(141c) Understanding Structural Changes in Complex Fluids at High Shear Rates: Developing µrheosans

Industrial applications, such as lubrication, mixing, spraying and injection, involve the flow complex fluids at extreme deformation rates. Clogging, fluid degradation, and other processing challenges can arise in these extreme contexts and are often driven by structural changes in the fluid. As an example, there are concerns that high shear rate delivery of protein therapeutics via injection with a very small bore syringe needle could alter the protein structure and drive aggregation, leading to toxic and potentially fatal health effects. For shear rates <10⁴ s^-1, the rheology and structure of a flowing fluid can be assessed using an established technique such as RheoSANS, RheoSAXS, confocal rheometry. High shear rate rheological characterization can be carried out using capillary and slit rheometers, but measuring the structure of complex fluids under these conditions is more challenging. It could potentially be achieved using light, x-ray, or neutron scattering; with neutron scattering providing particular advantages: neutrons probe the length scales of interest for many complex fluids, penetrate the materials used to construct capillary/slit rheometers, and provide the ability to adjust contrast to selectively probe the structure of particular components of the fluid. We have recently begun developing a series of microfluidic devices that will enable simultaneous rheological and structural characterization of complex fluids at high shear rates using small-angle neutron scattering (SANS). Prototype devices have achieved effective shear rates exceeding 10⁵ s^-1, and an apparatus can achieve shear rates >10⁶ s^-1 is under develpment. Additionally, a data analysis method has been developed to isolate scattering from the high-shear region located near the wall of the microfluidic channel, helping to better resolve shear rate dependent scattering. Here, we will discuss both the development of our new µRheoSANS apparatus and the data analysis approach in the context of initial measurements of a cetylpyridinium chloride-sodium salicylate wormlike micelle system.