Validity of a macroscopic description in dilute polymeric solutions

Derivation of macroscopic equations from the simplest dumbbell models is revisited. It is demonstrated that the onset of the macroscopic description is sensitive to the flows. For Peterlin’s approximation [Makromol. Chem. 338, 44 (1961)] to Warner’s finitely extensible nonlinear elastic spring-force model [Ind. Eng. Chem. Fundam. 11, 379 (1972)] (FENE-P), small deviations from the Gaussian solution undergo a slow relaxation before the macroscopic description sets on. Some consequences of these observations are discussed.