Profile of the Static Permittivity Tensor of Water at Interfaces: Consequences for Capacitance, Hydration Interaction and Ion Adsorption
Profile of the Static Permittivity Tensor of Water at Interfaces: Consequences for Capacitance, Hydration Interaction and Ion Adsorption
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DOI：
10.1021/la2051564
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发表时间：
2012-05-22
期刊：
影响因子：
3.9
通讯作者：
Netz, Roland R.
中科院分区：
文献类型：
--
作者：
Bonthuis, Douwe Jan;Gekle, Stephan;Netz, Roland R.
我们推导出理论框架来计算介电响应张量，并使用分子动力学模拟确定亲水和疏水表面附近的水的成分。对于所使用的非极化水模型，线性响应理论被发现适用于类似于 2 V/nm 的外部垂直场强，这远远超出了实验介电击穿阈值。偶极子贡献主导平行于界面的介电响应，而对于垂直分量，必须保留四极和八极项。在单个带电界面的离子分布的平均场描述中包括空间相关的介电函数，我们重现了界面电容的实验值。同时，介电函数降低了两个带电表面之间分离压力的静电部分，这与之前认为的不同。亲水表面和疏水表面之间的界面极化率差异可以用介电分割表面来量化。使用介电分割表面和吉布斯分割表面位置来估计靠近界面的单个离子的自由能，发现离子特异性吸附效应在疏水表面比在亲水表面更明显，与实验趋势一致。
We derive the theoretical framework to calculate the dielectric response tensor and determine its components for water adjacent to hydrophilic and hydrophobic surfaces using molecular dynamics simulations. For the nonpolarizable water model used, linear response theory is found to be applicable up to an external perpendicular field strength of similar to 2 V/nm, which is well beyond the experimental dielectric breakdown threshold. The dipole contribution dominates the dielectric response parallel to the interface, whereas for the perpendicular component it is essential to keep the quadrupole and octupole terms. Including the space-dependent dielectric function in a mean-field description of the ion distribution at a single charged interface, we reproduce experimental values of the interfacial capacitance. At the same time, the dielectric function decreases the electrostatic part of the disjoining pressure between two charged surfaces, unlike previously thought. The difference in interfacial polarizability between hydrophilic and hydrophobic surfaces can be quantized in terms of the dielectric dividing surface. Using the dielectric dividing surface and the Gibbs dividing surface positions to estimate the free energy of a single ion close to an interface, ion-specific adsorption effects are found to be more pronounced at hydrophobic surfaces than at hydrophilic surfaces, in agreement with experimental trends.