Cassie-Baxter relation

We denote by and I the relative fractions of the solid and liquid phases underneath the drop. The Cassie-Baxter relation [equation (9.5)] can be applied to the mixed surface, with contact angles 6e and 0, respectively. We then deduce 9 ... 

Again, the surface is mixed and we can resort to the Cassie-Baxter relation [equation (9.5)] to determine the angle B. The two phases involved (solid and air) are characterized by their respective contact angles Be and tt. 

This is known as Cassie Baxter relation. The Teflon layer when deposited on a rough substrate may be porous and inhomogeneous. Hence, the wetting parameter gets modified according to Cassie-Baxter relation, and the gain in hydrophobicity is not as significant as expected. 

The second theory, the Cassie-Baxter theory [75], describes a superhydrophobic surface with contact angle, independently of the value of roughness. A surface is described as a composite material (material + air) and the water droplet interacts either with the material or the trapped air. Therefore, the contact angle relation is as follows ... 

Due to this effect, the interface and therefore adhesion between the solid and liquid are increased compared with that observed on the flat surface of the same material. (2) If the liquid wets the structured surface incompletely, a composite solid/liquid-air interface is formed. In this case the relation between the contact angle of liquid on the flat surface fh,t, the contact angle of liquid on the structured surface 0, and the ratio of the solid surface in contact with liquid is given by Cassie-Baxter equation (Cassie and Baxter, 1944) ... 

The effect of roughness on the wettability of an idealized sinusoidal surface has been studied with a digital computer. The equations of Wenzel and of Cassie and Baxter are discussed in relation to the model. The heights of the energy barriers between metastable states of a drop are seen to be of utmost importance in determining the magnitude of contact angle hysteresis. 

In the context of the fimdamental relation between surface topography and wetting behavior as modeled by Wenzel or Cassie and Baxter one has to consider the relevance of geometrical parameters for the complex porous and textured textile substrate. It is of interest in this context that a paper by Hsieh et al. [26], who studied the wetting of water and ethylene... 

Two equations due respectively to Wenzel and to Cassie and Baxter 0 are frequently quoted to determine the contact angle on a rough and on a heterogenous surface. Both equations can be derived thermodynamically (e.g. reference 10) by considering average values of the surface tensions. Wenzel s equation relates the observed contact angle, 0, measured in relation to the mean surface, to the roughness ratio r of the surface (true area divided by projected area) ... 

---