Viscoelasticity thermorheological characterizations

We have characterized these polymers with respect to their thermorheological response in tension, in the linear viscoelastic regime. Then their performance in a shape-memory sequence was computed from the theory of temperature-dependent linear viscoelasticity, allowing comparisons to be made between them [63]. 

When polymer blends and alloys are considered, a problem arises for the application of the principle of temperature-time superposition to the systems consisting of two and more phases. A variant of this superposition has been proposed for such materials [175]. The main feature of the temperature-time reduction in this case is the dependence of the reduction coefficient on the variables—temperature and time. The expression for the reduction coefficient may be obtained via the Taylor expansion of the relaxation function with respect to variable t and T. Phase-separated IPNs relate to thermorheologically complicated materials, hi principle, in these systems two different mechanisms of relaxation exist, each of them being characterized by its own temperature coefficient. Because of this, the application of traditional temperature-frequency superposition to IPNs is restricted. However, even in those cases when this approach is not entirely vahd, it may be used for approximate calculations. Thus, the apphcation of the temperature-time superposition to heterogeneous polymeric materials shows that the method may be very valuable for prediction of the viscoelastic properties, in spite of the necessity of further developing the theory. 

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