Droplet migration on conical glass fibers

Abstract

This thesis is centered on the study of spontaneous droplet migration along conical fibers. One of the key motivations for this project was to better understand the water-harvesting mechanism used by natural organisms like cacti. These desert plants exploit the conical shape of their spines to make fog condense into small droplets at the tip of theses spines. Then, droplets will spontaneously move towards the thickest end of the spines, bringing water to the main body of the plant. The key force behind drop migration on a conical fiber has been identified as the fluid surface tension by Lorenceau an Quéré in 2004. These authors also suggested and tested a model predicting the speed of drops on conical fibers. Here, we explore a larger range of relative sizes of drops compared to the fiber radius. The present document describes how an experimental set-up was designed in order to study droplet migration with conical glass fibers and silicone oil droplets. Using optical microscopy and data analysis, the droplet speed was measured as well as the other experimental parameters. Finally, a simple theoretical model has been developed to predict the droplet speed as a function of geometrical parameters and fluid characteristics.