Córdoba Andrés, Montes de Oca Joan Manuel, Darling Seth B, de Pablo Juan J
Pritzker School of Molecular Engineering, University of Chicago, Chicago, Illinois 60637, United States.
Advanced Materials for Energy-Water Systems (AMEWS) Energy Frontier Research Center, Argonne National Laboratory, Lemont, Illinois 60439, United States.
ACS Nano. 2024 May 14;18(19):12569-12579. doi: 10.1021/acsnano.4c03546. Epub 2024 May 2.
In this paper, we investigate how the dielectric constant, ϵ, of an electrolyte solvent influences the current rectification characteristics of bipolar nanopores. It is well recognized that bipolar nanopores with two oppositely charged regions rectify current when exposed to an alternating electric potential difference. Here, we consider dilute electrolytes with NaCl only and with a mixture of NaCl and charged nanoparticles. These systems are studied using two levels of description, all-atom explicit water molecular dynamics (MD) simulations and coarse-grained implicit solvent MD simulations. The charge density and electric potential profiles and current-voltage relationship predicted by the implicit solvent simulations with ϵ = 11.3 show good agreement with the predictions from the explicit water simulations. Under nonequilibrium conditions, the predictions of the implicit solvent simulations with a dielectric constant closer to the one of bulk water are significantly different from the predictions obtained with the explicit water model. These findings are closely aligned with experimental data on the dielectric constant of water when confined to nanometric spaces, which suggests that ϵ decreases significantly compared to its value in the bulk. Moreover, the largest electric current rectification is observed in systems containing nanoparticles when ϵ = 78.8. Using enhanced sampling, we have shown that this larger rectification arises from the presence of a significantly deeper minimum in the free energy of the system with a larger ϵ, and when a negative voltage bias is applied. Since implicit solvent models and mean-field continuum theories are often used to design Janus membranes based on bipolar nanopores, this work highlights the importance of properly accounting for the effects of confinement on the dielectric constant of the electrolyte solvent. The results presented here indicate that the dielectric constant in implicit solvent simulations may be used as an adjustable parameter to approximately account for the effects of nanometric confinement on aqueous electrolyte solvents.
在本文中，我们研究了电解质溶剂的介电常数ϵ如何影响双极纳米孔的电流整流特性。众所周知，具有两个相反电荷区域的双极纳米孔在暴露于交变电势差时会使电流整流。在此，我们考虑仅含有NaCl以及含有NaCl和带电纳米颗粒混合物的稀电解质。使用全原子显式水分子动力学（MD）模拟和粗粒化隐式溶剂MD模拟这两种描述层次对这些体系进行了研究。介电常数ϵ = 11.3的隐式溶剂模拟所预测的电荷密度、电势分布以及电流 - 电压关系与显式水模拟的预测结果显示出良好的一致性。在非平衡条件下，介电常数更接近本体水的隐式溶剂模拟的预测结果与显式水模型得到的预测结果有显著差异。这些发现与水在纳米空间中受限情况下介电常数的实验数据密切相关，这表明与本体中的值相比，ϵ显著降低。此外，当ϵ = 78.8时，在含有纳米颗粒的体系中观察到最大的电流整流。通过增强采样，我们表明这种更大的整流源于系统自由能中存在一个显著更深的最小值，该最小值出现在ϵ较大且施加负电压偏置时。由于隐式溶剂模型和平均场连续介质理论经常被用于基于双极纳米孔设计Janus膜，这项工作突出了正确考虑受限对电解质溶剂介电常数影响的重要性。此处给出的结果表明，隐式溶剂模拟中的介电常数可作为一个可调参数，以近似考虑纳米受限对水性电解质溶剂的影响。
