Validity of a macroscopic description in dilute polymeric solutions

Derivation of macroscopic equations from the simplest dumbbell models is re visited. It is demonstrated that the onset of the macroscopic description i s 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 .