Wetting Transition — Contact Angle
Young-Dupré equation: how surface energies determine droplet shape
Surface Energies
γ_SV (solid-vapor):
0.70
J/m²
γ_SL (solid-liquid):
0.30
J/m²
γ_LV (liquid-vapor):
0.50
J/m²
Droplet volume:
1.0
--°
Contact angle θ
--
Spreading coefficient S
cos θ = (γ_SV − γ_SL) / γ_LV
Young's equation (1805)
balances three interfacial tensions at the contact line.
θ < 90°: hydrophilic (partial wetting)
θ > 90°: hydrophobic (non-wetting)
S > 0: complete wetting — droplet spreads flat
Drag the sliders to watch the droplet shape transform.