Chain Stretch the Doi-Edwards-Marrucci-Grizzuti DEMG Theory

2 Chain Stretch the Doi-Edwards-Marrucci-Grizzuti (DEMG) Theory 

Here and the maximum length to which a tube segment can be stretched, 

The factor of 0.82 is due to the zig-zag conformation of a fully extended carbon backbone. Lgq, the equilibrium length of a tube segment, equals Zq, where is the 

Once S and A have been obtained by solving Eqs. 11.8 and 11.9, andk5(A)ffomEq. 11.11, the stress tensor trcan be obtained from Eq. 11.10. Fortunately, the set of Eqs. 11.8 through 11.11, which defines the toy version of the DEMG theory, is nearly identical in its predictions to the fiill DEMG model. The DEMG model, in full or toy form, improves some aspects of the Doi-Edwards equation but not others. 

In fast shearing flows, with shear rates greater than I/Tj, the DEMG theory shows overshoots in both shear stress 7 and first normal stress dilference Nj as functions of time after start-up of steady shearing [21 ], in agreement with experiments (as will be presented in Section 11.5.1.1). These overshoots in both 7 and are an improvement over DE theory, which shows only the 

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