(63a) Explaining the Wetting Stability and Robustness of the Cassie-Baxter State on Reentrant Micropatterned Surfaces Using Theoretical Analysis and Continuum Simulations

Surface wettability has been a long-studied research topic and worked as a solution to a broad spectrum of engineering problems. In this work, a theoretical Gibbs energy model has been developed for a series of reentrant micropatterned surfaces to explore the phase transitions of wetting states. The energy barriers from the Cassie-Baxter state to the Wenzel state and vice versa are theoretically computed, aiming to design more robust superhydrophobic surfaces. A three-dimensional wetting process of a 3-μL water droplet was simulated in three different modes using OpenFOAM. First, at zero gravity, the droplet was initialized in the Cassie or Wenzel state on the micropatterned surface and was relaxed to a steady state. Second, using a controlled body force, the droplet was pushed from the Cassie to Wenzel state or pulled from Wenzel to Cassie state, respectively, to estimate the energy barriers of the two transitions. Finally, the droplet impacts on the micropatterned surfaces were simulated at different initial velocities. The comparisons showed good agreement between our theoretical model and continuum simulations. This study has also revealed the mechanistic explanations for the robustness of the Cassie state on the reentrant micropatterned surfaces, i.e., the contribution of the sharp increase in the Gibbs energy, which will help the design of more robust superhydrophobic surfaces.