Macroscale and durable near-zero wear performance on steel surfaces achieved by natural ternary deep eutectic solvents

The development of environmentally friendly and cost-effective lubricating materials to reduce friction and wear at the macroscale is crucial for reducing fuel consumption and exhaust emissions, thereby enhancing sustainability. Deep eutectic solvents (DESs) have emerged as viable alternatives to traditional lubricants due to their ease of preparation, affordability, reproducibility, and superior tribological properties. Herein, a series of natural ternary DESs (TDESs) are successfully developed by blending eco-friendly and economical D-sorbitol and ethanolamine with quaternary ammonium salts through hydrogen bond interactions that may be regarded as a new and green liquid lubricating system. The synthesized TDESs exhibit exceptional thermal stability, rheological properties, corrosion resistance, and wettability towards metallic substrates. Moreover, the experimental results combined with molecular dynamics simulations indicate that the TDESs can form a robust protective lubricating film on steel surfaces through polar adsorption and tribochemical reactions. Consequently, the synthesized TDESs demonstrate a low friction coefficient (∼0.1) and ultra-low wear rate (as low as 7.8 × 10−10 mm3 N−1 m−1), exhibiting a near-zero wear behavior on steel surfaces under high load (100 N) and multi-environment scenarios. This research not only highlights the potential applications of DESs in tribology but also provides guidance for the future generation of green and high-performance liquid lubricating materials.