Flory-Huggins Polymer Mixing

Free energy of mixing ΔG/nRT

Chain length N 50 Interaction χ 0.50 Temperature T/Tc 1.00

Spinodal:

Binodal:

Phase state:

ΔG/nRT = φln(φ)/N + (1-φ)ln(1-φ) + χφ(1-φ)

The Flory-Huggins theory describes mixing thermodynamics of polymer solutions. The entropic gain (logarithmic terms, scaled by 1/N for long chains) competes with enthalpic interactions (χ parameter). Large N drastically reduces entropy, making polymers much harder to mix than small molecules. The spinodal boundary (∂²G/∂φ²=0) marks the limit of metastability; the binodal (common tangent) gives the true equilibrium phase boundary.