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Nanotribology of Ionic Liquids: Transition to Yielding Response in Nanometric Confinement with Metallic Surfaces
Physical Review X ( IF 12.5 ) Pub Date : 2020-03-20 , DOI: 10.1103/physrevx.10.011068
Antoine Lainé , Antoine Niguès , Lydéric Bocquet , Alessandro Siria

Room-temperature ionic liquids (RTILs) are molten salts which exhibit unique physical and chemical properties, commonly harnessed for lubrication and energy applications. The pure ionic nature of RTIL leads to strong electrostatic interactions among the liquid, furthermore exalted in the presence of interfaces and confinement. In this work, we use a tuning-fork-based dynamic surface force tribometer, which allows probing both the rheological and the tribological properties of RTIL films confined between a millimetric sphere and a surface, over a wide range of confinements. When the RTIL is confined between metallic surfaces, we see evidence of an abrupt change of its rheological properties below a threshold confinement. This is reminiscent of a recently reported confinement-induced capillary freezing, here observed with a wide contact area. In parallel, we probe the tribological response of the film under imposed nanometric shear deformation and unveil a yielding behavior of the interfacial solid phase below this threshold confinement. This is characterized by a transition from an elastic to a plastic regime, exhibiting striking similarities with the response of glassy materials. This transition to yielding of the RTIL in metallic confinement leads overall to a reduction in friction and offers a self-healing protection of the surfaces avoiding direct contact, with obvious applications in tribology.

中文翻译:

离子液体的纳米摩擦学:在金属表面的纳米约束下向屈服响应的过渡

室温离子液体(RTIL)是熔融盐,具有独特的物理和化学特性,通常用于润滑和能源应用。RTIL的纯离子性质会导致液体之间发生强烈的静电相互作用,此外,在存在界面和密闭情况下,这种作用会更加明显。在这项工作中,我们使用基于音叉的动态表面力摩擦计,该摩擦计允许在很宽的范围内探测被限制在毫米球和表面之间的RTIL膜的流变和摩擦学特性。当RTIL被限制在金属表面之间时,我们看到其流变特性在阈值限制以下突然改变的证据。这使人联想到最近报道的限制引起的毛细血管冻结,此处观察到了较宽的接触面积。同时,我们在施加的纳米剪切变形下探测了薄膜的摩擦学响应,并揭示了在该阈值限制以下的界面固相的屈服行为。其特征是从弹性状态过渡到塑性状态,与玻璃质材料的响应表现出惊人的相似性。在金属限制下向RTIL屈服的过渡总体上减少了摩擦,并为表面提供了自我修复保护,避免了直接接触,在摩擦学中有明显的应用。与玻璃质材料的反应表现出惊人的相似性。在金属限制下向RTIL屈服的过渡总体上减少了摩擦,并为表面提供了自我修复保护,避免了直接接触,在摩擦学中有明显的应用。与玻璃质材料的反应表现出惊人的相似性。在金属限制下向RTIL屈服的过渡总体上减少了摩擦,并为表面提供了自我修复保护,避免了直接接触,在摩擦学中有明显的应用。
更新日期:2020-03-20
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