Wetting characteristic of bubble on micro-pillar structured surface under a water pool

In this study, the contact angle of air bubbles on a micro-structured surface under a water pool is experimentally investigated. A previous study “Kang and Jacobi, Equilibrium Contact Angles of Liquids on Ideal Rough Surfaces, Langmuir (2011)” adopted the work of adhesion as the additional work of the process of droplet contact on a textured surface, and it explained the reason for failure of the classical theoretical model (Wenzel equation) in real wetting tests. We extended the above concept to bubble interaction with the textured surface. First, the bubble contact angles on the textured surface were modeled based on the concept of the work of adhesion in the free energy calculation. Second, the contact angle of air bubbles was measured on the bottom of test surfaces under a water pool. The test-section surfaces have micro-pillars with a size of 5-40 μm prepared by the microelectromechanical systems (MEMS) technique. The bubble contact angles were compared with both the modeled bubble shape and classical prediction (Wenzel & Cassie-Baxter equations). In addition, detail wetting features which shows wetting transition and critical wetting behavior of bubble were discussed.