Effect of TiO2 nanoparticles on wettability and tribological performance of aqueous suspension

Aqueous suspensions containing different concentration of nano-TiO2 (50 nm) are prepared, in which sodium polyacrylate (PAAS) as the dispersant is used. Their wettability and tribological properties are discussed with Dataphysics OCA50 contact angle measurement device and the MRS-10A four-ball tester, respectively. The rubbed surfaces after friction tests are also analyzed by scanning electron microscope (SEM) equipped with Energy Dispersive Spectrometer (EDS). Wetting results show that the wettability of aqueous suspension is sharply deteriorated with the addition of PAAS, possibly caused by adsorption of PAAS on the substrate alters the characterization of the substrate, which promote the substrate change from homogeneity to heterogeneity, and eventually the wetting state transits from Wenzel to Cassie. And when the nano-TiO2 is further added to the aqueous suspension, the wettability is slightly better, which is mostly due to adsorbed sodium polyacrylate desorb from substrate surface and return to the body phase. In another aspect, four-ball experimental results reveal that the nano-TiO2 as the additive exhibits good anti-wear and friction reduction properties as well as load-carrying capacity. SEM analysis indicates that nano-TiO2 is deposit on the rubbed surface and so prevents direct contact of tribo-pairs.