Xie Yanbo, Fu Li, Niehaus Thomas, Joly Laurent
MOE Key Laboratory of Material Physics and Chemistry under Extraordinary Conditions, School of Physical Science and Technology, Northwestern Polytechnical University, Xian, 710072, China.
Univ Lyon, Ecole Centrale de Lyon, Laboratoire de Tribologie et Dynamique des Systèmes, UMR 5513, 36 avenue Guy de Collongue, 69134 Ecully Cedex, France.
Phys Rev Lett. 2020 Jul 3;125(1):014501. doi: 10.1103/PhysRevLett.125.014501.
Nanofluidic systems show great promise for applications in energy conversion, where their performance can be enhanced by nanoscale liquid-solid slip. However, efficiency is also controlled by surface charge, which is known to reduce slip. Combining molecular dynamics simulations and analytical developments, we show the dramatic impact of surface charge distribution on the slip-charge coupling. Homogeneously charged graphene exhibits a very favorable slip-charge relation (rationalized with a new theoretical model correcting some weaknesses of the existing ones), leading to giant electrokinetic energy conversion. In contrast, slip is strongly affected on heterogeneously charged surfaces, due to the viscous drag induced by counterions trapped on the surface. In that case slip should depend on the detailed physical chemistry of the interface controlling the fraction of bound ions. Our numerical results and theoretical models provide new fundamental insight into the molecular mechanisms of liquid-solid slip, and practical guidelines for searching new functional interfaces with optimal energy conversion properties, e.g., for blue energy or waste heat harvesting.
纳米流体系统在能量转换应用中展现出巨大潜力，其性能可通过纳米级液固滑移得到增强。然而，效率也受表面电荷控制，已知表面电荷会降低滑移。结合分子动力学模拟和分析进展，我们展示了表面电荷分布对滑移 - 电荷耦合的显著影响。均匀带电的石墨烯表现出非常有利的滑移 - 电荷关系（用一个纠正了现有模型一些弱点的新理论模型进行了合理化解释），从而实现巨大的动电能量转换。相比之下，由于捕获在表面的反离子引起的粘性阻力，在异质带电表面上滑移会受到强烈影响。在这种情况下，滑移应取决于控制结合离子分数的界面的详细物理化学性质。我们的数值结果和理论模型为液固滑移的分子机制提供了新的基本见解，并为寻找具有最佳能量转换特性的新功能界面提供了实用指导方针，例如用于蓝能或废热收集。
