Molecular Geometry Governs Interlayer Orientation: Confined Carbonization of Deep Eutectic Solvent-Intercalated Hydrotalcite for Universal Lubrication via Hybrid Tribofilm

Abstract

Lubrication additives that combine high efficiency at low concentrations with broad universality are urgently needed for breaking through the bottleneck of current lubricants. Herein, two novel green deep eutectic solvents are designed using tartaric acid (TA), malic acid (MA), and L-carnitine and inserted into layered double hydroxide (LDH) gallery to fabricate four intercalated LDH composites. The intercalation successfully exfoliates pristine LDH material, and ultra-thin flexible sheets can be obtained with the controllable interlayer spacing, based on guest molecular geometries and interlayer configurations. The tribological performance reveal that molecular intercalation expands the interlayer spacing and improves interlayer shear, while the confined gallery space together with hydrogen bonding interactions enables in situ carbonization of guest molecules, forming a carbonaceous or nitrogen-doped carbon film. Moreover, LDH itself undergoes tribo-chemical reactions to transform into inorganic nanocrystals (ZnO, ZnAl₂O₄), which together with the carbon film, constitute a robust hybrid tribofilm. Eventually, TADES-LDH (rigid planar geometry, flat-lying configuration) exhibits excellent long-term lubrication, anti-wear (decreases by over 90%), and load-bearing properties (500 N), while achieves surprising universality across a wide range of base fluids (PEG, water, ester oil, liquid paraffin). This work offers a new paradigm for designing high-performance, universal lubricant additives toward the sustainable lubrication technology.