Relaxation time Vogel-Tamman-Fulcher temperature

The relationship between the relaxation time and the temperature between glass transition and melting is described by several empirical equations. The one of the most commonly employed Vogel-Fulcher-Tamman (VFT) equation is given by (Mauro etal. 2009 Yu 2001)... 

However, as anticipated above, the glass transition phenomenology involving structural processes in polymer materials rarely follows simple Arrhenius laws, and especially near Tg (where decreasing the temperature by 10 K can produce an increase of x and r of, say, three orders of magnitude), the dramatic increase of the viscosity and of the characteristic structural relaxation time is much better described by the Vogel-Fulcher-Tamman (VFT) equation ... 

The lineshape of the VII spectrum s dominant mode was obtained by Koch, et al. (4) for 23 and 48 kDa polystyrenes in cyclohexane at concentrations 690-810 g/l. Their field correlation functions were accurately described by a Williams-Watts function exp(—(t/r) ). For a 700 g/l solution, = 0.4 was independent of temperature for 21 < T < 52°C. The mean relaxation time (tv//) = for depolarized scattering had the Vogel-Fulcher-Tamman temperature dependence... 

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