Effects of Nanoscale Roughness on the Lubricious Behavior of an Ionic Liquid
Effects of Nanoscale Roughness on the Lubricious Behavior of an Ionic Liquid
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DOI：
10.1002/admi.202000314
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发表时间：
2020-06
影响因子：
5.4
通讯作者：
P. Nalam;Alexis Sheehan;Mengwei Han;R. Espinosa‐Marzal
中科院分区：
文献类型：
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作者：
P. Nalam;Alexis Sheehan;Mengwei Han;R. Espinosa‐Marzal
虽然许多机理研究都集中在理想光滑表面上离子液体的润滑性能，但对离子液体润滑与纳米级粗糙度接触的机理却知之甚少。在这里，我们制备了纳米颗粒密度可控的基片，以考察纳米粗糙度对1-己基-3-甲基咪唑双(三氟甲基磺酰亚胺)亚胺润滑的影响。原子力显微镜首次被用来研究润滑接触处的粘附力、流体动力滑移和摩擦作为表面形貌的函数。研究表明，纳米级粗糙度对表面滑移有显著影响，在纳米颗粒密度适中的衬底上，滑移长度最大。这与足够小的接触应力下的最小摩擦系数相吻合，这可能是由于IL膜的剪切阻力较低。然而，在尖端尖端施加的较高压力下，摩擦力随着纳米颗粒密度的增加而增加，这表明IL不能缓解由于粗糙度而增加的耗散。这项工作的结果指向了曲面拓扑对摩擦的复杂影响。这项研究可以帮助设计ILS和纳米涂层衬底，用于摩擦学应用和纳米和微流体。
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.