Dynamics of acoustically levitated drops with Ouzo effect

Ouzo effect represents a typical spontaneous emulsification process, which is widely used in many fields such as chemical industry, biomedicine and fabrication of novel materials. This work attempts to clarify the influence of sound field and container-free conditions on Ouzo effect by combining Ouzo transition with the action of sound field. We compare the dynamic process by performing experiments on a glass slide and in an acoustic levitator, respectively, through triggering Ouzo effect via evaporation and droplet coalescence. We observe the evaporation-induced Ouzo transition, and the growth of emerged oil droplet satisfies the Fick’s law suggesting the droplet growth is dominated by diffusion. Under acoustic levitation, the Ouzo effect driven by droplet evaporation produces small droplets of divinylbenzene that rapidly diffuse with convection in the droplet and distribute uniformly throughout the droplet until only continuous droplet remains. Droplet coalescence could result in Ouzo transition and lead to the abnormal shape of levitated drop, which contains micron-sized oil droplets under acoustic levitation. By decreasing the intensity of sound field, the Ouzo droplet returns to an axisymmetrical shape and then recovers to its initial shape upon enhancing the sound intensity, indicating that the flow field in the droplet plays an important role in maintaining the irregular shape of Ouzo droplet. The abnormal shape of droplet is caused by both the internal flows and the acoustic radiation pressure exerted on the drop surface. This study may shed light on the developing of new techniques for micro-emulsification and fabrication of related materials.