Cassie-Baxter regime

The situation where the hquid does not penetrate into the spaces created by the surface roughness is termed the Cassie-Baxter regime. In this case the hquid is suspended at the tops of the surface pillars, the air-water interface is supported... 

Patterned resist surfaces exhibited air-trapping (Cassie-Baxter regime) behavior, resulting in an unexpected increase of the SACA, SRCA and DRCA with pattern depth. 

FIGURE 7.2 Wetting of a liquid drop on a textured surface, (a) Wenzel regime, (b) Cassie-Baxter regime. 

Single surfactant solutions have been studied at SH surfaces as a function of concentration and the presence of salts, with a resulting switch from the Cassie-Baxter to the Wenzel regime which is a required feature for many technological processes [4]. 

Figure 4.8 Schematics of a motion of the contact hne of a hquid droplet sitting on a solid surface, leading to a corresponding free energy variation for a smooth surface (Young model, a), complete penetration of the liquid into the recessed features of a pattern (Wenzel model, b), and for heterogeneous wetting regimes with absence of penetration (Cassie-Baxter model, c) and for partial penetration (d). In the Wenzel model, rfp = AB + BC + CD + DE)I AB + CD) according to the letters in (b). In the Cassie-Baxter model, (j) = (AB)I(AB + BE) according to the letters in (c).

In the heterogeneous wetting regime, air can instead be trapped inside the features underneath the liquid drop, which ideally stands on the top of the nanostructures. This situation (schematized in Figure 4.8c) is described by the Cassie-Baxter model. The free energy variation following the contact line displacement is ... 

---