The rheological behavior under simple shear for a wide number of Newtonian fluids has been accurately described by the friction theory, from pure compounds to complex mixtures such as petroleum fluids. Recently, this approach has been further extended to the modeling of the non-Newtonian behavior found in waxy-heavy oils. Thus, the f-theory is now capable of reproducing the viscosity reduction with the shear-rate and additionally, the presence of the two Newtonian regions, located at low and high values of the strain-rate. This has been achieved for reservoir fluids using cubic equations of state, widely used in the oil industry, with the friction theory.

The extension to polymeric systems requires the use of a more advanced fundamental model intended for chain molecules, such as the PC-SAFT equation of state. A shear-thinning viscosity is typically observed in concentrated polymer solutions. Initial results using the PC-SAFT friction theory successfully described the rheological behavior of polystyrene/polystyrene systems and notoriously predicted the rheological behavior of polystyrene/carbon dioxide mixtures. On the basis of these encouraging results, the generalization of the f-theory approach to additional polymer systems is further examined.