Tribological performance of aqueous copolymers solutions in metallic contact
Tribology performances (friction and anti-wear) of aqueous symmetrical tri-block normal and reverse copolymer solutions have been investigated. The ball-on-disk experiment was carried out to measure the coefficient of friction of solutions used at ~25°C and ~50°C. The interaction of alkyl phosphate ester, an anionic surfactant, and the aqueous copolymer solutions was also investigated. When solution was supplied at ~50°C, high friction and severe wear were found indicated that the solutions were not able to protect the surface. The friction and the anti-wear was found to improve when solution used at ~25°C. However, adding alkyl phosphate ester as extreme pressure additive into aqueous solutions produced a stronger adsorbed lubricant film protecting the surface. Low COFs were obtained from solutions below and above the cloud point. For the wear volume, the presence of phosphate ester produced comparable wear with the solution without added alkyl phosphate ester. The stainless steel was found less reactive to the alkyl phosphate ester hence the wear not much reduced. The possible lubrication mechanism is discussed by analysing the worn tracks using Scanning Electron Microscope (SEM), Atomic Force Microscope (AFM) and the water contact angle measurements.