Simultaneous slit rheometry and in situ neutron scattering

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.