A New Rheo-Light-Scattering Instrument for the Study of the Phase Behavior of Polymer Blends Under Simple-Shear Flow
A rheo‐light‐scattering instrument for investigating the influence of shear on the phase behavior of polymer blends was constructed from a commercial parallel‐plate rheometer. Laser light scattering from the sample plane formed by the flow and vorticity directions was projected on a screen, and a combination of a camera lens and a charge‐coupled device detector was used to record the scattering pattern. The rheometer, which can generate angular velocities of up to 100 rad/s and measure torque and normal forces up to 9.8×103 N m and 9.8×105 N, respectively, is suitable for studying polymer melts at stresses up to 9.1 kPa. The maximum accessible q range was from 5.72×10-4 to 7.11×10-3 nm-1 (3°–42° scattering angle and a laser wavelength of λ=632.8 nm). The performance of the light‐scattering instrumentation and the accuracy of the correction algorithms were tested with a Ronchi ruling diffraction grating and a colloid of monodisperse polystyrene spheres. Example rheo‐light‐scattering measurements were made with a 50/50 blend of polystyrene and polyisobutylene oligomers and a 40/60 blend of polybutadiene and polyisoprene. All components had narrow molecular weight distributions. The first blend exhibits an upper critical solution temperature while the second blend shows a lower critical solution temperature.