Wetting & Contact Angle — Young Equation

Surface Energies

γ_SV (solid-vapor): 0.50 γ_SL (solid-liquid): 0.20 γ_LV (liquid-vapor): 0.40

Cassie-Baxter

Surface roughness r: 1.00 Solid fraction f_s: 1.00

Results

Young angle θ_Y—

Wenzel angle θ_W—

Cassie angle θ_C—

Spreading S—

—

cos θ_Y = (γ_SV − γ_SL) / γ_LV

Partial wetting: 0° < θ < 180° — liquid forms a droplet.
Complete wetting: S = γ_SV−γ_SL−γ_LV ≥ 0, θ→0°.
Wenzel: roughness amplifies wettability.
Cassie-Baxter: air pockets trapped under droplet, enhanced hydrophobicity.