Table 5.

Comparison of Wenzel and Cassie-Baxter models in surface wettability.

	Wenzel Model	Cassie Model
Water drop profile	The droplet fills all the grooves and valleys of a rough surface. The liquid is in full contact with the surface, enhancing the polymer’s intrinsic wettability.	The droplet rests atop the peaks of the roughness with air pockets trapped in the valleys. The rough surface is only partially wet.
Apparent contact angle (θ*)	$\cos \left(\mathsf{\theta }*\right)=\mathrm{r}.\cos \left(\mathsf{\theta }\right)$ where r is the roughness factor (ratio of the actual to the projected surface area) and θ is Young’s contact angle on a flat surface [48].	$\cos \left(\mathsf{\theta }*\right)={\mathrm{f}}_1.\cos \left({\mathsf{\theta }}_1\right)+{\mathrm{f}}_2.\cos \left({\mathsf{\theta }}_2\right)$ where f1 and f2 are the respective surface fractions in contact with the liquid and air, and θ1 and θ2 are the corresponding contact angles [48].
Notes	-If a surface is intrinsically hydrophobic (θ > 90°), roughness will enhance its hydrophobicity. -If it is hydrophilic (θ < 90°), roughness will make it even more hydrophilic.	This model is often used to explain the superhydrophobic phenomenon, as seen on lotus leaves.