Master curves, rheological measurements

Finally we compare the temperature dependencies reported for the structural relaxation and the self-motion of hydrogens studied by NSE. For PI, the shift factors used for the construction of the master curve on Q,T) (Fig. 4.17) are identical to those observed for the structural relaxation time [8]. This temperature dependence also agrees with DS and rheological studies. The case of PIB is more complex [ 147]. The shift factors obtained from the study of Teif(Q>T) (Fig. 4.14b) reveal an apparent activation energy close to that reported from NMR results (-0.4 eV) [136]. This temperature dependence is substantially weaker than that observed for the structural relaxation time (=0.7 eV, coinciding with rheological measurements) in the same temperature range (see Fig. 4.20). 

Our method, then, provides a rheological criterion for measuring the effect of a graft copolymer on a continuous matrix. As was discussed above, the master curves relative to a reference temperature and rubber content ... 

Since the interface strength does not depend on the rate of peel, the shape of the peel master curve must arise from the rate dependence of the properties of the adhesives and we would like to be able to predict it from rheological measurements. 

Although difficult, it is possible to measure stress vs. strain curves of PSAs. Examples of such work include that of Christenson et al. [.3J and Piau et al. [23J. One can do this at various elongation rates and temperatures and create a material response function. Of course, it is much easier to obtain rheological data at small strains than to obtain tensile stress-strain data. One can assume a shape of the stress vs. strain function (i.e. a constitutive relationship) and then use the small strain data to assign values to the parameters in such a function. In order for a predictive model of peel to be useful, one should be able to use readily obtained rheological parameters like those obtained from linear viscoelastic master curve measurements and predict peel force master curves. 

Therefore plotting Is/s/iCa X ) versus CaA°- yielded the universal nonlinear master curve for dilute emulsions shown in Fig. 6. In the plateau region this curve gives a quantitative relation between the droplet parameters and the measured nonlinear rheological parameter = l5plYo according to Eq. 13 for small deviations from the linear regime. This relation can be used to extract the... 

If normalized shear stress c/Go and shear rate yxR are introduced, it is possible to summarize the overall nonlinear rheological behavior measured at different concentrations and temperatures on a master dynamic phase diagram as shown in Fig. 12 [137]. The flow curve at 21 wt. %, a concentration close to the I-N transition, makes the link with the concentrated regime. As concentration decreases, stress... 

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