Superlubricity and Corrosion Inhibition Properties of Solvate Ionic Liquids in Hybrid Carbon Fiber Reinforced Plastic–Steel Interfaces

This study demonstrates the dual functionality of solvate ionic liquids (SILs) comprising lithium bis(trifluoromethanesulfonyl)imide ([LiTFSI]) coordinated with triethylene glycol dimethyl ether ([Li(G3)][TFSI]) or tetraethylene glycol dimethyl ether ([Li(G4)][TFSI]) as both high‐performance lubricants and effective corrosion inhibitors at polymer–steel interfaces. Tribological testing of polyamide 6 (PA6), polyphenylene sulfide (PPS), and their carbon–fiber (CF) composites revealed that SIL lubrication reduced the coefficient of friction by ∼60% compared to dry sliding, reaching steady‐state values as low as 0.04–0.05 for PPS lubricated with [Li(G4)][TFSI]. Dry PPS/CF composites exhibited elevated CoF up to ∼0.60, underscoring the benefit of SIL retention and tribofilm formation. SEM examination of stainless‐steel surfaces following 24‐h immersion confirmed that both [Li(G3)][TFSI] and [Li(G4)][TFSI] were noncorrosive, in contrast to severe pitting observed in 1 M HCl. Corrosion weight‐loss measurements in 1 M HCl further demonstrated clear inhibition behavior, with only 100 ppm of [Li(G3)][TFSI] (∼68.5 μL/L) reducing corrosion‐product weight loss by 63% compared to 54% for 100 ppm [Li(G4)][TFSI] (∼71.4 μL/L). Complementary electroimpedance spectroscopy analysis revealed distinct interfacial responses for the two SILs, [Li(G3)][TFSI] ( R ct = 366 Ω, interface inhibition effect of ∼40%) and [Li(G4)][TFSI] ( R ct = 308 Ω, interface inhibition effect of ∼28%), indicating a more pronounced modification of the steel–electrolyte interface.