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Contact Angle & Wetting Phenomena

90°
Contact Angle θ
Partial
Wetting State
0.00
Spreading Coeff. S
0.00
Work of Adhesion W_a
50 mN/m
25 mN/m
72 mN/m
1.00

Young-Dupré Equation & Wetting Thermodynamics

A liquid droplet on a solid surface adopts a contact angle θ determined by the balance of three surface tensions at the three-phase contact line:

Young's equation: γ_SV = γ_SL + γ_LV cos θ → cos θ = (γ_SV − γ_SL)/γ_LV
Spreading coefficient: S = γ_SV − γ_SL − γ_LV (S≥0 → complete wetting)
Work of adhesion (Dupré): W_a = γ_LV(1 + cos θ)
Wenzel (rough surface): cos θ_W = r cos θ_Y (r = roughness ratio)

θ < 90°: hydrophilic (wetting favored). θ > 90°: hydrophobic. θ → 0°: complete wetting. θ → 180°: complete non-wetting (superhydrophobic). Lotus effect exploits roughness to push θ > 150°.