The Temperature Dependence of Relaxation and Retardation Times

The function ar follows the WLF equation for diluted as for undiluted systems, and several concentrated solutions were included in the summary of Table 1 l-II. In terms of Tg as the reference temperature, the WLF equation is 

Addition of a diluent of low molecular weight depresses Tg sharply, linearly at first in accordance with the equation  

The relation of Tg to fractional free volume has been treated by several authors. In the linear range where equation 2 holds, a linear dependence of/ on wi is expected  

Ppi/P2- If the glass transition is a state of iso-free-volume, it follows that in equation 2,k = j8/ /, or jS = kafP /p2- An alternative expression for jS is 

Glass transition temperatures of polystyrene solutions with various diluents of low molecular weight, plotted against weight fraction of diluent. The Tg for the undiluted polymer is somewhat lower than that usually accepted (Table 11-11). (Jenckel and Heusch. ) 

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