Influence of Temperature on Horizontal Shift Factors

If the time-temperature correspondence principle holds, Eq. (8.35) suggests that the temperature dependence of the shift factor in the time (or frequency) domain can be written as 

The parameters of the VFTH equation can be calculated from the values of Ci and C2 by using the expressions of Eq. (8.39). An alternative way of obtaining m and is to plot Inaor versus / T — Too) and determine by trial and error the value of Too that best fits the plot to a straight line. It should be pointed out that in most cases Tg — 50 K. By comparing Eqs. (8.33) and (8.35), the volume fraction and the coefficient of expansion at 7k are given by (16) 

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