Giant Drop Levitating over a Moving Wall

Abstract

We develop a novel equipment that levitates giant drops, size of which is larger than the capillary length, over a moving wall. Generally, the levitation of giant drops is challenging since a drop larger than capillary length deforms and breaks up easily. We overcome this difficulty by equipping a special-shaped glass hollow cylinder. The novel equipment successfully levitates a drop of 5 ml in volume, which is more than 500 times larger than volumes of levitating drops reported in previous works. Remarkably, the giant drop levitates more than 24 hours for the special-shaped cylinder and a liquid film over the cylinder surface. This containerless manipulation of giant drops may open a new door for new method of material science and high-precision chemical analysis. In addition, we investigate the levitation mechanism of a giant drop over a moving wall. We adopt interferometry to observe the bottom shape of the drop which is complex because of the air flow between the drop and the moving wall. It is found that, when the drop size is large enough, the bottom shape of the drop shows surface waves, which has not been reported by any previous researches. Phase speed and wavelength of the surface wave vary with experimental parameters (i.e. wall velocity and drop diameter). Interestingly, both phase speed and wavelength have a linear relationship to the product of wall velocity and drop diameter.