An Ecofriendly Design for Superhydrophilic Natural Deep Eutectic Solvent Lubricants and Their Excellent Interfacial Behavior

The need for low-viscosity and sustainable lubricants has always been urgent for the application of complex materials and the improvement of machining accuracy requirements. As a kind of lubricating material with the characteristics of easy preparation and designable structure, deep eutectic solvent (DES) shows excellent performance controllability and good application potential. Herein, a series of phosphate menthol DESs (P-DL) were designed and prepared as high-performance lubricants. The results of their physicochemical properties show that the synthesized DESs exhibit low viscosity and superhydrophilicity, providing more efficient adsorption and interfacial self-assembly behavior. Additionally, enhanced corrosion resistance and thermal stability are conducive to their chemical stability during shearing. In terms of tribological properties, P-DL exhibits optimal friction-reducing and antiwear properties, along with load-bearing performance. More importantly, excellent lubrication stability can be obtained even under more stringent and diverse test conditions, indicating the universality and great engineering application potential of these materials as sustainable lubricants. More hydrogen bond donors, longer alkyl chains, and suitable branched structures have a positive effect concerning the comprehensive function. Besides, the synergistic effect of superhydrophilicity, polar adsorption, and tribochemical reaction is the key factor for the robust lubrication performance. In addition, easy preparation, high-performance, and sustainability all provide great application potential for these lubricants. Meanwhile, this chemically designed lubricant optimization strategy with adjustable performance also provides theoretical guidance for the development and enrichment of sustainable lubrication technology.