Activation energy for viscoelastic relaxation

Fig. 19.5. Relationship between the activation energies for viscoelastic relaxation (ilHuA/i ) measured by dynamic mechanical relaxation spectra and those for molecular transport (ilEg) in crystallization for poly(ethylene tetrephthalate) (PET) / poly(l-4-cyclohexylene dimethylene terephthalate) (PCT) copoljmers [48]. Copolymer compositions (PCT/PICT) = 1 100/0, 2 80/20, 3 66/34, 4 5/95, 5 0/100...

It follows from this treatment that the magnitude of the temperature derivative of fo is smaller for very low molecular weights than for high (when compared at the same temperature), and that the molecular weight average which controls this effect is Jf . Thus, for example, the apparent activation energy for viscoelastic relaxation at a temperature To can be expressed by combining equations 35,56, and 44 ... 

Two methodologies were used to determine the activation energies in the glassy region, since the apparent activation energy for viscoelastic relaxation is formally ealculated by the following equation ... 

Observing that can also be determined, independent of a model, by taking the first derivative of a plot of the ln(ay ) versus l/r, a C2-cubic spline was fit to the data to obtain the variation of the apparent activation energies for viscoelastic relaxations with temperature. 

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See also in sourсe #XX -- [ ]

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