Surfaces 2 Gibbs Approach to Surface Energy

In the case of the polymer-air interface, the ability to stick to the surface, resist wear or have a certain aesthetic characteristic can be dependent on the way the polymer molecules are organized at the interface. A number of physical phenomena are related to our understanding of the properties of an interface spreading of oil on a surface, adhesion of two bodies in contact (e.g. chewing gum sticking to a pavement), interaction of fluids with biological materials (e.g. blood in arteries), etc. 

At a molecular scale an interface is an imbalanced system of interactions and will have an associated imbalance of chemical potential and free energy. The molecules at the air-solid surface are attracted by the molecules in the bulk and 

Similar imbalances of forces will exist at the liquid-solid and the solid-solid interfaces. In the case of the liquid-liquid or liquid-solid interfaces when the energies of the two phases approach one another then mixing can occur. If the two phases have essentially the same energy then mutual diffusion will occur and a homogeneous mixture can be created. Liquid will mix with other liquid if their energies a similar and the surface tension is low. 

---