Experimentally validated phase-field model to design the wettability of micro-structured surfaces

Surfaces with tailored wettability have attracted considerable attention because of their wide range of potential applications. Wettability can be finely designed by controlling the chemistry and/or morphology of a surface. However, the commonly adopted analytical theories of Wenzel and Cassie-Baxter cannot describe a variety of intermediate and metastable states, being a thorough understanding of the combined chemical and morphological effect on surface wettability still lacking. Hence, the design and optimization of these surfaces is generally expensive and time-consuming. In this work, we propose a numerical method based on the phase-field model to predict the wettability of micro-structured surfaces and assist their design. First, we simulated the sessile droplet experiment on flat surfaces to calibrate model parameters. Second, we modelled several surface morphologies, intrinsic contact angles and droplet impact velocities. Finally, we produced and tested 3D printed flat and micro-structured samples to validate the phase-field model, obtaining a reasonable qualitative and quantitative agreement between numerical and experimental results. The validated model proposed here can help design and prototype surfaces with tailored wettability. Furthermore, integrated with atomistic/mesoscopic simulations, it represents the last step of a predictive multi-scale model, where both chemical and morphological features of surfaces can be designed a priori.