Oil Marbles on Water Interface

Rainbow-type interference is a ubiquitous part of our daily life, explaining colorful oil spillage or a sunlit soap bubble. When light strikes a thin surface with thickness smaller than the wavelength of light, the reflected light waves from upper and lower boundaries of the surface can reinforce each other, giving rise to an intensified color depending on the surface’s thickness. A thin aqueous film with a varied thickness or curvature-like bubble can lead to the formation of colorful patterns. Based on the same mechanism, an oil spill on water exhibits fringes due to its uneven thickness and different refractive indexes compared to water and air. In recent years, a large number of studies have been focused on removing oil spills due to their damage to the ecosystem. Having detailed information about the evolution and dynamics of oil droplets at the water-air interface by the presence of active molecules enables experts to propose better strategies to these efforts. The presence of surface-active agents promote the spreading of oil and increase the frequency of coalescence events between them, leading to faster formation of oil films. The current snapshot demonstrates how tiny oil droplets float and merge at the water-air interface.