Figure 2
From: Contact Angle Measurement of Small Capillary Length Liquid in Super-repelled State
Sessile drops of two liquids with very different capillary lengths l cap and same large contact angle. (a) Droplet profiles of water and FC-72 drawn from numerical integration with apparent contact angle θ * = 150°. Comparing the water droplet and the small FC-72 droplet in the middle, they share the same Bond number (Bo = 0.73) and thus the same profile shapes, but the FC-72 droplet is smaller due to its smaller l cap. Comparing the water droplet and the large FC-72 droplet on the right, they share the same contact radius (r c = 1.5 mm), but the FC-72 droplet is flattened more due to its smaller l cap. Now, comparing the two FC-72 droplets, notice their equator heights h are similar despite a large difference in their volumes. This departure between h, which determines the image resolution, and the droplet size, which is commonly used to decide the resolution, leads to the common inaccuracy, which we propose to correct. (b and c) Relation between h and l cap from the theoretical profiles of 13 different liquids selected for experiments in this paper. The red lines show the linear fitting. The insets show the droplet profiles under their respective boundary conditions. In (b), water and FC-72 are compared with Bo = 0.73, i.e., the left and middle droplets in (a), over 0.42 mm < r c < 1.5 mm. In (c), water and FC-72 are compared with r c = 1.5 mm, i.e., the left and right droplets in (a), over 0.73 ≤ Bo ≤ 17.
