Deep eutectic solvents (DESs) are acknowledged as a novel class of functional liquid. DESs share similar physical properties with ionic liquids (ILs) and have the potential to be a novel class of lubricants. In this study, two DESs, namely tetrabutylammonium chloride-decanoic acid DES (C4-DES) and methyl tricaprylmethylammonium chloride-decanoic acid DES (C8-DES), were synthesized, and their physico-chemical properties and tribological performances were evaluated. Post-analysis of the rubbing surfaces used multiple techniques to gain insights into the lubrication mechanisms. Results show that the coefficient of friction (COF) and wear were reduced by approximately 29% and 91% for the C4-DES, and 36% and 94% for the C8-DES, compared to an ester base oil. The friction reduction behavior of the DESs is attributed to the monolayer adsorption of the polar group in the decanoic acid (DEAC), whose effectiveness is affected by the component of the ammonium salts in the DESs and the operating temperatures. In addition to the adsorbed film, worn surface analysis revealed that an ultra-thin tribochemical film with a thickness of 3–7 nm was formed on the surfaces lubricated with the C8-DES. The composition of the film was studied, and the lubrication mechanisms of the two DESs were discussed.

低共熔溶剂（DES）被认为是一类新型功能液体。 DES 与离子液体 (IL) 具有相似的物理特性，有潜力成为一类新型润滑剂。本研究合成了两种DES，即四丁基氯化铵-癸酸DES（C4-DES）和甲基三辛基甲基氯化铵-癸酸DES（C8-DES），并评估了它们的物理化学性能和摩擦学性能。摩擦表面的后分析使用多种技术来深入了解润滑机制。结果表明，与酯基础油相比，C4-DES 的摩擦系数 (COF) 和磨损分别降低约 29% 和 91%，C8-DES 分别降低 36% 和 94%。 DES 的减摩行为归因于癸酸 (DEAC) 中极性基团的单层吸附，其有效性受到 DES 中铵盐的成分和工作温度的影响。除了吸附膜外，磨损表面分析表明，在用 C8-DES 润滑的表面上还形成了厚度为 3-7 nm 的超薄摩擦化学膜。研究了薄膜的组成，并讨论了两种 DES 的润滑机制。