Adsorbed film structure and tribological performance of aqueous copolymer lubricants with phosphate ester additive on Ti coated surface
The adsorption of aqueous tri-block reverse copolymer polypropylene oxide-polyethylene oxide-polypropylene oxide, PPO-PEO-PPO with phosphate ester on Ti coated surfaces have been studied using a neutron reflectometer (NR). It is found that the adsorbed film consists of two layers. The hydrophobic PPO block forms the inner layer and acts as the anchor of the adsorbed film. Copolymer with higher weight percentage of PPO forms a thicker PPO layer. Phosphate ester affects the adsorbed film structure of PPO-PEO-PPO copolymer by forming a thicker mixed-layer of PPO and phosphate ester on the Ti surface. The tribological performance of the lubricants has also been studied using a ball-on-disc tribometer. The results show that copolymer molecular structure affects lubrication performance. Tr-block copolymer with a higher weight percentage of PPO shows a better performance. The addition of phosphate ester to tri-block copolymer solution not only significantly decreases the coefficient of friction but also increases anti-wear property. The finding indicates that adsorbed film thickness depends on the size of the PPO block and the presence of phosphate ester, and that adsorbed film thickness correlates with friction.