Polyethylene Glycol Monolaurate Lubrication Triggers Liquid Superlubricity on Diamond-like Carbon Film

Achieving the ultralow coefficient of friction (COF) is the goal pursued by the industrial field. In this work, the macroscopic superlubricity with a COF of 0.003 on the DLC film was achieved at an approximate temperature of 45–100 °C when it slid against the steel ball with the lubrication of polyethylene glycol monolaurate (PEGM). The superlubricity state was achieved in a mixed lubrication regime, mainly containing boundary lubrication and thin film lubrication. The friction action under high temperature facilitated the chemisorption of PEGM molecules on the friction pair to form the tribochemical films, providing a low shear strength under boundary lubrication. Meanwhile, the PEGM molecules could form an ordered layer and a liquid layer on the tribochemical films due to the strong polarity of PEGM molecules, which attained the thin film lubrication to reduce friction. Moreover, the friction promoted the in situ generation of carbonaceous sheets in the contact region, providing low shear strength and reducing COF under boundary lubrication. This finding provides insight into the superlubricity mechanism of DLC film and expands its engineering application in superlubricity technology.