Temperature dependence of viscoelastic relaxations

As eqs. (5.20) and (5.21) show, and as depicted in Fig. 5.4, the forms of the relaxations in compliance and modulus are governed by the rotary frequency co, which demonstrates a principal method of the experimental probing of the 

5 Change in the storage modulus // and tan S = // /// with temperature at constant frequency v = 1.0 Hz in PMMA, showing the a-relaxation at Tg of 110 °C and p-relaxations at around 55 C at this frequency (from Schmieder and Wolf (1953)). 

The more direct identification of the molecular character of a secondary relaxation or information regarding the processes that are involved in the a-relaxation requires more information of a kinetic nature. This is accomplished by complementary experiments under different frequencies of probing to observe a temperature shift of the specific relaxation or by conducting stress-relaxation experiments at different temperatures and noting related shifts in the relaxation time of the specific transition. We explore these shifts in the following sections. 

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