Thermodynamics
The shape of a liquid/vapor interface is determined by the Young–Laplace equation, with the contact angle playing the role of a boundary condition via Young's Equation.
The theoretical description of contact arises from the consideration of a thermodynamic equilibrium between the three phases: the liquid phase (L), the solid phase (S), and the gas/vapor phase (G) (which could be a mixture of ambient atmosphere and an equilibrium concentration of the liquid vapor). The “gaseous” phase could also be another (immiscible) liquid phase. If the solid–vapor interfacial energy is denoted by, the solid–liquid interfacial energy by, and the liquid–vapor interfacial energy (i.e. the surface tension) by, then the equilibrium contact angle is determined from these quantities by Young's Equation:
The contact angle can also be related to the work of adhesion via the Young-Dupré equation:
where is the solid - liquid adhesion energy per unit area when in the medium V.
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