Grafting and characterization of dodecylphosphonic acid on copper: Macro-tribological behavior and surface properties

Abstract

Thin film of n-dodecylphosphonic acid (DDPA) was prepared on a copper oxide substrate via a molecular self-assembly process. The composition, structure, organization, surface energy, morphology, and electrochemical behavior of the DDPA film were characterized by means of X-ray photoelectron spectroscopic analysis (XPS), polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS), contact angle measurement (CAM), microscopic observations, and electrochemistry. The friction behavior of the DDPA film adsorbed on copper oxide substrate sliding against a Si3N4 ball was examined on a linear reciprocating tribological tester. Worn surfaces of the DDPA film were observed with a scanning electron microscope. All properties of the DDPA film were compared and discussed in terms of sonication effects just after surface functionalization. The presence and organization of alkyl phosphonate molecule on Cu were confirmed by XPS, PM-IRRAS and CAM analyses. PM-IRRAS data gave some indication of tridentate bonding between phosphonic groups and oxidized Cu surface. Electrochemical studies showed strong anti-corrosion behavior. Excellent tribological behavior was observed for DDPA film before sonication (DDPA/Cu BS) under contact pressure of 133MPa and low sliding speed of 1mm·s−1 conditions. In the case of DDPA/Cu BS surface, very low friction coefficient value (μ≈0.12) and increase in antiwear life (100 times higher) were observed, compared to a DDPA film after sonication (DDPA/Cu AS) and a bare Cu substrate.