Experimental evidence of co-existence for equilibrium and nonequilibrium in two-glass-transition miscible mixtures
Two glass-transitions have been observed in some miscible molecular mixtures with notable difference in geometry or chemistry of constituents. Explanation of the phenomena has been puzzling with diverse structural models. Here, we presented detailed studies of the two glass-transition mixtures composed of tripropyl phosphate (TPP) and polystyrene (PS) by using calorimetric and dielectric measurements. We found that ageing between the two transitions always generates endothermic peaks at temperatures ~ 4 K higher than the ageing temperatures and, subsequent thermal cycles around the peaks can remove the ageing effect and restore the systems, confirming co-existence of nonequilibrium and equilibrium states in the regions. We also found that the broad glass transition thermogram is associated with highly stretched relaxation dynamics. The results allow us to draw a conclusion of continuous mobility gradient spanning the two TPP-PS glass-transitions, rather than complete phase separation.