Micro-scratch behaviour of adsorbed film formed by aqueous copolymer lubricants with phosphate ester additive on Ti-coated surface
The adsorption behavior and the adhesion strength of lubricant films formed by polypropylene oxidepolyethylene oxide-polypropylene oxide (PPO-PEO-PPO) with phosphate ester additive on Ti-coated surface and the influence of molecular architecture and phosphate ester additive was studied. The thickness of the adsorbed PPO-PEO-PPO with phosphate ester lubricant films on Ti surfaces was measured by ellipsometry. The adhesion strength of the copolymer and the copolymer with phosphate ester lubricants was studied by the micro-scratch tests; the scratch tracks on the surfaces were observed by atomic force microscopy and scanning electronic microscopy. The copolymer with a higher weight percentage of PPO not only formed a thicker film but also showed stronger adhesion and better lubrication performance. The added phosphate ester increased the film thickness and improved the tribological behaviour. The finding reveals that the adsorbed film thickness which depends on the PPO chain length and the presence of phosphate ester has a considerable effect on the scratch behavior.