Effects of Temperature and Pressure on Relaxation Times

Interrelation of Effects of Temperature and Pressure on Relaxation Times 

Although the effect of combined temperature and pressure changes on the shift factor ot,p is complicated if the nonlinear pressure dependence of/ is taken into account, as seen in equation 57, a simple formulation is obtained in the linear range where 8/ is constant the difference between and fi in equation 49 is given by 

If the free volume is maintained constant by appropriately increasing both T and 

11 -11. Data of Fig. 11-10 (isothermal) and others at different temperatures down to — 15 C (isobaric) reduced to 2S°C and I bar by shift factors aT,p whose magnitudes are indicated in the three-dimensional insert. (Fillers and Tschoegl. ) Reproduced by permission from the Transactions of The Society of Rheology. 

a 12 should remain unity with no change in relaxation times differentiation of equation 58 with fi=f gives for this condition 

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