An excess Gibbs energy model to study the phase behavior of aqueous two-phase systems of polyethylene glycol+dextran

A new model for the excess Gibbs energy named UNIQUAC-NRF is presented to study the phase behavior of aqueous two-phase polymer–polymer systems. The assumptions of the NRTL-NRF model and the local composition expression of the UNIQUAC model have been used in the development of the new model. Using the random state as a reference state, a model for gE as function of the nonrandom factor has been developed for binary and multicomponent mixtures. w model was applied for the prediction of the phase behavior of aqueous two-phase polymer–polymer systems of polyethylene glycol+dextran. The interaction parameters were obtained for 25 systems. Comparing the results of the UINQUAC and UNIQUAC-NRF models, it was shown that the present model is more accurate.