双层氧化石墨烯纳米体系中受限水的介电常数

为了深入了解孔径和氧化程度对介电性能的影响, 通过分子动力学模拟的方法, 探究了水在不同孔径和氧化程度的双层石墨烯纳米通道中的介电行为. 实验结果表明, 在较窄的通道环境中, 水分子会表现出更强的有序取向, 受限水的介电常数随纳米通道空间的减小而减小. 随着氧化程度的增加, 较宽的层间距对介电常数的影响大于较窄的纳米通道. 对于最宽的通道(d=1.2 nm), 石墨烯双分子层内水的介电常数随氧化程度的增加而降低, 而对于相对较窄的通道(d=0.6, 0.9 nm), 介电行为呈现出非单调的趋势. 为了理解其背后的物理原因, 分别计算了3个纳米通道的氢键数量. 结果表明, 氢键数量以及动态稳定性（对应最快的衰减率）最低的是1.2 nm宽的纳米通道, 这表明水分子在大的纳米通道中更不稳定, 同时也比在0.6和0.9 nm的纳米通道中更无序.

Dielectric Constant of Confined Water in a Bilayer Graphene Oxide Nanosystem

The properties of the dielectric constant of water in confined systems vary greatly， which has a significant impact on its applications in electrochemistry， membrane treatment and energy storage. For example， in graphene pores， the physical properties are affected by factors such as membrane pore size and degree of oxidation， but few studies have been conducted in this regard. Therefore， in order to further understand the influence of pore size and oxidation degree on the dielectric properties， molecular dynamics simulation method was used to explore the dielectric behavior of water in the double-layer graphene nanochannels with different pore size and oxidation degree. At the same time， as a local diagonal tensor in a constrained system， the dielectric constant can be defined in two directions parallel to and orthogonal to the wall. The experimental results show that water molecules exhibit a greater spatial and orientation order in a narrow environment， and the dielectric constant of confined water decreases with the decrease of the space of the nanochannels. With the increase of oxidation degree， the influence of the wider spacing on the dielectric constant is greater than that of the narrower nanochannel. For the widest channels（d=1.2 nm）， the dielectric constant of the graphene bilayer decreased with the increase of oxidation degree， while for the relatively narrow channels（d=0.6 nm， 0.9 nm）， the dielectric behavior showed a non-monotonic trend. To understand the physics behind this， we calculated the number of hydrogen bonds in the three nanochannels. The results showed that the number of hydrogen bonds and the dynamic stability（corresponding to the fastest decay rate） were the lowest at 1.2 nm， indica?ting that the water molecules were more unstable and disordered in the large nanoscale than in the 0.6 nm and 0.9 nm nanoscale. This work emphasizes the significant importance of regulating the interlamellar distance for understanding the permeance of water and its transport mechanism and provides fundamental theories for the preparation of advanced materials based on graphene oxide（GO） and their application in water treatment.