Effect of hydrodynamics on dynamics of phase separation in polystyrene/poly(vinyl methyl ether) blend

Poly styrene/poly (vinyl methyl ether) (PS/PVME) phase diagram was assessed by theological tools and by on-line microscopy observations both under quiescent and shear flow conditions. Shear flow was found to induce both mixing and demixing of the mixture depending on the amplitude of the imposed shear rate. Viscoelastic properties of PS/PVME blends were also measured under steady shear flow near the phase separation temperature. At lower shear rate, flow enhances concentration fluctuation and induces phase segregation. At high shear rate, flow suppresses fluctuations and the polymer mixture keeps its miscible state. Several theological signatures of phase transition were found. In steady shear flow, a secondary plateau in viscosity was observed when the temperature was close to T., whereas, at the start-up shear flow, transient shear stress showed a second overshoot after a few minutes of shearing. (c) 2005 Elsevier Ltd. All rights reserved.