We have investigated the relationship between the chemical structure of perfluoropolyether (PFPE) lubricants and their physical and tribological properties on both hydrogenated (CHx) and nitrogenated (CNx) amorphous carbon surfaces. Our work has focused on ultrathin lubricant films in the thickness range of 0∼40 Å that exist in the boundary or molecular lubrication regime. Solution-phase adsorption measurements performed using a quartz crystal microbalance suggest that after initial adsorption, the molecules reorganize on the surface, with the lubricant end group preferentially orienting itself toward the surface. This produces a first monolayer that has unique tribological properties and a strong resistance to displacement. Atomic force microscopy (AFM) friction and adhesive force measurements show a semi quantitative correlation between zero normal load friction and surface energy; however, a strong correlation between adhesive forces and surface energy, which would be expected based on adhesion theory, is not observed. We suggest that this is due to kinetic constraints imposed on the lubricant due to the molecular-scale confinement that it experiences as a thin film. Combined AFM and quartz oscillator measurements extend the velocity of our AFM measurements, providing a velocity range of 10−7 to 1.0 m/s. The data exhibit low friction at velocities below 5 × 10−6 m/s, an increase to a plateau at velocities from 5 × 10−6 to 5 × 10 −4 m/s, and a decrease at velocities above 2 × 10 −2 m/s. The adhesive forces are independent of velocity below 5 × 10−2 m/s and decrease dramatically at higher velocities. We interpret these results in terms of a frictional that is dominated by adhesive forces and interaction thermodynamics. Chemical modification of ZDOL through the addition of a series of hydrocarbon end groups shows that many technologically important properties such as substrate affinity, lubricant volatility, surface energy, and friction coefficients vary systematically with end group structure. A ZDOL derivative that contains reactive vinyl end groups exhibits extremely unique characteristics, forming a crosslinked network on the CNx surface that leads to distinct material properties such as solidification, an exceptionally low surface energy, and a high resistance to displacement.
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机译：我们研究了全氟聚醚（PFPE）润滑剂的化学结构与其在氢化（CHx）和氮化（CNx）非晶碳表面上的物理和摩擦学性能之间的关系。我们的工作重点是在边界润滑或分子润滑方式中存在的厚度范围为0至40的超薄润滑膜。使用石英晶体微量天平进行的溶液相吸附测量表明，初始吸附后，分子在表面重新组织，而润滑剂端基则优先使自身朝向表面。这产生了具有独特的摩擦学特性和抗位移的第一单层。原子力显微镜（AFM）的摩擦力和粘附力测量显示零法向载荷摩擦力与表面能之间的半定量相关性。然而，没有观察到粘附力和表面能之间的强相关性，这是基于粘附理论所预期的。我们认为这是由于润滑剂受到的动力约束所致，因为润滑剂受到薄膜的分子尺度限制。原子力显微镜和石英振荡器的组合测量扩展了原子力显微镜测量的速度，速度范围为10 -7 至1.0 m / s。数据在低于5×10 -6 m / s的速度下表现出低摩擦，在从5×10 -6 到5×10 -4 m / s，并且在高于2×10 -2 m / s的速度下降。粘着力与低于5×10 -2 m / s的速度无关，并且在较高速度下会显着降低。我们以摩擦力来解释这些结果，该摩擦力由粘附力和相互作用热力学决定。通过添加一系列烃端基对ZDOL进行化学修饰表明，许多技术上重要的特性（例如底物亲和力，润滑剂挥发性，表面能和摩擦系数）会随着端基结构的变化而系统地变化。含有反应性乙烯基端基的ZDOL衍生物表现出极其独特的特性，在CNx表面上形成交联网络，从而导致独特的材料性能，例如固化，异常低的表面能和高抗位移性。
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