The presence or absence of unsaturation in the carbon chain of carboxylic acids was examined on the friction response of boundary films according to normal force. Friction laws were established as a function of the normal force at the nanoscale with a molecular tribometer derived from a surface force apparatus. While the shear plane is mainly composed of methyl groups in all the cases investigated, the molecular organization differs within the shear plane, as suggested by the simultaneous film thickness evolution. This gave rise to dissipation modes within the interface, resulting in a wide range of shear stress levels and dependence with contact pressure. The friction laws were discussed, highlighting the combined role of nanometric surface roughness and molecule unsaturation.

Graphic Abstract

Friction laws for stearic acid ( ), elaidic acid ( ), and oleic acid ( ) boundary layers and schematic diagrams of the corresponding sheared interfaces

中文翻译：

---

饱和/不饱和脂肪酸层的摩擦定律

根据法向力，在边界膜的摩擦响应上检查了羧酸的碳链中是否存在不饱和键。利用源自表面力装置的分子摩擦计，建立了摩擦定律作为纳米级法向力的函数。在所有研究的案例中，尽管剪切平面主要由甲基组成，但分子膜的组织在剪切平面内却有所不同，这是由同时发生的膜厚演变所暗示的。这引起了界面内的耗散模式，从而导致了较大范围的剪切应力水平以及对接触压力的依赖性。讨论了摩擦定律，强调了纳米表面粗糙度和分子不饱和度的组合作用。

图形摘要

硬脂酸（），依地酸（）和油酸（）边界层的摩擦规律及相应剪切界面的示意图。