Ion steric interactions and electrostatic correlations on electro-osmotic flow in charged nanopores with multivalent electrolytes

IF 2.5 3区 物理与天体物理 Q2 PHYSICS, FLUIDS & PLASMAS Physical Review Fluids Pub Date : 2024-07-26 DOI:10.1103/physrevfluids.9.074201
Shubhra Sahu, Bapan Mondal, Somnath Bhattacharyya
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Abstract

Atomistic and coarse-grained simulations show the formation of a condensed layer of counterions near a charged surface in contact with multivalent or monovalent electrolytes of high concentration. This condensed layer may overscreen the surface charge, and eventually a coion-dominated region may arise within the electric double layer, which again draws a layer of counterions and so on till the charge density approaches zero. Such a type of overscreening and charge density oscillation cannot be predicted through the mean-field based models as it does not account for the correlations between discrete charges. In the present study the mean-field-based model has been extended to consider the many-body interactions to analyze the electro-osmosis and ion transport of multivalent electrolytes in a highly charged nanopore. The ions are considered to be finite-sized, which is accounted for by considering the hydrodynamic steric interactions and modification of the suspension medium viscosity. Consideration of the electrostatic correlation leads to a fourth-order Poisson-Fermi equation for an electric field. Such a type of continuum model is easy to handle and to use to predict the layered structure of the EDL. Our model captures the existing experimental and molecular dynamics simulation correctly. Based on the modified model, we have analyzed the volume flow rate, current density, and ion selectivity of the pore in multivalent electrolytes for different electrostatic conditions. The present model shows that the counterion size has an impact on the condensed layer and hence overscreening. We demonstrate that the EOF reversal of multivalent electrolytes can be suppressed by mixing with monovalent slats.

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离子立体相互作用和静电相关性对多价电解质带电纳米孔内电渗流的影响
原子模拟和粗粒模拟显示,在与高浓度多价或单价电解质接触的带电表面附近,会形成一层凝聚的反离子层。这种凝聚层可能会遮蔽表面电荷,最终在电双层内形成一个以共价离子为主的区域,该区域又会吸引一层反离子,如此反复,直到电荷密度趋近于零。这种过屏蔽和电荷密度振荡无法通过基于平均场的模型来预测,因为它没有考虑离散电荷之间的相关性。在本研究中,基于均方场的模型被扩展到考虑多体相互作用,以分析多价电解质在高电荷纳米孔中的电渗和离子传输。考虑到流体力学立体相互作用和悬浮介质粘度的改变,离子被认为是有限大小的。考虑到静电相关性,可得出电场的四阶泊松-费米方程。这种连续模型易于处理,可用于预测 EDL 的分层结构。我们的模型正确捕捉了现有的实验和分子动力学模拟结果。根据修改后的模型,我们分析了多价电解质中不同静电条件下孔隙的体积流量、电流密度和离子选择性。本模型表明,反离子的大小对凝聚层有影响,因此会产生过屏蔽。我们证明,多价电解质的 EOF 反转可以通过与单价板条混合来抑制。
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来源期刊
Physical Review Fluids
Physical Review Fluids Chemical Engineering-Fluid Flow and Transfer Processes
CiteScore
5.10
自引率
11.10%
发文量
488
期刊介绍: Physical Review Fluids is APS’s newest online-only journal dedicated to publishing innovative research that will significantly advance the fundamental understanding of fluid dynamics. Physical Review Fluids expands the scope of the APS journals to include additional areas of fluid dynamics research, complements the existing Physical Review collection, and maintains the same quality and reputation that authors and subscribers expect from APS. The journal is published with the endorsement of the APS Division of Fluid Dynamics.
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