Persisting Water Droplets on Water Surfaces

Abstract

Droplets of various liquids may float on the respective surfaces for extended periods of time prior to coalescence. We explored the features of delayed coalescence in highly purified water. Droplets several millimeters in diameter were released from a nozzle onto a water surface. Results showed that droplets had float times up to hundreds of milliseconds. When the droplets did coalesce, they did so in stepwise fashion, with periods of quiescence interspersed between periods of coalescence. Up to six steps were noted before the droplet finally vanished. Droplets were released in a series, which allowed the detection of unexpected abrupt float-time changes throughout the duration of the series. Factors such as electrostatic charge, droplet size, and sideways motion had considerable effect on droplet lifetime, as did reduction of pressure, which also diminished the number of steps needed for coalescence. On the basis of present observations and recent reports, a possible mechanism for noncoalescence is considered.

Surfing of drops on moving liquid–liquid interfaces

“…When a liquid drop falls on the surface of its homophase, coalescence is expected to occur (Charles & Mason 1960;Klyuzhin et al 2010). Coalescence of drops is ubiquitous in nature as well as in industrial applications such as transportation of oil mixtures with water (Venkataraman et al 2013;Farhadi et al 2016), milk processing (Tcholakova et al 2006), spray painting (Dalili et al 2017) and drug encapsulation (Andrade et al 2015).…”

Escape dynamics of liquid droplets confined between soft interfaces: non-inertial coalescence cascades

“…So-called partial coalescence and coalescence cascades have been observed for droplets contacting other droplets or flat liquidliquid or liquid-air interfaces. [32][33][34][35][36][37][38][39][40][41][42][43][44] 45 Sartor and Abbott and Beard et al considered the effect of dissimilar electrical droplet charges on the coalescence of colliding droplets and found that charge differences promote complete coalescence. [46][47][48] Ristenpart et al studied the droplet rebound from a liquid-liquid interface subject to an applied perpendicular electric field.…”

Wenn Wasser tanzt: Das Phänomen der hüpfenden Wassertropfen

“…Dieses Phänomen begründet die sogenannte Verweilzeit eines Tropfens, also wie lange dieser auf einer Oberfläche der gleichen Flüssigkeit verweilen kann, bevor er mit ihr verschmilzt (Abbildung ). Die Existenz einer Luftschicht kann einfach nachgewiesen werden, indem man den Luftdruck um das Experiment verringert, wodurch die Verweilzeit sinkt, da weniger Luftmoleküle zur Bildung der Schutzschicht zur Verfügung stehen . In Bezug auf unsere tanzenden Wassertropfen ist es jedoch verwunderlich, dass eine solche dünne Luftschicht intakt bleiben soll, wenn der Tropfen aus signifikanter Höhe wie dem Duschkopf und damit mit entsprechender kinetischer Energie auf die Wasseroberfläche trifft.…”