Start-up and relaxation of well-characterized comb polymers in simple shear

Viscoelasticity and nonlinear simple shear flow behavior of an entangled asymmetric exact comb polymer solution

“…Subsequently, we discuss and compare the steadystate shear stress and first normal stress difference as a function of shear rate, as obtained mechanically and optically. Finally, we show that both nonlinear stresses can be quantitatively described with a tube model developed for linear polymers when treating the branches as dynamic solvent, as already qualitatively observed in [33,34].…”

“…Strong qualitative as well as quantitative differences in the nonlinear shear flow behavior only became apparent when the branches were "long" and comprise more than about 70% of the total molecular structure [63]. The exact comb structure under consideration here falls in the same category as the combs in [33] and hence modeling with a model for linear polymers is justified, although it would be unreasonable to expect quantitative accuracy. A nonlinear single-mode constitutive model that includes all of the features of the molecular theory for entangled, linear, monodisperse polymers based on the tube idea, i.e., the orientation of the tube due to the flow at rates higher than the inverse terminal relaxation time, and, at rates above the inverse Rouse time of the chain, the stretch of the chain within the tube, was developed by Marrucci and Ianniruberto in [56], henceforth referred to as the "M-I model."…”

“…For the nonlinear shear flow data instead, we attempted to describe the steady-state shear viscosity and first normal stress difference with a model for linear polymers which is justified based on an earlier work where we found that combs with relatively short branches behave essentially like linear polymers in nonlinear shear flow with some small quantitative differences [33,34]. Strong qualitative as well as quantitative differences in the nonlinear shear flow behavior only became apparent when the branches were "long" and comprise more than about 70% of the total molecular structure [63].…”

“…The zero-shear viscosity g 0 , the zero-shear recoverable compliance J S 0 , and the longest relaxation time s 0 were evaluated as discussed in [33] by fitting different models to the low frequency data. For the solution (at 20 C), we found g 0 ¼ 362 6 9 Pa s, J S 0 ¼ (1.77 6 0.09)Â 10 À4 Pa…”

“…II C. In this section, we report upon the most complete data set on the transient start-up shear flow obtained at À20 C, keeping in mind these problems and limitations. Also note that the transient start-up shear flow behavior has been studied in the CPP for a variety of combs in the molten state in [33,63].…”