Polson James M, Zhu Qinxin
Department of Physics, University of Prince Edward Island, 550 University Avenue, Charlottetown, Prince Edward Island C1A 4P3, Canada.
Phys Rev E. 2021 Jan;103(1-1):012501. doi: 10.1103/PhysRevE.103.012501.
Polymers confined to a narrow channel are subject to strong entropic forces that tend to drive the molecules apart. In this study, we use Monte Carlo computer simulations to study the segregation behavior of two flexible hard-sphere polymers under confinement in a cylindrical channel. We focus on the effects of using polymers of different lengths. We measure the variation of the conformational free energy, F, with the center-of-mass separation distance, λ. The simulations reveal four different separation regimes, characterized by different scaling properties of the free energy with respect to the polymer lengths and the channel diameter, D. We propose a regime map in which the state of the system is determined by the values of the quantities N_{2}/N_{1} and λ/(N_{1}+N_{2})D^{-β}, where N_{1} and N_{2} are the polymer lengths, and where β≈0.64. The observed scaling behavior of F(λ) in each regime is in reasonable agreement with predictions using a simple theoretical model. In addition, we use MC dynamics simulations to study the segregation dynamics of initially overlapping polymers by measurement of the incremental mean first-passage time with respect to λ. For systems characterized by a wide range of λ in which a short polymer is nested within a longer one, the segregation dynamics are close to that expected for two noninteracting one-dimensional random walkers undergoing unbiased diffusion. When the free-energy gradient is large, segregation is rapid and characterized by out-of-equilibrium effects.
限制在狭窄通道内的聚合物会受到强大的熵力作用，这些力往往会使分子相互分离。在本研究中，我们使用蒙特卡罗计算机模拟来研究两种柔性硬球聚合物在圆柱形通道限制下的分离行为。我们重点关注使用不同长度聚合物的影响。我们测量构象自由能F随质心分离距离λ的变化。模拟揭示了四种不同的分离区域，其特征在于自由能相对于聚合物长度和通道直径D具有不同的标度性质。我们提出了一个区域图，其中系统状态由量N₂/N₁和λ/(N₁ + N₂)D⁻ᵝ的值决定，其中N₁和N₂是聚合物长度，且β≈0.64。在每个区域中观察到的F(λ)的标度行为与使用简单理论模型的预测合理吻合。此外，我们使用蒙特卡罗动力学模拟，通过测量相对于λ的增量平均首次通过时间来研究初始重叠聚合物的分离动力学。对于以宽范围的λ为特征的系统，其中短聚合物嵌套在长聚合物内，分离动力学接近于两个非相互作用的一维随机漫步者进行无偏扩散时的预期情况。当自由能梯度较大时，分离迅速且具有非平衡效应的特征。
