Synthesis of Novel Deep Eutectic Solvents for Ultralow Wear Performance at the Steel/Steel Interface under High Pressure

Deep eutectic solvents (DESs) have attracted widespread attention in the lubrication field, yet achieving effective steel–steel wear resistance remains challenging. This study develops a thiodisuccinic acid/trioctylphosphine oxide-based deep eutectic solvent (DES) with tunable hydrogen-bonding networks for steel/steel interface lubrication. At a 1:4 molar ratio, the DES achieves a friction coefficient of 0.05 and an ultralow wear rate (4.44 × 10 –9 mm 3 ·N –1 ·m –1 ) under 1.08 GPa contact pressure. Remarkably, the DES exhibits sustained lubricity, maintaining a wear rate of 1.13 × 10 –8 mm 3 ·N –1 ·m –1 after 110,000 cycles. The key lubrication mechanism is attributed to the multihydrogen-bonding network that enhances lubricant film load-carrying capacity and mixed lubrication. This work presents a novel approach for engineering high-performance DESs with exceptional antiwear properties for steel surfaces.