A new molecular constitutive equation for a class of branchedpolymers has been introduced by McLeish and Larson(J.Rheol. 42(1), 1998), the Pom-Pom model. Incorporating aGiesekus type of oriental diffusion in their differential form(which predicts zero $N_2$) and writing it in a closeddifferential form for the stress tensor, results in a generalizeddifferential constitutive equation. The non-linear parameterrelated to the Giesekus part of the model accounts for a secondnormal stress difference. Linear parameters are fitted to datafrom dynamic measurements, and most of the non-linear parametersto the transient uniaxial elongational data. It is demonstratedfor different polymers that with this Extended Pom-Pom model(EPP) a very good quantitative agreement can be obtained over a wide range of well defined rheometric experiments. This is exceptional and, in our opinion, shows that the Pom-Pom model is a majot step forwards in the field of viscoelastic constitutive equations.
|Title of host publication||Proc. 2nd Workshop on Inverse problems in rheology and related experimental techniques|
|Place of Publication||Germany, Badenweiler|
|Publication status||Published - 2001|