Molecular dynamic in binary mixtures and polymer blends with large difference in glass transition temperatures of the two components: A critical review

The dynamics in highly asymmetric mixtures with large difference in T-g of the two components are complex. At low values of the lower-T-g(2) component only the alpha 1-relaxation and its T-g(alpha 1) were found together with a fast relaxation. Three different interpretations of the fast relaxation were given. The first one interpreted the fast relaxation as the JG beta-relaxation, and the alpha 2-relaxation is present but not resolved. The second one interpreted it as localized and noncooperative alpha '-relaxation of the low-Tg2 component totally confined by the frozen high-T-g(1) component. The third one interpreted it also as the confined alpha 2-relaxation, but it is liquid-like and cooperative. We review exhaustively the experimental data of many highly asymmetric mixtures and polymer blends to show unequivocally that the observed fast relaxation is the JG beta-relaxation. Notwithstanding, the confined-butcooperative alpha 2-relaxation exists, albeit not resolved. Experimental data are exclusively considered and objectively utilized to arrive at the conclusions.

Automated summary

In highly asymmetric mixtures with large differences in T-g between components, the dynamics are complex and multiple interpretations of fast relaxations exist. Experimental data demonstrate the presence of JG beta-relaxation, with the confined-but-cooperative alpha 2-relaxation also playing a role.