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Nonreciprocal interactions induced by water in confinement
Physical Review Research Pub Date : 2020-11-17 , DOI: 10.1103/physrevresearch.2.043244
Felipe Jiménez-Ángeles , Katherine J. Harmon , Trung Dac Nguyen , Paul Fenter , Monica Olvera de la Cruz

Water mediates electrostatic interactions via the orientation of its dipoles around ions, molecules, and interfaces. This induced water polarization consequently influences multiple phenomena. In particular, water polarization affects ion adsorption and transport, biomolecular self-assembly, and surface chemical reactions. Therefore, it is of paramount importance to understand water-mediated interactions modulated by nanoconfinement at the nanoscale. Here we investigate the effective interaction between two oppositely charged ions in different positions in water confined between two graphene surfaces. We find that the attraction between physisorbed ions is enhanced in the surface normal direction while the in-plane interaction is almost unaffected. The attraction in the surface normal direction is further enhanced by decreasing the confinement distance. Conversely, when one ion is intercalated into the graphene layers, the interaction becomes repulsive. Moreover, upon exchange of the ions' positions along the surface normal direction, the interaction energy changes by about 5kBT. The nonequivalent and directional properties found here, referred to as nonreciprocal interactions, cannot be explain by current water permittivity models in confinement. Our x-ray reflectivity experiments of the water structure near a graphene surface support our molecular dynamics simulation results. Our work shows that the water structure is not enough to infer electrostatic interactions near interfaces.

中文翻译:

禁闭水引起的不可逆相互作用

水通过偶极子围绕离子,分子和界面的取向来介导静电相互作用。因此,这种水极化会影响多种现象。特别是水的极化会影响离子的吸附和传输,生物分子的自组装以及表面化学反应。因此,最重要的是了解在纳米尺度上由纳米限制作用调节的水介导的相互作用。在这里,我们研究了两个石墨烯表面之间的水中不同位置的两个带相反电荷的离子之间的有效相互作用。我们发现,物理吸附离子之间的吸引力沿表面法线方向增强,而平面内相互作用几乎不受影响。通过减小限制距离,可以进一步增强表面法线方向上的吸引力。相反,当一个离子插入到石墨烯层中时,相互作用变得排斥。此外,在沿表面法线方向交换离子位置时,相互作用能的变化约为5ķŤ。此处发现的非等价性和方向性称为不可逆相互作用,不能用目前的水介电常数模型加以解释。我们在石墨烯表面附近的水结构的X射线反射率实验支持我们的分子动力学模拟结果。我们的工作表明,水的结构不足以推断界面附近的静电相互作用。
更新日期:2020-11-17
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