While many mechanistic studies have focused on the lubricious properties of ionic liquids (ILs) on ideally smooth surfaces, little is known about the mechanisms by which ILs lubricate contacts with nanoscale roughness. Here, substrates with controlled density of nanoparticles are prepared to examine the influence of nanoscale roughness on the lubrication by 1‐hexyl‐3‐methyl imidazolium bis(trifluoromethylsulfonyl)imide. Atomic force microscopy is employed to investigate adhesion, hydrodynamic slip, and friction at the lubricated contact as a function of surface topography for the first time. This study reveals that nanoscale roughness has a significant influence on the slip along the surface and leads to a maximum slip length on the substrates with intermediate nanoparticle density. This coincides with the minimum friction coefficient at sufficiently small contact stresses, likely due to the lower resistance of the IL film to shear. However, at the higher pressures applied with a sharp tip, friction increases with nanoparticle density, indicating that the IL is not able to alleviate the increased dissipation due to roughness. The results of this work point toward a complex influence of the surface topology on friction. This study can help design ILs and nanopatterned substrates for tribological applications and nano‐ and microfluidics.

中文翻译：

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纳米粗糙度对离子液体润滑行为的影响

尽管许多机理研究集中在理想光滑表面上离子液体（IL）的润滑特性上，但对ILs润滑纳米级粗糙度接触的机理了解甚少。在这里，准备了具有受控纳米颗粒密度的基材，以检查纳米级粗糙度对1-己基-3-甲基咪唑鎓双（三氟甲基磺酰基）酰亚胺的润滑影响。原子力显微镜首次用于研究润滑接触处的附着力，流体动力滑移和摩擦，其与表面形貌的函数关系。这项研究表明，纳米级粗糙度对沿表面的滑移具有重大影响，并导致具有中等纳米粒子密度的基材上的最大滑移长度。这与在足够小的接触应力下的最小摩擦系数相符，这可能是由于IL膜的抗剪切力较低。但是，在尖锐的尖端施加更高的压力时，摩擦随着纳米颗粒的密度而增加，这表明IL不能减轻由于粗糙度而导致的耗散增加。这项工作的结果指出了表面拓扑对摩擦的复杂影响。这项研究可以帮助设计ILs和纳米图案化的底物，用于摩擦学应用以及纳米和微流体技术。这项工作的结果指出了表面拓扑对摩擦的复杂影响。这项研究可以帮助设计ILs和纳米图案化的底物，用于摩擦学应用以及纳米和微流体技术。这项工作的结果指出了表面拓扑对摩擦的复杂影响。这项研究可以帮助设计ILs和纳米图案化的底物，用于摩擦学应用以及纳米和微流体技术。