Department of Applied Physics, Aalto University, P. O. Box 11000, FI-00076 Aalto, Finland.
Department of Physics, Bilkent University, Ankara 06800, Turkey.
Phys Rev E. 2023 Mar;107(3-1):034503. doi: 10.1103/PhysRevE.107.034503.
Electrophoretic (EP) mobility reversal is commonly observed for strongly charged macromolecules in multivalent salt solutions. This curious effect takes place, e.g., when a charged polymer, such as DNA, adsorbs excess counterions so that the counterion-dressed surface charge reverses its sign, leading to the inversion of the polymer drift driven by an external electric field. In order to characterize this seemingly counterintuitive phenomenon that cannot be captured by electrostatic mean-field theories, we adapt here a previously developed strong-coupling-dressed Poisson-Boltzmann approach to the cylindrical geometry of the polyelectrolyte-salt system. Within the framework of this formalism, we derive an analytical polymer mobility formula dressed by charge correlations. In qualitative agreement with polymer transport experiments, this mobility formula predicts that the increment of the monovalent salt, the decrease of the multivalent counterion valency, and the increase of the dielectric permittivity of the background solvent suppress charge correlations and increase the multivalent bulk counterion concentration required for EP mobility reversal. These results are corroborated by coarse-grained molecular dynamics simulations showing how multivalent counterions induce mobility inversion at dilute concentrations and suppress the inversion effect at large concentrations. This re-entrant behavior, previously observed in the aggregation of like-charged polymer solutions, calls for verification by polymer transport experiments.
电泳（EP）迁移率反转在多价盐溶液中带强电荷的大分子中很常见。这种奇特的效应发生在带电荷的聚合物（如 DNA）吸附过量抗衡离子时，导致抗衡离子包裹的表面电荷反转其符号，从而导致外部电场驱动的聚合物漂移反转。为了描述这种看似违反直觉的现象，我们无法用静电平均场理论来解释，我们在这里将之前开发的强耦合包裹的泊松-玻尔兹曼方法应用于聚合物-盐系统的圆柱几何形状。在这个形式框架内，我们推导出一个由电荷相关项包裹的聚合物迁移率公式。与聚合物输运实验定性一致，这个迁移率公式预测单价盐的增加、多价抗衡离子价数的减少和背景溶剂介电常数的增加都会抑制电荷相关项，并增加 EP 迁移率反转所需的多价体相抗衡离子浓度。粗粒化分子动力学模拟结果证实了这些结果，表明多价抗衡离子如何在稀释浓度下诱导迁移率反转，并在高浓度下抑制反转效应。这种再进入行为，以前在类似电荷聚合物溶液的聚集中观察到，需要通过聚合物输运实验来验证。
