Hydrophilicity characterization of Al2O3-coated MoS2 particles by using thin layer wicking and sessile drop method

Abstract

When hydrophobic particles are employed to prepare self-lubricating electroless composite coatings, they usually require surface modification to improve their wettability. The study focuses on the resultant change in wettability of the MoS2 particles with an inorganic coating. Al2O3-coated MoS2 particles were prepared by using a heterogeneous nucleation process. Then, particle surface morphology and structure were examined by using SEM, EDS and XRD. Contact angle measurements were conducted by using a thin layer wicking technique and a sessile drop method in order to determine the surface free energy components of the bare and the coated MoS2 particles. Our results showed the MoS2 particles were successfully coated with an Al2O3 layer, which is an amorphous structure. The decreased water contact angle indicates an enhanced hydrophilicity for the coated particles. This decrease depends more strongly on a significant decrease of a new parameter ratio, γ+/γ−, than on a slight increase in total surface free energy. The surface energy component of the bare MoS2 is very consistent with that of Talc, and that of the Al2O3-coated one is very similar to that of alumina, apart from the base component.