In Situ-Formed Ultralow Wear Tribofilms Induced by Poly(Acrylic Acid)-co-MXene-Modified Polymer-Like Carbon Films

Herein, two types of tribocouple pairs based on polymer-like carbon (PLC) films are designed through the in situ-formed MXene coating. The in situ-formed MXene coatings are synthesized via the in situ organic–inorganic chemical composite technique-induced anionic polymers with different molecular weights (≈450 000 and ≈4 000 000, respectively). Next, the tribotesting condition is controlled in the ambient environment under different loads by bare and PLC-coated bearing steel balls as counterbodies. During the whole sliding process, a lubricity state (friction coefficient is about 0.21 and wear rate is about 1.5 × 10⁻⁶ mm³ N⁻¹ m⁻¹) is realized on the self-mated PLC system. Meanwhile, the contact surfaces are covered by graphitic 2D Ti₃C₂. Compared with the high-molecular-weight modifier system, most poly(acrylic acid)-co-MXenes grafted by the low-molecular-weight poly(acrylic acid) form far more sp ²-C phases. Moreover, active groups are potentially involved in forming a tribofilm, which enhances the overall lubricity of MXenes during sliding. This verifies the key to achieving low friction and ultralow wear based on the formation of the nanostructured sliding interface upon MXenes and provides an expanded application of solid lubricants.