Meniscus-induced motion of oil droplets

Although the magnitude of the surface tension is often negligible in macroscale, capillarity-induced phenomena play an essential role in driving the motion of droplets. In this study, we conduct several experiments on the motion of an oil droplet near the meniscus between the wall and the horizontal water surface. The two cases when the water is pure and when it contains surfactant are both investigated. The results show that the oil droplet is repelled by the meniscus when the water does not include surfactant, and on the opposite it is attracted to the wall when there is surfactant added in water. We then carry out force analysis and energy simulation, which verify the experimental observations. These analyses provide inspirations for the design and fabrication of microfluidic devices, microreactors, and chemical sensors, and also pave a new way to oil collections in petroleum engineering and biomimetic design. (C) 2015 Elsevier B. V. All rights reserved.