Examination of the validity of the Flory–Huggins solution theory in terms of miscibility in dextran systems

The validity of the original Flory–Huggins theory was examined in terms of predicting molecular miscibility in carbohydrate polymers using dextrans as model system. The solubility parameter of the monomeric unit of dextran was calculated from two different group contribution methods using the molecular structure. A predictive methodology to calculate the solubility parameters of dextrans with different molecular weights as a function of their glass transition temperatures was presented, with an inverse relationship between molecular weight and solubility parameter. The calculated solubility parameters were then used to predict the free energy of mixing two dextrans with molecular weights of 1000 and 2,000,000. The Flory–Huggins theory was demonstrated to be unsatisfactory for predicting miscibility in carbohydrate systems since it underestimates the presence of strong specific intermolecular interactions, such as hydrogen bonds, which may enhance the actual miscibility in such systems and which should be handled by more advanced thermodynamic models.