Analytical modeling of superhydrophobic surfaces with the microstructures composed of fibers and hemispheres

Superhydrophobic surfaces have been fabricated in large quantities via designing suitable micro/nano structures and introducing low surface energies. However, the thermodynamic mechanisms between superhydrophobicity and microstructures still need to be further investigated to better provide a guidance for achieving superhydrophobicity. In this work, a theoretical model based on an actual coating with the microstructures consisting of fibers and nano hemispheres was constructed to analyze the effects of structural parameters on contact angles and free energies, where three wetting phases were defined according to different wetting heights of droplets on the surface. By calculations, the wetting equilibrium states and their corresponding contact angles and structural optimization strategies in the three wetting phases were obtained. Besides, the superhydrophobic coating prepared using magnesium oxysulfate whiskers and SiO2 nano hemispheres was used as an example for the model application. The results of the model analysis showed that there should be two equilibrium states of water droplets on the coating surface. This study is expected to be utilized to guide the design of superhydrophobic surfaces.