, in which case even relatively short chains have no time to relax during translocation. Our results are in good agreement with previous simulations based on the fluctuating bond lattice model of polymers at intermediate friction values, but reveal additional features of dependency on friction.
我们使用二维朗之万动力学模拟研究了聚合物通过纳米孔的转位动力学。在没有外部驱动力的情况下，我们考虑一种最初放置在孔中间的聚合物，并研究聚合物完全从孔的任一侧退出所需的逃逸时间(\tau_e)。逃逸时间的分布很宽且有一个长尾。我们发现(\tau_e)与链长(N)的标度关系为(\tau_e\approx N^{1 + 2\nu})，其中(\nu)是弗洛里指数。对于驱动转位，我们关注摩擦系数(\xi)、驱动力(E)和链长(N)对转位时间(\tau)的影响，转位时间定义为第一个单体进入孔到最后一个单体离开孔的持续时间。对于强驱动力，转位时间的分布是对称且狭窄的，没有长尾，且(\tau\approx E^{-1})。(\xi)的影响取决于驱动力与摩擦力的比值。对于中等的(\xi)，我们发现(\tau)与(N)的标度关系存在交叉，对于相对短的链，(\tau\approx N^{2\nu})，对于较长的链，(\tau\approx N^{1 + \nu})。然而，对于更高的(\xi)，即使是短链也只观察到(\tau\approx N^{1 + \nu})，并且没有交叉行为。这一结果可以通过增加(\xi)会增加链的劳斯松弛时间这一事实来解释，在这种情况下，即使是相对短的链在转位过程中也没有时间松弛。我们的结果与基于聚合物波动键晶格模型在中等摩擦值下的先前模拟结果非常吻合，但揭示了对摩擦依赖性的其他特征。
