The Flory-Huggins model may be considered a correction to Regular Solution theory for the entropy effect from mixing molecules of greatly differing size. Therefore this model is useful for modeling polymer/solvent systems, especially if the molecules are non-polar.
If no binary parameters are supplied, the Flory-Huggins equation calculates the liquid activity coefficient by applying a correction factor for liquid volume differences to the activity coefficient computed by the Regular Solution method.
Refer "Flory-Huggins Theory" under "Liquid Activity Coefficient Methods" in the PRO/II Reference Manual, Volume I, Chapter 2 for more information on this method.
Pure Species Parameters for Polymers