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Complex fluids containing micelles, proteins, polymers and inorganic nanoparticles are often processed and used in high shear environments that can lead to structural changes at the nanoscale. Here, capillary rheometry is combined with small-angle neutron scattering (SANS) to simultaneously measure the viscosity and nanostructure of model complex fluids at industrially-relevant high shear rates. Capillary RheoSANS (CRSANS) uses pressure-driven flow through a long, flexible, silica capillary to generate wall shear rates up to 10 6 s -1 and measure pressure drops up to 500 bar. Sample volumes as small as 2 mL are required, which allow for measurement of supply-limited biological and deuterated materials. The device design, rheology and scattering methodologies, and broad sample capabilities are demonstrated by measuring a variety of model systems including silica nanoparticles, NIST monoclonal antibodies, and surfactant worm-like micelles. For a shear-thinning suspension of worm-like micelles, CRSANS measurements are in good agreement with traditional RheoSANS measurements. Collectively, these techniques provide insight into relationships between nanostructure and steady-shear viscosity over eight orders of magnitude in shear rate. Overall, CRSANS expands the capabilities of traditional RheoSANS instruments toward higher shear rates, enabling in situ structural measurements of soft materials at shear rates relevant to extrusion, coating, lubrication, and spraying applications.

In situ measurement of fluid structure during flow, e.g., by neutron scattering, is key to understanding the relationship between structure and rheology. For some applications, structures at high shear rates previously unreachable are of particular interest. Here, we report development of a flow cell slit rheometer for neutron scattering (μRheoSANS). The devices were used to measure the structure of a semi-dilute surfactant solution of worm-like micelles during flow. Analysis of the rheometry and scattering data allows isolation of the scattering signal from the high-shear, near-wall region of the flow cell. The reported results agree with those from the existing Couette-based RheoSANS instrument. The worm-like micelles exhibit an alignment transition at Weissenberg number (Wi) ≈ 1, coinciding with the onset of shear thinning. This transition is followed by a peak in micelle alignment at a higher shear rate, after which the degree of alignment decreases moderately. This technique can achieve higher shear rates than existing RheoSANS techniques, expanding the ability to study the structure of complex fluids at elevated shear rates.Using a slit rheometer for in situ neutron scattering, shown here are 2D SANS patterns and schematic velocity profiles for wormlike micelles undergoing pressure-driven flow through a rectangular capillary (left), the same system after isolating the scattering occurring in the near-wall high-shear region (center), and the same micellar fluid undergoing Couette flow at a shear rate equal to the wall shear rate in the shown pressure-driven flow. [ABSTRACT FROM AUTHOR]