A3 Elements of thermomechanical analysis in polymer science

If the sample is a perfectly viscous liquid, the Newton law applies, i.e. stress is proportional to the strain rate. In a dynamic test stress and strain rate show a n/2 phase shift  

Viscoelastic materials show an intermediate behaviour with the angle phase shift, 5, in the range 0 - nil. In this case it is expedient the use of complex number notation for G  

G is therefore referred to as the vectorial sum of two orthogonal components, namely, the storage modulus G (the elastic component), and the loss modulus G  

In some experimental methods, like DTMA, where temperature can be varied more easily than frequency the traces observed are plots of isochrone data, obtained at a given frequency, v, versus / . Traces obtained at different frequencies are not super-posable to one another by shifting along the temperature axis, since ai does not depend linearly on 7 (see below). However an isochrone trace c in be transformed into an effective isotherm, at T = To, simply by replotting the data versus (vxa,). 

When the experimental trends do not allow such matching, it can be argued that a single friction coefficient cannot describe all the motions within the system under consideration. 

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