Structural Dynamics of Polymer and Surfactant Solutions in Planar Extensional Flow Using In Situ X-ray Scattering

The non-Newtonian properties of polymers and other complex fluids stem from molecular- and meso-scale structural changes induced by flow. In situ scattering is a powerful tool to interrogate fluid structure during flow, but usually has been limited to shearing flows. This proposal describes a research program centered on creation and application of novel x-ray scattering capabilities for studying mobile fluids in a planar extensional flow produced at the stagnation point of a cross-slot flow device. Prior efforts to apply x-ray and neutron scattering in this vein have been severely limited by design compromises in flow cell construction that result in kinematic inhomogeneity and spurious effects of parasitic shear gradients. Exploiting capabilities of the Advanced Photon Source, the design concept proposed here provides a marked improvement in the definition of the applied flow field. While the methods to be developed here will have broad applicability to many classes of complex fluids, two targets are proposed for initial study: structural dynamics of viscoelastic wormlike micelle solutions, and the deformation of flexible polymers in dilute solution.