Component Dynamics in Polymer/Polymer Blends: Role of Spatial Compositional Heterogeneity

The segmental relaxation times τA and τB of the A and B components, respectively, of an A/B polymer/polymer blend typically exhibit dissimilar temperature dependences and can differ by orders of magnitude, thereby manifesting the influence of spatial compositional heterogeneity. We show that for weakly miscible A/B blends the relaxations of the faster A component occur via separate and distinct mechanisms. In the melt state, τA increases in a nonlinear manner as temperature T decreases toward blend glass transition temperature Tg(blend) (or toward the local effective glass transition temperature of its component Tg(A)); this is the typical α relaxation process. For temperatures below the transition, 1/τA exhibits an Arrhenius temperature dependence; this is identified as the α′ process. A third relaxation process, a so-called α0 process, also occurs in the melt state; it is slower than the α process and exhibits a significantly stronger dependence on temperature. Each relaxation process, characterized by a different dependence on temperature, occurs via a different mechanism and associated local composition. This behavior, the existence of the α0 and α′ relaxations that accompany the α relaxations, would occur in miscible and weakly miscible blends whose component Tgs differ significantly.