The transport of a wettable sphere through a fluid-fluid interface : low Bond numbers (ENHANCEMENT)

Abstract

We report on the transport of a rigid sphere through the fluid-fluid interface of a demixed colloid-polymer mixture. The sphere is wettable by the colloid-rich phase it is transported to. The ultra-low interfacial tension in these phase separating mixtures results in wetting forces that are low enough to access the low-Reynolds regime. Moreover, it enables the investigation of the role of capillary waves. Rigid spheres of various sizes approach the interface by sedimenting through the polymer-rich phase toward the interface and are subsequently transported to the colloid-rich phase. Three consecutive stages can be distinguished: (i) drainage of the continuous film between the sphere and the interface, (ii) transport of the sphere through the interface and (iii) the movement away from the interface. Depending on the Bond number, which may be viewed as the ratio between gravitational force acting on the sphere and the capillary force, different transport configurations are observed. In this chapter, the drainage configuration with a dominant capillary force is discussed. The case of a dominant gravitational force is described in the next chapter.