WLF Equation

Williams-Landell-Ferry Equation:

$$\log\, a_T = {{ - 17.4(T - T_g )} \over {51.6 + (T - T_g )}}$$

where

• a _T = shift factor

• T = selected temperature

• T_g = glass transition temperature

The shift factor is the shift in time scale corresponding to the difference between the selected and reference temperature, and the shift factor represents the temperature dependence of the rate of the segmental motion which underlies all viscoelastic behavior; the WLF equation demonstrates that all polymers, irrespective of their chemical structure, will exhibit similar viscoelastic behavior at equal temperature intervals (T−T_g) above their respective glass transition temperatures (T_g). (Elias, H. G., Macromolecules, Plenum Press, New York, 1977; Physical Properties of Polymers Handbook, Mark, J. E. ed., Springer-Verlag, New York, 1996) See Williams-Landell-Ferry Equation.