Shear Induced Phase Boundary Shift in the Critical and Off-Critical Regions for a Polybutadiene/Polyisoprene Blend

Abstract

The rheology of near- and off-critical elastomeric blends of polybutadiene (PB)/ low vinyl content polyisoprene (LPI) has been studied as a function of temperature, heating rate, and shear frequency. Depending on the composition, near or far away from the critical point, blends showed different behaviors in several aspects: temperature ramp curves, shift of the apparent binodal and spinodal points under oscillatory shear at the given frequency and strain amplitude. The composition dependent rheological responses are interpreted by the differences in the amplitude of the critical fluctuation near the phase boundary and in the shear induced mixing mechanisms between near- and off-critical blends. For near-critical blends, the critical fluctuation is large enough to induce a considerable extra stress when the blend is still in the miscible state. As a result, a heating rate independent upturn of G′ can be observed and the apparent spinodal point can be greatly shifted through the strong suppression of the la...