Mechanism of Wettability Interface of Emulsion in Hydrodynamic Based on Dichromatic Fluorescence Method

Emulsions are widely used in fields such as rolling and cutting, and the lubrication mechanism of emulsions has been continuously improved. However, there are relatively few research results on emulsions in fluid dynamic pressure lubrication. In order to further investigate the lubrication mechanism of emulsions at the interface of fluid dynamic pressure lubrication, Nile red, fluorescent agent with the concentration of 0.5 mmol/L, was added to the emulsion to label the oil phase, and water-soluble fluorescent probe PEG carboxylated CdSe/ZnS was added to label the aqueous phase, in which the fluorescence excitation at the aqueous phase fluorescent probe was red and the fluorescence at the excitation of the oil phase fluorescent probe was green. The bearing steel blocks were coated with AF and FAS with different degrees of hydrophobicity and oleophobicity to observe the competitive adsorption behaviors of the oil and water phases at different surface interfaces during the movement process. The emulsion after fluorescent labeling treatment was diluted by 10% concentration gradient, and the minimum film thickness in emulsion lubrication at different surface interfaces was measured by optical interferometry, and the competitive migration behavior of the oil and water phases in the contact zone and the surrounding pool of emulsion was observed by dichromatic fluorescence method. The results showed that the diluted emulsion still had a good film-forming ability, and the emulsion film thickness was positively correlated with the size of the coiling and suction speeds, but the size of the film thickness at different speeds would appear cross phenomena. The film-forming ability of the emulsion was different at different surface interfaces, in which the film thickness was highest on the AF surface, second on the Steel surface, and lowest on the FAS surface. Observing the change of the oil pool during the motion, the shape of the emulsion pool would change with the change of speed, and part of the emulsion would pass directly through the contact area along the direction of motion of the slider/glass disk, while the other part would be extruded out of the contact area and bypass the flow from both sides. In this process, the oil phase mainly accumulated at the inlet of the sump, while the water phase accumulated at the edge of the oil phase and at the barren placed on both sides. Theoretical analysis showed that in the emulsion fluid dynamic pressure lubrication process, the oil phase was easier to wet the solid surface than the water phase, thus entering the contact area of the oil film to play a role in carrying, while the water phase was not easy to wet the solid surface, it was not easy to enter the contact area inside. When the speed was large when the lack of oil phenomenon, this time the size of the film thickness did not decrease but increase because of part of the water phase entering the contact zone, the contact zone inside the oil-water mixture. Theoretical calculations on the oil and water phased from the solid surface separation of the adhesion work required, the results showed that: in the fluid dynamic pressure lubrication, the oil phase molecules preferred over the water phase molecules adhering to the solid surface, the formation of effective oil film. When the emulsion was in contact with different surfaces, the more the adhesion work required to be overcome to separate the oil phase from the interface, the easier it was for the oil film to wet the solid surface in the emulsion environment, thus forming an effective oil film, and the film-forming ability of different surfaces was as follows: h_AF＞h_Steel＞h_FAS.