• Entropic-FV;
  • free volume;
  • Gibbs free energy;
  • polymer solutions;


A new activity model was developed with the use of the Gibbs–Helmholtz relation at constant pressure and composition. This model consists of combinatorial and residual terms. The residual term is the same as that in the UNIQUAC method, but the total area fraction of molecules is introduced on account of the hole effect. The combinatorial part takes into account the free volume (FV) effect, which plays a significant role in polymer systems. The validity of this model is demonstrated by calculating the solvent activities in 36 polymer solutions in comparison with Entropic-FV (EFV) and UNIFAC-FV methods. The total average absolute deviations (AAD) from the experimental observations are 8.27, 6.38, and 1.64 for EFV, UNIFAC-FV, and the present method, respectively. It is found that the fit to these experimental data by the present model is quite good over a wide range of concentration. An estimation of the infinite dilution activity coefficients also proves the validity of the new method. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3299–3307, 2005