| Abstract: | Experimental and theoretical investigations of stress relaxation after “double-step” shear experiments lead to a better understanding of the irreversibility assumption of polymer melts. Here we compare measurements of shear stress relaxation for a branched polyethylene and a (linear) polyisobutene melt to theoretical predictions of Wagner's first and second equation and to a molecular theory of Doi. None of these theories is able to describe all the results of the measurements. These investigations demonstrate, however, what types of “double-step” shear experiments are most sensitive to the irreversible disentanglement of polymer melts. |
