Self-stabilization of droplet clusters levitating over heated salt water

Inversion of Stabilized Large Droplet Clusters

“…Figure a shows the normalized temperature profile T̅ surf ( r )= T surf ( r )/ T surf (0) of the water surface, obtained using thermal imaging. (images of a typical thermal field are presented in refs. , ) A central part of this profile is reproduced in Figure b, where the radii of different clusters are also shown. It is obvious that even for the smallest cluster (Figure , N = 21) the temperature of the water surface is not entirely uniform: under the droplets in the outer layer, it is approximately 1.7% lower than the maximum temperature.…”

“…The cluster was “printed” from ultrapure deionized water (Sartorius Arium Mini Plus purification system, Germany) through the injection of microdroplets (about 30 μm in diameter) with a MicroFab Technologies, Inc. piezoelectric dispenser (USA). To analyze images of droplets, a special computer program was used, , which allows for tracking droplets and measuring the geometric parameters of the cluster, in particular, the diameter of the droplets.…”

“…To do this, it turned out to be sufficient to add a small amount of salt to the layer of water under the cluster. This amazing effect is described in, where a quantitative physical model of the process is proposed. However, infrared heating remains the main and most universal method for stabilizing droplet clusters.…”

Fluorescence profiles of water droplets in stable levitating droplet clusters

“…The experiments were performed on a laboratory setup described recently by Fedorets et al 9,24 A thin layer of water in the central part of the cuvette was heated from a substrate illuminated from below by a laser beam with adjustable power of radiation. The working volume of the setup with the main elements, including external infrared radiation to stabilize the droplet sizes 25,26 is shown schematically in Fig.…”

“…An alternative method is when independently generated small droplets are delivered to an area above a heated water layer, where the droplets form a levitating cluster and grow due to the condensation of the vapor from an upward flow of humid air. The latter method has already been used by Fedorets et al 9 to study the first observed self-stabilization of a cluster of pure water droplets levitating over a layer of water containing a small amount of salt. The obvious advantage of such a more flexible procedure compared to the spontaneous formation of a droplet cluster over the heated water surface is that it is possible to generate clusters with droplets of different chemical compositions.…”