Green Ionic Polymer Additives for Multifunctional Integration in Water‐Based Lubrication Systems: Lubricity, Anti‐Corrosion and Viscosity‐Enhancing Properties

Environmentally benign water‐based lubricants are attracting increasing attention as alternatives to conventional oil‐based lubricants that may cause environmental pollution. Herein, three protic poly(ionic liquid)s (PPILs) are synthesized by combining a copolymeric cation with carboxylate anions of different alkyl chain lengths. The PPILs are employed as additives in aqueous lubricants, and their viscosity‐enhancing capability and tribological performance are systematically evaluated. Quartz crystal microbalance (QCM), electrical contact resistance (ECR), X‐ray photoelectron spectroscopy (XPS), and time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) are used to elucidate the lubrication mechanism. The results demonstrate that PPILs significantly improve the viscosity, corrosion resistance, and tribological properties of water‐based lubricants. Notably, the kinematic viscosity of a 6% PPD‐Oa aqueous solution increases by two orders of magnitude compared with deionized water, while the corresponding wear volume and coefficient of friction are reduced by approximately 77% and 70%, respectively. Mechanistic investigations indicate that interfacial adsorption and friction‐induced chemical processes jointly generate a protective layer at the sliding interface, thereby imparting excellent lubricity and load‐bearing capability to the lubricant. Moreover, the three sulfur‐free and halogen‐free PPILs represent environmentally benign additives with strong potential for application in metalworking fluids and hydraulic systems.