Refractive index of nanoconfined water reveals its anomalous physical properties
Refractive index of nanoconfined water reveals its anomalous physical properties
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DOI：
10.1039/d0nh00180e
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发表时间：
2020-06-01
影响因子：
9.7
通讯作者：
Tanaka, T.
中科院分区：
文献类型：
--
作者：
Le, T. H. H.;Morita, A.;Tanaka, T.
尽管对限制在纳米空间中的水的独特性质进行了广泛的研究，但限制效应中所涉及的长度尺度的潜在机制和意义仍然是有争议的主题。特别是介电常数和折射率是模拟和理解纳米承压水的关键参数，但缺乏实验证据。我们报告的水的折射率的测量在10-100 nm的空间，通过利用水的限制和局部表面等离子体在物理化学定义良好的纳米腔。结果表明，承压水的面外折射率n（垂直于）的值显着较低，并具有标度行为。这是由于氢键网络的加强促进了界面极化的抑制和电子极化的长程相关。利用折射率作为传感探针，我们还观察到了水结构在很宽的温度范围内的异常稳定性。我们的测量结果为基准水模型和纳米约束下的分子相互作用提供了重要的反馈信息。这项研究还开辟了一种使用等离子体共振来表征纳米限制分子和化学反应的新方法，从而使我们对限制效应有了基本的了解。
Despite extensive studies on the distinctive properties of water confined in a nanospace, the underlying mechanism and significance of the lengthscale involved in the confinement effects are still subjects of controversy. The dielectric constant and the refractive index in particular are key parameters in modeling and understanding nanoconfined water, yet experimental evidence is lacking. We report the measurement of the refractive indices of water in 10-100 nm spaces by exploiting the confinement of water and localized surface plasmons in a physicochemically well-defined nanocavity. The results revealed significantly low values and the scaling behavior of the out-of-plane refractive index n(perpendicular to) of confined water. They are attributed to the polarization suppression at the interfaces and the long-range correlation in electronic polarization facilitated by the strengthened H-bonding network. Using the refractive index as a sensing probe, we also observed anomalous stability of water structures over a wide range of temperature. Our measurement results provide essential feedback information for benchmarking water models and molecular interactions under nanoconfinement. This study also opens up a new methodology of using plasmon resonance in characterizing nanoconfined molecules and chemical reactions, and thus gives us fundamental insight into confinement effects.