The flow of molecularly well-characterized polymer liquids in a wavy channel will be investigated quantitatively and in considerable local detail. This model geometry provides a complexity of flow approaching that encountered in the commercial processing of polymer materials, and yet also allows the effects of non-Newtonian behavior on the stress and velocity fields to be determined by non-invasive optical techniques. An apparatus to accomplish this was developed and tested under a previous grant (CBT-88-19660). The use of nearly-monodisperse model polymers will now allow comparisons with the predictions of constitutive equations based on molecular theory. Researchers at Exxon Corporate Laboratories will participate in the work, supplying the model materials and collaborating in characterization, analysis and interpretation of results. Viscoelastic effects dominate the flow behavior of polymers in many commercial processing operations. Viscoelastic properties also depend strongly, and essentially universally, on the large scale molecular architecture (molecular weight, distribution, branching) of the polymer. Molecular theories can now successfully account for many of these architectural effects, but are still relatively untested, even for qualitative guidance, in the complex flow histories that typify a real processing situation. This research will supply such tests with model materials, allowing thereby a direct contact with the predictions of molecular theory. It will also provide a detailed body of information (the velocity and stress fields) for use in testing the computational methods of non-Newtonian fluid mechanics. The purposeful design of polymeric architecture (e.g., molecular weight distribution) for optimal processing behavior and for final product properties is a long-time goal throughout the polymer industry. Differences in behavior frequently correlate with differences in architecture, but molecular theories of polymer rheology are still untested in processing flow regimes. Moreover, detailed data for evaluating the computational methods of non- Newtonian fluid mechanics are very limited even for commercial polymers, where the architecture is uncertain and where molecular theories to account for the effects of molecular weight distribution are only now being developed. The wavy-wall study, utilizing model materials, offers a way to close some of these gaps in the connections between molecular architecture and the processing behavior of polymers.
