Surfactant-assisted detachment of oil droplet from the solid quartz substrate in water

In this paper, the effect of surfactant type (cationic, anionic, nonionic, and zwitterionic) on the detachment of hexadecane droplets from the quartz surface was investigated. The results indicated that the oil detachment performance was controlled by the adsorption behavior of surfactant molecules at the interface between the solid and liquid phases, which could alter the solid–liquid interfacial tension (IFT). In the cationic solution, IFTs of solid-oil and solid-water decreased and increased, respectively, ascribed to the electrostatic attraction occurring between the positively charged hydrophilic group and the negatively charged quartz surface. Conversely, in the anionic solution, the anionic surfactant with a negative head group increased the oil-solid IFT because of its electrostatic repulsion with the quartz surface, increasing the oil contact angle and subsequently oil droplet detachment under the hydrodynamic effect. In addition, the results obtained from the adhesive force test showed that nonionic and zwitterionic surfactants had the capability of preventing the re-adhesion of solid and oil, whereas the anionic surfactant had the best performance among the four types of surfactant for oil detachment from quartz surface.

Graphical Abstract