 Flory–Huggins solution theory

Flory–Huggins solution theory is an incompressible lattice description of mixing a polymer with a solvent. A chain occupies $N$ connected sites, while a solvent molecule occupies one; the displayed mixing free energy is per site. The first two terms are translational entropy of mixing contributions and the last is a mean-field excess contact interaction. A positive interaction parameter $\chi$ penalizes polymer–solvent contacts. If the site volume is $v_0$, the physical free-energy density is $f/v_0$ and the polymer volume fraction gives monomer number density $\varphi /v_0$. Composition-dependent interaction parameters require extra derivative terms in stability calculations.

Flory–Huggins solution theory is a model that describes the thermodynamics of mixing in polymer solutions and blends. Developed independently by Paul J. Flory and Maurice Huggins in the 1940s, the theory provides a framework for understanding how polymers interact with solvents and with each other when they are mixed.