Comparison of Dynamic Mechanical and Dielectric Results

The relaxation map of PMMA obtained from and s is shown in Fig. 111. It shows a good agreement between the two types of investigations, in agreement with the fact that the same motional groups are involved in the response of both techniques. 

Furthermore, the activation energies (83 =b 5 kj mol from mechanical analysis and 82 ib 2 kJ mol from dielectric relaxation) as well as the activation entropies (51 =b 3 J mol from mechanical analysis and 58 d= 33 J mol from dielectric relaxation) are identical, confirming that the processes are the same. 

the mechanical loss generated at the a transition is much larger than the dielectric one. 

Another interesting feature deals with the crossover region between the 

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Non-linear mechanical properties were observed for rubber eomposites and referred to as the Payne effect. The Payne effeet was interpreted as due to filler agglomeration where the filler clusters formed eontained adsorbed rubber. The occluded rubber molecules within filler elusters eould not eontribute to overall elastic properties. The composites behaved similarly to rubber composites with higher filler loading. Uniform and stable filler dispersion is required for rubber composites to exhibit linear viscoelastic behaviour. Payne performed dielectric measurements on SBR vulcanizates containing silica or carbon black. The dielectric data were used to construct time-temperature superposition master curves. The reference temperature increased with crosslinking but not significantly with filler. Comparison of dynamic mechanical and dielectric results for the SBR blended with NR was made and interpreted. ... 

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