Low-Viscosity Hydrophobic Deep Eutectic Solvents as Sustainable Lubricants for Ball Screws

As core components of precision transmission systems, ball screw pairs frequently confront the inherent challenge of simultaneously reconciling high load-carrying capacity with low friction. Conventional approaches typically enhance load capacity by increasing lubricant viscosity, however, this induces severe viscous shearing during high-speed operation, resulting in substantial energy dissipation and compromised transmission accuracy due to thermal effects. To address this dilemma, this study synthesized a series of natural hydrophobic deep eutectic solvents (DESs) based on menthol, thymol, and carvacrol, aiming to develop novel lubricants that possess both high load-carrying capacity and low shear characteristics. Experimental results demonstrate that these hydrophobic DESs sustain remarkably low coefficients of friction (COF) and wear rates even under an extremely high contact pressure of 2.98 GPa. Mechanistic investigations reveal that minimized molecular steric hindrance, strong hydroxyl acidity, and specific component ratios are pivotal for the formation of robust physical adsorption films. Furthermore, their unique hydrophobic nature effectively overcomes the inherent water sensitivity of traditional DESs. In bench tests simulating actual operating conditions, the developed lubricants significantly enhanced the motion stability of the ball screw, exhibiting superior high-precision and low-friction performance. In summary, these green, facilely prepared, and property-tunable lubricants present an ideal lubrication solution for precision transmission components and provide significant theoretical insights for the advancement of sustainable lubrication technologies.