Stability of a water droplet on micropillared hydrophobic surfaces

The stability of a droplet was influenced by the geometric parameters of micropillared surface, e.g., the height and pitch, and their relationships. Here, the effect of varying height and pitch on the wetting state of patterned hydrophobic surfaces was investigated. For a gentle deposited Cassie-Baxter droplet, it will transit to the Wenzel state with the evaporation of the droplet. Two evaporation modes (constant contact angle (CCA) and constant contact radius (CCR)) were used to determine the critical height and pitch of micropillars; when pillar height was larger than the critical value and the pitch smaller than the other one, the droplet can remain in Cassie-Baxter state well with the evolution of the droplet evaporation and, instead, the droplet cannot keep a good stability and would be transited to Wenzel state. The trends were discussed based on experimental results and then a transition criterion was proposed.