Flory–Huggins solution theory

Summary

Flory–Huggins theory is a lattice model of the free energy of mixing of a polymer with a solvent, or of two polymers. It counts the ways to place chains on a lattice, which gives an entropy of mixing much smaller than for small molecules. It adds a mean-field interaction energy measured by one parameter $\chi$. From the resulting free energy one reads off when the mixture is stable and when it separates into two phases. It is the starting point of the theory of polymer solutions and blends.