Department of Chemistry, Faculty of Natural Sciences, Imperial College London , SW7 2AZ London, U.K.
School of Chemistry, Faculty of Exact Sciences and the Sackler Center for Computational Molecular and Materials Science, Tel Aviv University , Tel Aviv 6997801, Israel.
ACS Nano. 2017 Jul 25;11(7):6825-6831. doi: 10.1021/acsnano.7b01835. Epub 2017 Jun 26.
To a greater or lesser extent, most room-temperature ionic liquids (RTILs) absorb water from humid air. Penetration of water into the lubricating nanoscale film may affect its equilibrium structure and dynamic properties and thus influence the ability of RTILs as lubricants to reduce friction between solid surfaces. Here we investigate the impact of hydration on lubrication using nonequilibrium molecular dynamics simulations. Water adsorption changes both the ionic liquid molecules' orientation and the slip conditions at the solid-liquid interfaces, resulting in a reduced resistance against squeezing-out of the lubricant by an external load. For the same normal load, the film becomes thinner when water is present. We show that even small amounts of water can screen the electrostatic interactions between the ions, making RTILs more "fluid" and compressible and hence less resistant to external stress. The impact that screening has on friction involves several aspects that are systematically analyzed in this paper.
在不同程度上，大多数室温离子液体（RTILs）都会从潮湿空气中吸收水分。水渗透到润滑的纳米薄膜中可能会影响其平衡结构和动态特性，从而影响 RTILs 作为润滑剂减少固体表面之间摩擦的能力。在这里，我们使用非平衡分子动力学模拟研究了水合作用对润滑的影响。水的吸附改变了离子液体分子的取向和固液界面的滑移条件，从而降低了润滑剂在外载荷下挤出的阻力。在相同的法向载荷下，当存在水时，薄膜会变薄。我们表明，即使少量的水也可以屏蔽离子之间的静电相互作用，使 RTILs 更“流动”和可压缩，因此对外力的抵抗力更小。屏蔽对摩擦的影响涉及几个方面，本文对这些方面进行了系统分析。
