What Length Scales Control the Dynamics of Miscible Polymer Blends?

Abstract

The segmental dynamics of miscible polymer blends have been the focus of much recent research since the two constituents typically appear to experience different average dynamic environments. It has been suggested that these results can be attributed to concentration fluctuations coupled to chain connectivity effects. However, the relative importance of these two factors in determining chain dynamics is unresolved. Here we assess the importance of concentration fluctuations and also the magnitude of self-concentrations experienced by a test segment by analyzing literature values of the mean segmental relaxation times of the components of several miscible polymer blends and a disordered tetrablock copolymer. The self-composition derived in this manner is used to estimate the cooperative length scale which controls segmental dynamics, a quantity for which no first principles theory exists. Using a Taylor series expansion, we show that concentration fluctuations can strongly affect the mean relaxation time o...