Wetting States on Circular Micropillars with Convex Sidewalls after Liquids Contact Groove Base

It is considered that the Cassie–Baxter wetting state should be transitioned to that of the Wenzel state if a water drop has contact with the base of a roughness groove. However, in recent tests on the leaf surfaces of three lotus varieties, we found that the transition did not occur. To explore the reason behind this, in this work we model the corresponding surface structures as circular micropillars with convex sidewalls, and derive an angle inequality for judging transition from Cassie–Baxter to Wenzel States. We also consider the transition on spherical microparticles, as well as that on circular micropillars with straight sidewalls. Finally, we validate the angle inequality through pressing tests on three lotus varieties and spherical microballs.