Wetting & Contact Angle — Young Equation

γ_SG = γ_SL + γ_LG·cos θ — droplet shape from interfacial tensions

θ = 90° — Partial wetting
55 mJ/m²
25 mJ/m²
40 mJ/m²
1.0
Young's equation (1805): force balance of three interfaces at the contact line. cos θ = (γ_SG − γ_SL)/γ_LG. θ < 90°: hydrophilic wetting; θ > 90°: hydrophobic; θ = 0°: complete wetting (spreading coefficient S = γ_SG − γ_SL − γ_LG > 0); θ = 180°: perfect non-wetting.