Friction-triggered self-reactive deep eutectic solvents for tunable lubrication under an ultra-heavy load through in situ formation of an ultra-thick multi-gradient tribofilm

Abstract

To ensure the reliable operation of mechanical systems under increasingly severe conditions, developing intelligent lubricants with harsh condition self-adaptability, tunable interface behavior and enduring lubrication is a promising solution. Herein, we propose friction-triggered self-reactive deep eutectic solvents (DESs) that actively construct an adaptive tribo-film via chemical reactions between the hydrogen-bond acceptor and donor, without external catalysts or sacrificial tribo-pair materials. Under an ultra-heavy load (3090 N, Hertzian contact stress of 6 GPa), the system achieves an ultra-low friction coefficient of 0.05 and a minimal wear scar diameter of 0.7 mm, surpassing the highest load-bearing capacity of reported DES lubricants (1568 N). The outstanding properties originate from an ultra-thick (∼565 nm) multi-gradient tribofilm, consisting of a dynamic amorphous top layer for absorbing frictional energy, dissipating contact stress and avoiding adhesive wear; an intermediate MoS₂ nanocrystal layer for providing load support and low shear; and a metal-oxide anchoring layer for anchoring the substrate and stabilizing the tribofilm. This multi-gradient architecture confines shear deformation to the interface between the top amorphous layer and the intermediate layer, effectively providing low shear resistance, buffering high contact stress, and preventing damage to the underlying substrate. This work provides a new strategy for designing smart lubricants with harsh-condition adaptability and on-demand friction control, offering both mechanistic insights and a practical pathway toward durable interfacial protection under extreme operating conditions.