Wang Yanlei, Wang Chenlu, Zhang Yaqin, Huo Feng, He Hongyan, Zhang Suojiang
Beijing Key Laboratory of Ionic Liquids Clean Process, CAS Key Laboratory of Green Process and Engineering, State Key Laboratory of Multiphase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences, Beijing, 100190, China.
Small. 2019 Jul;15(29):e1804508. doi: 10.1002/smll.201804508. Epub 2019 Jan 25.
The understanding of confined structure and flow property of ionic liquid (IL) in a nanochannel are essential for the efficient application of ILs in the green chemical processes. In this work, the ionic structure and various flow behaviors of ILs inside graphene nanochannels via molecular dynamics simulations are shown. The effect of the nanochannel structure on confined flow is explored, showing that the width mainly heightens the viscosity while the oxidation degree primarily enhances the interfacial friction coefficient. Tuning the width and oxidation degree of nanochannel, three different flow behaviors including Poiseuille, partial plunger and full plunger flow can be achieved, where the second one does not occur in water or other organic solvents. To describe the special flow behavior, an effective influence extent of the nanochannel (w ) is defined, whose value can distinguish the above flows effectively. Based on w , the phase diagrams of flow behavior for the nanochannel structure and pressure gradient are obtained, showing that the critical pressure gradient decreases with width and increases with the oxidation degree. Based on the quantitative relations between confined structures, viscosity, friction coefficient, flow behavior, and nanochannel structure, the intrinsic mechanism of regulating the flow behavior and rational design of nanochannel are finally discussed.
理解离子液体（IL）在纳米通道中的受限结构和流动特性对于ILs在绿色化学过程中的高效应用至关重要。在这项工作中，通过分子动力学模拟展示了石墨烯纳米通道内ILs的离子结构和各种流动行为。探讨了纳米通道结构对受限流动的影响，结果表明宽度主要增加了粘度，而氧化程度主要提高了界面摩擦系数。通过调节纳米通道的宽度和氧化程度，可以实现包括泊肃叶流、部分柱塞流和全柱塞流在内的三种不同流动行为，其中第二种在水或其他有机溶剂中不会出现。为了描述这种特殊的流动行为，定义了纳米通道的有效影响程度（w ），其值可以有效区分上述流动。基于w ，获得了纳米通道结构和压力梯度的流动行为相图，结果表明临界压力梯度随宽度减小而增加，随氧化程度增加而增加。基于受限结构、粘度、摩擦系数、流动行为和纳米通道结构之间的定量关系，最终讨论了调节流动行为的内在机制和纳米通道的合理设计。
