The nonlinear response of a polydisperse polymer solution to step strain deformations

The rheological behavior of a concentrated solution of well-characterized, broad molecular weight distribution polystyrene in step strain flows is exa mined at large deformations. Mechanical and optical techniques are used to obtain the full stress tensor in terms of the shear stress, first normal st ress difference, and second normal stress difference. Stress relaxation dat a on this novel system in single- and double-step strain flows over a wide range of shear strains are presented. Direct comparisons to data on a simil ar system having a narrow molecular weight distribution are made illustrati ng the effects of polydispersity on nonlinear rheological behavior. The new data set is also used to evaluate the reptation model and K-BKZ theory.