Chapter 8. New Insights from Rheo-small-angle Neutron Scattering

Abstract

Rheo-small angle neutron scattering (rheo-SANS) methods combine microstructural SANS measurements with an applied deformation field in order to measure flow-induced structures in complex fluids. Such methods enable a robust characterization of the microstructure and flow properties of surfactant wormlike micelle (WLM) solutions. The development of new sample environments now enables the flow-induced microstructure to be measured in the three planes of shear: the flow–vorticity (1–3), flow–gradient (1–2), and gradient–vorticity (2–3) planes. Advances in neutron collection and data analysis have improved the temporal resolution of time-dependent responses, significantly reducing the time required to perform such measurements. Theoretical advances in constitutive modelling and the stress-SANS rule now permit the development and testing of structure–property relationships. Such methodologies have allowed flow instabilities, such as shear and vorticity banding, and shear-induced structural transitions to be identified in WLM solutions. Additional sample environments have enabled the study of WLMs under extensional and Poiseuille flows, in addition to flows in microfluidic devices.