Effect of Pressure on the Viscoelastic Response

While an increase in temperature speeds up the viscoelastic response, an increase in pressure slows it down. In the so-called piezorheologically simple systems, all the response times have the same dependence on pressure, and the generalized shift factor is expressed by the Fillers-Moonan-Tschoegl equation (17) 

In this latter equation, Pq is the reference pressure and P is the experimental pressure. Obviously, Eq. (8.41) reduces to the WLF equation when P = Pq. 

6 DIFFERENTIATION OF REGIONS IN THE MASTER CURVES OF THE VISCOELASTIC FUNCTIONS 

The use of the term glassy-like for this zone arises from the fact that the viscoelastic mechanisms associated with the response are believed to involve local motions, such as occurs in the glassy state. The response in this region is independent of molecular weight, and the creep comphance function obeys Andrade s equation (18,19) 

The tangent of 8 exhibits a prominent peak in this region, and the viscoelastic loss functions G (co) and J m) may also exhibit an absorption in the transition zone. The relative location of the maxima of the loss functions G (co) and if they exist, can be obtained by taking into 

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