A local composition model is developed for the representation of the excess Gibbs energy of polymer solutions. The model consists of two contributions due to the configurational entropy of mixing, represented by the Freed Flory-Huggins relation, and to the enthalpic contribution, represented by local compositions through nonrandom factor. The model is applied to correlate the solvent activity of binary polymer solutions. The new excess Gibbs energy equation was used along with the absolute rate theory of Eyring for modeling the dynamic viscosity of binary polymer solutions in the entire concentration range at different temperatures considering different molar mass of polymers. The fitting quality of new model has favorably been compared with polymer-NRTL, segment-based-liquid-NRTL, polymer-Wilson, polymer-NRF and polymer-NRF-Wilson models. The validity of the proposed model is especially demonstrated for the whole range of polymer concentrations at different temperatures using different molar masses of polymers. The segment-based approach provides a more physically realistic model for large molecules when diffusion and flow are viewed to occur by a sequence of individual segment jumps into vacancies rather than jumps of the entire large molecule. Therefore, the correlation of viscosity values for nanofluids was also tested with the proposed Eyring-modified NRF model developed with respect to the segment-based approach. The performance of this model in the fitting of viscosity values of nanofluids are compared with the previously used liquid-NRTL model. Results show that this segment-based model is most valid in the fitting of viscosity values of nanofluids in the entire concentration range at different temperatures.