(80b) Characterizing Structure-Rheology Relationships in Complex Fluids at High Shear Rates Using Simultaneous Slit or Capillary Rheology and Neutron Scattering

Neutron scattering gives unparalleled insight into the nanoscale structure in a wide variety of complex fluids and soft materials. As a probe, the neutron is only weakly interacting with many materials and sensitive to isotopic differences. These advantages allow for studying single components in multicomponent mixtures through careful contrast matching via isotopic substitution and the use of complex sample environments without excessive loss of signal due. For these reasons and more, neutron scattering has been used in parallel with a variety of flow cells and rheometers for decades. Modern rheoSANS instruments tend to be cup and bob instruments that simultaneously measure rheology and structure at shear rates up to a few thousand reciprocal seconds. This has enabled a wide array of materials to be studied including particle suspensions, wormlike micelles, pluronic solutions and gels to name a few. However, in many applications, soft materials experience complicated flow profiles or very high shear rates. In order to address the need for characterizing structure of fluids under industrially relevant processing and application conditions, our team has been working toward developing measurements to enable the simultaneous characterization of the rheology and structure of complex fluids at relatively high strain rates and in more complex flow environments. To date, we have developed a prototype slit rheometer capable of simultaneously measuring structure and rheology of relatively low viscosity or shear thinning fluids (η_∞ < 5 mPa∙s) at shear rates up to 100,000 s^-1 and a capillary rheoSANS instrument capable of simultaneously measuring structure and rheology at rates in excess of 10⁶ s^-1. In combination with standard Couette rheoscattering measurements, we have used this suite of measurement tools to investigate the relationship between structure and rheology in variety of complex fluids including suspensions, protein and polymer solutions, and wormlike micelles. In this talk we will highlight our recent measurements, with emphasis on characterizing the structural changes observed in wormlike micelles at very high shear rates. Recently, we have focused on controlling the morphology of a model system of wormlike micelles by adjusting the salt/surfactant ratio and surfactant concentration with the goal of tuning the micelle length without altering the persistence length, enabling the creation of a library of micelles spanning the rod like to wormlike regimes. The structure and rheology of these micelles systems are characterized at shear rates from 0.01 to 10⁶ s^-1 using a combination of rheoSANS and capillary rheoSANS.