Determination of the nonlinearity and activation energy parameters in the TNM model of structural recovery

The structural recovery of amorphous glassy materials is nonlinear and nonexponential, and the relaxation process can be described by the phenomenological Tool–Narayanaswamy–Moynihan and Kovacs–Aklonis–Hutchinson–Ramos models. The nonlinearity parameter x in these models can be determined by several methods, including inflectional analysis, time–temperature superposition, and a new modified temperature-jump method, the latter a modification of the two-step Lagasse et al.’s method. The activation energy ∆h/R can also be determined by the first two methods. In this paper, the applicability of these methods for determining x and ∆h/R is analyzed using simulated structural recovery data as a function of aging time, after cooling at high rates such as those obtainable experimentally using Flash DSC. The results indicate that the activation energy obtained by the time–temperature superposition method is slightly better than that estimated by the inflectional analysis method. The results also indicate that the nonlinearity parameter x can be obtained by the inflectional analysis method for β = 1.0 and for low x and high β. On the other hand, the new modified temperature-jump method works for a broader range of x and β.