Elastohydrodynamic Lubrication Mechanisms of Aqueous Polyethylene Glycols

Abstract Water-soluble polyalkylene glycols have become a growing subject of research to achieve liquid superlubricity in elastohydrodynamically lubricated contacts. While the influence of various factors, including water content and viscosity, has been extensively studied, the underlying mechanisms responsible for liquid superlubricity under elastohydrodynamic lubrication remain poorly understood. In this study, aqueous polyethylene glycols of varying average chain length with the same viscosity but different water content or average chain length distribution are examined in relation to elastohydrodynamic friction and film thickness. The results indicate, that under fluid film lubrication, the low pressure–viscosity coefficient is the primary factor leading to liquid superlubricity. No running-in period is required, allowing for stable and persistent ultra-low friction level immediately. Additionally, at a constant water content, an optimum average chain length distribution was identified, resulting in reduced friction while the film thickness remained largely unaffected. This enables the targeted design of aqueous lubricants based on polyethylene glycol. Graphical abstract