采用绿色环保的水基润滑剂代替易造成环境污染的油基润滑剂, 是实现绿色摩擦学的有效方法之一。然而, 水基润滑剂普遍存在黏度低、易腐蚀、润滑效果差等问题。该文通过合理的分子结构设计, 将聚合物链式增黏结构与质子型离子液体润滑结构相结合, 制备了具有一定抗腐蚀性能、优异增黏和润滑性能的质子型聚离子液体(PPILs)水基润滑添加剂PPD-N。借助SRV-V微动摩擦磨损试验机和全自动真彩共聚焦显微镜表征了不同温度条件下PPD-N的减摩抗磨性能; 采用扫描电子显微镜(SEM)考察了磨斑的表面微观形貌; 通过光干涉法研究了PPD-N在弹性流体动力润滑状态(EHL)下的润滑性能; 利用X射线光电子能谱(XPS)和飞行时间二次离子质谱(ToF-SIMS)对添加剂的润滑机理进行了研究。结果表明：PPD-N不仅能显著提高水基润滑液的黏度, 还能有效抑制铸铁在水中的腐蚀。与商用增黏剂Koreox W55000相比, 含有6%质量分数PPD-N的水基润滑液的摩擦系数和磨损体积可分别降低约75%和60%。EHL测试结果表明PPD-N水溶液在界面处的薄膜厚度随着滚动速度的增加而增大, 接触区域中心膜厚和润滑剂出口处的最小膜厚均显著高于去离子水。在边界润滑状态下, PPD-N能在摩擦界面处形成吸附膜和摩擦化学反应膜, 两者协同作用, 显著提高了水基润滑液的摩擦学性能。PPD-N不含磷、硫和卤素, 合成简单, 绿色环保, 有望作为难燃液压液和水基全合成金属加工液的增黏、润滑添加剂使用。
Objective: Water-based lubrication has gained significant attention in tribology due to its availability, eco-friendliness, non-flammability, high thermal conductivity, and excellent cleaning properties. Replacing oil-based lubricants, which pose environmental risks, is an effective way toward achieving green tribology. However, water-based lubricants typically face challenges such as low viscosity, susceptibility to corrosion, and inferior lubrication performance. Water-soluble poly(ionic liquid)s, which combine the benefits of polymers and ionic liquids, offer potential as multifunctional water-based lubricant additives to enhance the physicochemical and tribological properties of water-based lubricants. Methods: Through rational molecular structure design, we developed protic poly(ionic liquids) (PPILs) water-based lubricating additives, PPD-N, by combining a polymer chain visco-enhancing structure with a proton-type ionic liquids lubricating structure. PPD-N demonstrates excellent viscosity enhancement, corrosion resistance, and lubricating properties. Kinematic and dynamic viscosities of different water-based lubricating fluids were investigated at 25 ℃ and 40 ℃ using a Pinkevitch Viscometer and a rotational rheometer, with the commercial viscosity builder, Koreox W55000, serving as the control. Following the national standard GB/T 6144—2010, we evaluated corrosion inhibition performance on first-grade gray cast iron using immersion corrosion tests, comparing deionized water, 6% PPD-N, and Koreox W55000 aqueous solution. The friction reduction performance of PPD-N additives was assessed using the SRV-V tester, while its anti-wear properties were characterized using a fully automated real-color confocal microscope. Elastohydrodynamic lubrication properties of PPD-N were investigated by optical interferometry. The surface micromorphology of wear patches was observed using scanning electron microscopy. We also investigated the lubrication mechanisms of the additives using X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). Results: The results of 1H NMR, FT-IR, GPC and TGA tests confirmed the successful synthesis of PPD-N, which demonstrated excellent thermal stability with 5% and 10% thermal decomposition temperatures of 249.7 ℃ and 268.9 ℃, respectively. Adding PPD-N can significantly improve the viscosity of water-based lubricants, with viscosity increasing proportionally to the PPIL additive content. PPD-N also effectively reduced the corrosion of cast iron sheets caused by water-based lubricants, outperforming commercial water-based viscosity builders at equivalent concentrations. At a 6% concentration, the PPD-N aqueous solution achieved a coefficient of friction and wear volume of 0.106 and 22.89×10-5 mm3, respectively, a reduction of about 66% and 85% compared to water's coefficient of friction (0.314) and wear volume (148.20×10-5 m3). Elastohydrodynamic lubrication tests revealed that the PPD-N-containing aqueous solution increased the film thickness at the friction interface with rising velocity. Both the central film thickness and minimum film thickness at the lubricant outlet were significantly higher than those of deionized water. Based on XPS and ToF-SIMS analyses, the lubrication mechanism of PPD-N can be attributed to the formation of tribochemical reaction films and adsorption films at the friction interface. These films effectively prevent direct contact between friction surfaces, endowing the water-based lubricant with superior tribological performance. Conclusions: Compared to the commercial viscosity builder, Koreox W55000, PPD-N additives demonstrate superior lubricity and anti-wear properties. They significantly enhance the viscosity of water-based lubricants and effectively inhibit cast iron corrosion in water. Free of phosphorus, sulfur, and halogens, PPD-N is simple to synthesize, environmentally friendly, and has great potential as a viscosity-building lubricant additive for non-flammable hydraulic fluids and fully synthetic water-based metalworking fluids.
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