Cassie-Baxter Transition: Gibbs Energy Analysis and CFD Simulations Using Newly Developed, Validated Algorithms

A liquid droplet on a textured substrate equalizes into either the Cassie-Baxter, or Wenzel state. In addition, metastable states between these conditions are reported in the literature. The Cassie-to-Wenzel transition has been understood as the intersection of the Cassie-Baxter and Wenzel equations, which are functions of the Young’s angle; however, a major issue exists: the texture shape and dimensions are not considered. What’s more, the transition point of the Young’s model has not been experimentally verified. Because changing texture dimensions will also cause the droplet to transit from one state to another, we plan to build a new transition model through a Gibbs energy analysis of a liquid-gas-solid system. The Young’s angle is held constant and the wetting phenomena are computed as a function of texture dimensions. Each dimension set will have an equilibrium state identified by its penetration depth and apparent contact angle. Lastly, the energy barrier describing the obstacle to a droplet moving from a meta-stable state toward the stable state can simultaneously be computed. Our newly developed, experimentally validated CFD method will be used to confirm our Gibbs energy analysis, and to explore the dynamic behaviors of a droplet during the Cassie-to-Wenzel transition.