The surface tension (γ) of a material is directly related to its intramolecular and intermolecular forces. The stronger the force, the greater the surface tension. This can be modeled by an equation:
Where ΔU is the energy of vaporization, N is the Avogadro constant, and a is the surface area per molecule. This equation also implies that the energy of vaporization affects surface tension. It is known that the stronger the force, the higher the energy of vaporization. Surface tension can then be used to calculate surface energy (u). An equation describing this property is:
Where T is temperature and the system is at constant pressure and area. Specifically for hydrogels, the free surface energy can be predicted using the Flory–Huggins free energy function for the hydrogels.
For hydrogels, surface tension plays a role in several additional characteristics including swelling ratio and stabilization.