Peculiar Effect\nof Water on Tribological Properties\nof Natural Deep Eutectic Solvent

Deep eutectic solvents (DESs) have emerged as promising\ngreen liquid\nlubricants for solving tribological problems due to their economic\nand excellent physicochemical and lubrication properties. However,\na trace amount of water would affect their structure, physicochemical\nproperties, and tribological properties. The effect of water on the\ntribological properties of DES is still unclear and needs further\ninvestigate. Herein, we carried out a systematic investigation into\nthe chemical structure, rheological properties, and tribological performance\nof DES-water (DES-W) binary systems constructed by combining DES with\nvarying contents of water. The results revealed that low levels of\nwater in DES had a minimal impact on its chemical structure but affected\nits fluidity and viscosity. Frictional experiments demonstrated that\nDES-W binary systems displayed a reduced coefficient of friction from\n0.094 to 0.025 compared to pure DESs and manifested outstanding antiwear\nproperties under a high-load condition. This was attributed to the\nformation of hydration layers, adsorption layers, and tribochemical\nfilms at the tribointerface through physicochemical adsorption and\ntribochemical reactions. Our findings not only foster the design and\ndevelopment of green lubricating materials but also expand the engineering\napplications of DESs to solve wear-related mechanical failures in\npractical application.