Agrawal Nikhil R, Duan Chao, Wang Rui
Department of Chemical and Biomolecular Engineering, University of California, Berkeley, Berkeley, California 94720-1462, United States.
Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.
J Phys Chem B. 2024 Jan 11;128(1):303-311. doi: 10.1021/acs.jpcb.3c04739. Epub 2023 Dec 27.
Understanding overcharging and charge inversion is one of the long-standing challenges in soft matter and biophysics. To study these phenomena, we employ the modified Gaussian renormalized fluctuation theory, which allows for the self-consistent accounting of spatially varying ionic strength as well as the spatial variations in dielectric permittivity and excluded volume effects. The underlying dependence of overcharging on the electrostatic coupling is elucidated by varying the surface charge, counterion valency, and dielectric contrast. Consistent with simulations, three characteristic regimes corresponding to weak, moderate, and strong coupling are identified. Important features like the inversion of zeta potential, crowding, and ionic layering at the surface are successfully captured. For weak coupling, there is no overcharging. In the moderate coupling regime, overcharging increases with the surface charge. Finally, in the strong coupling regime, ionic crowding and saturation in overcharging are observed. Our theory predicts a nonmonotonic dependence of charge inversion on multivalent salt concentration as well as the addition of monovalent salt, in quantitative agreement with experiments.
理解过充电和电荷反转是软物质和生物物理学中长期存在的挑战之一。为了研究这些现象，我们采用了修正的高斯重整化涨落理论，该理论能够自洽地考虑空间变化的离子强度以及介电常数和排除体积效应的空间变化。通过改变表面电荷、抗衡离子价数和介电对比度，阐明了过充电对静电耦合的潜在依赖性。与模拟结果一致，确定了对应于弱、中和强耦合的三个特征区域。成功捕捉到了诸如表面ζ电位反转、拥挤和离子分层等重要特征。对于弱耦合，不存在过充电现象。在中等耦合区域，过充电随表面电荷增加。最后，在强耦合区域，观察到离子拥挤和过充电饱和现象。我们的理论预测了电荷反转对多价盐浓度以及单价盐添加的非单调依赖性，与实验结果在定量上一致。
