[论文解读] In-plane dielectric constant and conductivity of confined water

Bing‐Zhong Wang, M. Souilamas+11 more|arXiv (Cornell University)|Jul 31, 2024

Electrostatics and Colloid Interactions被引用 6

一句话总结

本论文使用扫描介电显微镜测量受原子级平面表面限制的水在原平面介电常数和质子电导率，厚度降至1 nm，揭示极薄水层的巨大的介电常数和高导电性，归因于无序的氢键结构。

ABSTRACT

Water is essential for almost every aspect of life on our planet and, unsurprisingly, its properties have been studied in great detail. However, disproportionately little remains known about the electrical properties of interfacial and strongly confined water where its structure deviates from that of bulk water, becoming distinctly layered. The structural change is expected to affect water's conductivity and particularly its polarizability, which in turn modifies intermolecular forces that play a crucial role in many physical and chemical processes. Here we use scanning dielectric microscopy to probe the in-plane electrical properties of water confined between atomically flat surfaces separated by distances down to 1 nm. For confinement exceeding a few nm, water exhibits an in-plane dielectric constant close to that of bulk water and its proton conductivity is notably enhanced, gradually increasing with decreasing water thickness. This trend abruptly changes when the confined water becomes only a few molecules thick. Its in-plane dielectric constant reaches giant, ferroelectric-like values of about 1,000 whereas the conductivity peaks at a few S/m, close to values characteristic of superionic liquids. We attribute the enhancement to strongly disordered hydrogen bonding induced by the few-layer confinement, which facilitates both easier in-plane polarization of molecular dipoles and faster proton exchange. This insight into the electrical properties of nanoconfined water is important for understanding many phenomena that occur at aqueous interfaces and in nanoscale pores.

研究动机与目标

• 研究强限制如何改变水在界面处的电性性质，相较于体水。
• 表征在亚纳米到数纳米厚度之间，由原子平整表面限制的水的面内介电常数和质子导电率。
• 识别极限限制下观察到的电性变化的结构原因。

提出的方法

• 使用扫描介电显微镜来探测受限水的面内电性属性。
• 在原子平整表面之间系统地将限制厚度降至1 nm。
• 随水厚度变化测量面内介电常数和质子导电率。
• 分析限制水中的氢键结构对极化和质子交换的作用。

实验结果

研究问题

• RQ1 限制厚度如何影响水的面内介电常数，相较于体水的数值？
• RQ2 在亚纳米尺度的限制下，水厚度减小时导电性如何演变？
• RQ3 哪些微观机制（例如氢键无序）推动极化和离子传输的观察到的变化？
• RQ4 是否存在一个厚度阈值，使性质从体相式转变为巨大的、铁电样的行为？

主要发现

• 当限制厚度超过数纳米时，面内介电常数接近体水值，质子导电性得到增强。
• 随着厚度减小，导电性和介电响应逐渐增强，当水仅几分子层厚时出现显著变化。
• 在少分子层范围内，面内介电常数达到约1000，导电性在几S/m时达到峰值。
• 这种增强归因于强烈的无序氢键有利于偶极极化和更快的质子交换。
• 这些发现揭示了水在纳米限域界面和纳米级孔隙中的电性特征。