Energy for the glass transition, activation

As a function of MW Activation energy for the glass transition See Rets. 62,64... 

Similar wide dispersion of the activation energies within the glass transition has been obtained earlier for 4-arm star-like PS where chains were grafted to fullerene (Ceo) core [131],... 

The glass transition of PPS was studied by means of DSC, FTIR spectroscopy and energy dispersive X-ray diffraction. All of the techniques showed the alpha-transition of the polymer. The results of the different techniques were consistent if the onset temperature for the DSC experiments was taken as representative of the glass transition. The glass transition temperature was found to vary as a function of the heating rate. The activation energy of the glass transition process was calculated by means of a theoretical model. The results were discussed. 47 refs. 

Figure 6 shows the master curves for the PS films with M of 4.9k and 140k drawn by horizontal and vertical shifts of each curve shown in Fig. 5 at the reference temperatures of 267 and 333 K, respectively [26]. The master curves obtained from the dependence of lateral force on the scanning rate were very similar to the lateral force-temperature curves, as shown in Fig. 3. Hence, it seems plausible as a general concept that the scanning rate dependence of the lateral force exhibits a peak in a glass-rubber transition. Also, it is clear that the time-temperature superposition principle, which is characteristic of bulk viscoelastic materials [35], can be applied to the surface relaxation process as well. Assuming that Uj has a functional form of Arrhenius type [36, 37], the apparent activation energy for the aa-relaxati(Mi process, A//, is given by ...

The log-normal distribution of correlation times can be used to fit the relaxation data from concentrated polymer solutions. The data provide reasonable variations of the mean correlation times with concentration and temperature. Of the systems studied, PIPA-di was found to reorient much more rapidly than either PEA-di or PNBA-di. Relatively low energies of activation were found for PIPA-di in semi-dilute solution. These energies of activation increased with concentration and were similar for all three polymers until the highest concentration where the apparent energies of activation scaled with the glass transition temperature of the bulk polymers. 

Transition map of poly(vmyl alcohol) compiled using the DMA data presented in Figure 6.12. An activation energy for the a (motion in crystalline regions), (glass transition) and y (local mode relaxation) transitions can be calculated using the Arrhenius relation... 

It is worth noting that the temperature variation of characteristic times for the glass transition is not of Arrhenius type. It is specific to the glass transition phenomenon. Consequently, we cannot speak of an activation energy for this process, since it would be temperature dependent. 

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