Relaxation of Spherical Micellar Systems of Styrene−Isoprene Diblock Copolymers. 1. Linear Viscoelastic and Dielectric Behavior

Abstract

Linear viscoelastic and dielectric relaxation behavior was examined for blends of styrene−isoprene (SI) diblock copolymers in a nonentangling homopolyisoprene (hI) matrix. The copolymers formed spherical micelles with S cores and I corona. The I blocks had type-A dipoles, and their global motion induced dielectric relaxation. The micelles exhibited fast and slow relaxation processes for both dielectric loss e‘‘ and viscoelastic moduli G*. For the fast process, a nearly universal relationship was found for reduced moduli Gr* = [MbI/cbIRT]G*SI and reduced frequencies ωτ*, where G*SI was the contribution of the SI micelles to G*, MbI and cbI were the molecular weight and concentration for the I block, and τ* was a relaxation time that increased exponentially with cbI for large cbI. Similar behavior was found also for e‘‘SI (SI contribution to e‘‘). These features were qualitatively the same as those for the relaxation of star chains, indicating that the fast process corresponded to starlike relaxation of ind...