What if designing superhydrophobic polymer surfaces turned out to be very simple?

Various natural or artificial surface topographies or textures lead to slippery superhydrophobicity, but have little in common. Thus, simple questions need to be asked: what are the key parameters required for reaching slippery superhydrophobicity, i.e. forming a Cassie-Baxter's interface instead of a Wenzel's one? Is the double texturing scale, i.e. nano and micro, imperative to reach this superhydrophobicity regime as usually agreed upon the literature? In this paper, a simple model of the wetting of a textured surface based on the balance between the liquid pressure and the surface tension for a Cassie-Baxter's interface is described. The textured surface is sup-posed to be slippery superhydrophobic as long as a pure Cassie-Baxter's interface with a contact angle larger than 150 degrees is established. The stability limits of such an interface upon pressure are studied depending on simple parameters such as asperities shape, size, or spacing distance. Then, this model is applied on simple theoretical surfaces and its conclusions are challenged with surface wetting situations described in the literature, showing great accordance. The proposed model offers a simple understanding of the relationship between surface texture and superhydrophobicity. Such an understanding guides the design of stable superhydrophobic surfaces using simple parameters. An ideal surface texture for superhydrophobicity can be described: An intrinsically hydro-phobic surface with as small as possible re-entrant asperities that are spaced by more than their own width, and at least as high as their spacing distance.

Automated summary

This paper describes a simple wetting model based on the balance between liquid pressure and surface tension to understand the parameters required for achieving slippery superhydrophobicity. The importance of both nano and micro-scale texturing for superhydrophobicity is discussed, and the stability limits of a Cassie-Baxter interface are studied. The proposed model provides insights into the design of stable superhydrophobic surfaces.