High-efficiency mechanism of enhancement of spreading performance of oil involving surfactant-laden oil droplet spreading over water surface

This study clarified the high-efficiency mechanism of enhancement of the spreading performance of oil by allowing a droplet of an organic solvent to spread over the surface of water with the addition of oil-soluble surfactants. Firstly, the effect of Span 85, Span 80, Span 20, octylphenol polyoxyethylene (4) ether (OP-4), and sodium dioctyl sulfosuccinate (AOT) on the interfacial parameters of an n-decane droplet was evaluated by measuring the surface tension and interfacial tension. Then the spreading coefficient was calculated to determine whether the surfactant-laden oil droplets could spread at the air–water interface. Moreover, the law governing the spreading of the surfactant-laden oil droplets over water was systematically studied. Furthermore, the characteristics of the dynamic behavior of the surfactants were investigated by molecular dynamics simulations to elucidate the spreading mechanism. The results of the experiments and simulations explained how the oil-soluble surfactants Span 85, Span 80, Span 20, OP-4, and AOT significantly improved the spreading performance of oil droplets over the water surface.