Friction of Ionic Liquid-Glycol Ether Mixtures at Titanium Interfaces: Negative Load Dependence
Friction of Ionic Liquid-Glycol Ether Mixtures at Titanium Interfaces: Negative Load Dependence
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离子液体与乙二醇醚混合物在钛界面处的摩擦：负负载依赖性
DOI：
10.1002/admi.201800263
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发表时间：
2018-07-23
影响因子：
5.4
通讯作者：
Shah, Faiz Ullah
中科院分区：
文献类型：
--
作者：
An, Rong;Zhou, Guobing;Shah, Faiz Ullah
原子力显微镜实验和非平衡分子动力学（NEMD）模拟表明，离子液体-乙二醇醚混合物的摩擦载荷负相关，即摩擦随法向载荷的增加而减小。NEMD模拟揭示了所研究的离子液体（IL）的结构取向：随着法向负载的增加，离子液体的阳离子烷基链改变取向，优先平行于尖端扫描路径。平面定向的IL结构，类似于盛开的荷叶，产生了新的滑动界面，减少了摩擦。采用裂隙-孔模型模拟叶尖接近过程，进一步进行分子动力学模拟，以确定叶尖接近过程的动力学性质。观察到在较小的狭缝孔中，il的扩散速度更快。在更狭窄的狭缝孔隙中，il的扩散速度更快，有利于il的结构重定向。由此产生的新的滑动面负责观察较小的摩擦在更高的载荷，也被称为负摩擦载荷依赖。这些发现为il在界面润滑中的作用提供了一个基本的解释。它们有助于理解约束下的液体流动特性，对开发更好的纳米流体器件具有指导意义。
The atomic force microscopy experiments and nonequilibrium molecular dynamics (NEMD) simulations demonstrate a negative friction-load dependence to ionic liquid-glycol ether mixtures, that is, the friction decreases as the normal load increases. NEMD simulations reveal a structural reorientation of the studied ionic liquid (IL): as the normal load increases, the cation alkyl chains of ILs change the orientation to preferentially parallel to the tip scanning path. The flat-oriented IL structures, similar to the blooming lotus leaf, produce a new sliding interface and reduce the friction. A further molecular dynamics simulation is carried out by adopting slit-pore models to mimic the tip approaching process to confirm the dynamics of ILs. A faster diffusion of ILs in the smaller slit pore is observed. The faster diffusion of ILs in the more confined slit pore facilitates the structural reorientation of ILs. The resulted new sliding surface is responsible for the observed smaller friction at higher loads, also known as the negative friction-load dependence. These findings provide a fundamental explanation to the role of ILs in interfacial lubrications. They help to understand liquid flow properties under confinement, with implications for the development of better nanofluidic devices.