hydrophobic droplet

Author: ekaterine dadiani
Keywords: droplet, hydrophobic, oscillation
Annotation:

We consider the problem of small drops’ oscillation on a vibrating surface of the same liquid under certain conditions. This phenomenon is observed because compressed air layer between two surfaces gives enough pressure to lift the drop. For some parameters drop starts bouncing and therefore air film is periodically renewed which leads to long time oscillations without coalescence. Force induced from compressed air layer is found theoretically according to Reynold’s lubrication theory. Droplet’s Lifespan dependence on relevant parameters (such as surface tension, viscosity, droplet’s radius, oscillation frequency) is examined both theoretically and experimentally and they give a good agreement with each other. So the main peculiarity of this problem is the explanation and investigation of non-coalescence of the same liquids on a vibrating surface, but there are interesting phenomena which are also worth to examine. For example if we inject more fluid into oscillating drop and increase its size considerably, it will submerge into the vibrating liquid and may last few seconds or minutes without coalescence even if the surface stops oscillations. In this case as air starts to flow out from the sides of the droplet, the thickness of air layer between the droplet and liquid surface decreases and when surfaces approach each other enough for the Van der Waals forces to activate, the drop coalesces with the liquid. The time needed for this to occur is found theoretically and is compared to experiments for different parameters. Another effect is observed when there are two or more drops on the vibrating surfaces, for different conditions they may attract or repulse each other that we explain by minimizing of surface energy and theoretical assumptions are in good agreement with experiments.