Amine- and hydroxyl-functionalized copolymers as lubricant additives on Si-doped DLC: A comparative experimental and computational study of their tribological performance

Diamond-like carbon (DLC) coatings combined with functionalized copolymers are promising environmentally friendly lubrication systems and alternatives to metal containing additives. This study examines silicon-doped DLC (Si-DLC) lubricated with block copolymers bearing amine (DMAEMA) or hydroxyl (HEMA) groups. Friction and wear tests over 20–80 °C and under different loads show that both copolymers provide lower friction relative to nonfunctionalized PLMA, but only DMAEMA sustains low friction and low wear under 100 N boundary lubrication. To clarify the mechanism, a distribution-based ab initio adsorption analysis was carried out on an amorphous Si-DLC model using a screening procedure across multiple surface sites and molecular orientations. The adsorption energy distributions show that DMAEMA frequently forms stable N–Si bonds (often ≤ − 2.0 eV) and dual N–Si + O–Si bonds (about − 2.4 eV), whereas HEMA centers near − 1.5 eV for OH–Si bonds, with weaker dual OH–Si + O–Si bonding (about − 2.0 eV). This separation of adsorption energy distributions accounts for the divergence in high load behavior. Together, experiments and modeling underline the role of functional group chemistry in determining tribological performances on Si-DLC, and adsorption energy distributions, and guide additive selection for Si DLC in electric and hybrid drivetrains.