Water-based nanofluidic devices, where water is confined in Angstrom scale nanochannels, are widely encountered in nanotechnology. Although it is known that the material of confinement has a significant influence on the properties of confined water, much less is known of the relationship between the structure of nanoconfined water and its properties, impacting the design of nanofluidic devices. We explore the behavior of a confined water monolayer within a bilayer molybdenum disulfide (MoS₂) structure, comparing its behavior with that within bilayer graphene. We find that only ∼2% of the entire structure has nearly perfect square order and the rest is filled with rhombus ordering. Surprisingly, we find that although the structure of monolayer confined water remains the same in both the 2D materials, thermodynamic analysis shows that confined water has a more favorable potential environment in MoS₂ than graphene for all twists explored here. However, with increasing twist angle, the encapsulating effect of water diminishes slightly in the case of graphene than MoS₂. Interestingly, the dielectric constant is anomalously lower in MoS₂ by ∼22% compared to the confined water dielectric constant in a graphene nanochannel. Finally, we show that the static friction coefficient of confined water in bilayer MoS₂ does not change with twist. However, unlike graphene, it does not show an order of magnitude reduction due to this extreme confinement. Overall, we show, counter-intuitively, that although confined water structures are similar in different 2D materials considered here, there exist differences in other properties of this structured water.

中文翻译：

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扭曲 2D 材料中受限水的结构相似但热力学、介电和摩擦特性不同：MoS2 与石墨烯


水基纳米流体器件，其中水被限制在埃级纳米通道中，在纳米技术中被广泛使用。尽管已知约束材料对约束水的性能有重大影响，但对纳米约束水的结构与其特性之间的关系知之甚少，从而影响了纳米流体器件的设计。我们探讨了双层二硫化钼 （MoS₂） 结构中平静水单层的行为，将其行为与双层石墨烯中的行为进行了比较。我们发现整个结构中只有 ∼2% 具有近乎完美的平方顺序，其余部分由菱形顺序填充。令人惊讶的是，我们发现，尽管单层承压水的结构在两种 2D 材料中保持不变，但热力学分析表明，对于此处探讨的所有扭曲，承压水在 MoS₂ 中具有比石墨烯更有利的势环境。然而，随着扭曲角的增加，石墨烯的包封作用比 MoS₂ 略有减弱。有趣的是，与石墨烯纳米通道中的受限水介电常数相比，MoS₂ 中的介电常数异常低约 22%。最后，我们表明双层 MoS₂ 中承压水的静摩擦系数不随扭曲而变化。然而，与石墨烯不同的是，由于这种极端的限制，它不会显示出数量级的降低。总的来说，我们反直觉地表明，尽管这里考虑的不同 2D 材料中的承压水结构相似，但这种结构水的其他属性存在差异。