Stretch regimes

Figure 3 Predicted steady-state shear stress as a function of shear rate for values of the CCR rate paramenter Cy = 0,0.01,0.1,1. The inset displays the shear stress and normal stress transients in the limit of high shear rate (within the zero-stretch regime). The results displayed are extrapolations from numerical calculations on finite chain lengths n to the limit of large n ...

In this stretched regime, the shape of the curve of the segment density distance from the surface is essentially flat, except for two adjustment regions at each end of the chains (see Fig. 4.16b). In the region within each blob (lstill applicable. For x>D, which is constant. 

As we can see from Eqs. (32), Xg in the reptation-without-stretching regime N0 <1, while XE NB-Hn NB ) for the very large "plateau molecules. This important change in behaviour indicates that the field-induced disengagement time Xg is less molecular-size dependent but more field dependent for larger molecules. 

A general observation is that all spherulites become visible at approximately the same time (within a few seconds after the cessation of flow) and that their diameters are nearly equal. A possible explanation is that flow interferes with the ability of chains to be arranged in folded-chain lamellae. Consequently, during the flow, FIPs are created but are not easily nucleated. This agrees with the experimental results of Blundell et al. [164, 170], which showed that, for strain rates higher than the inverse of the stretch relaxation time, crystallization did not start until after the cessation of flow. Therefore, Steenbakkers and Peters (whose experiments were indeed in the chain stretching regime) implemented a step function to model the effect of flow on the nucleation process, as shown in Table 14.1. 

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