Structural a-Relaxation Dynamic Structure Factor

The dynamic process driving the decay of the interchain correlations in glassforming polymers is the structural a-relaxation. The direct microscopic obser- 

/Qj ax( ) is a generalized Debye-Waller factor giving account for the decay of the correlations at faster times. In the framework of the MCT it is also called non-ergodicity factor. The characteristic timescale r (T) is the structural relaxation time and (3 is the stretching parameter (0 jS l). 

The scaling the functional shape hardly depends on temperature. Curves corresponding to different temperatures superimpose in a single master curve when they are represented against a reduced time variable that includes a T-dependent shift factor. 

These two features are demonstrated in Fig. 4.3 for 1,4-polybutadiene (PB), in Fig. 4.4 for polyisobutylene (PIB) and atactic polypropylene (aPP), in Fig. 4.5 for polyurethane (PU) and poly(vinyl chloride) (PVC) and in Fig. 4.6 for poly(vinyl ethylene) (1,2-polybutadiene, PVE) (see Table 1.1 for microstructure). In each case 5pair(Qmax 0/Spair(Qmax 0) is Very well described by the KWW laws. 

At this point the question arises whether the feature usually termed as universality is also fulfilled do the timescales deduced from the investigation of different correlators in the a-relaxation regime show the same temperature 

---