Cylindrical intermediates in a shearinduced lamellar-to-vesicle transition J. Zipfel, F. Nettesheim, P. Lindner et al.Rheo-SAXS investigation of shear-thinning behaviour of very anisometric repulsive disc-likeclay suspensions A M Philippe, C Baravian, M Imperor-Clerc et al. Abstract. We discuss the application of in-situ rheological small angle X-ray scattering experiments to the study of complex fluids under shear, implemented using custom Couette cylinder rheometers mounted on the SWING beamline of the SOLEIL Synchrotron. We discuss several applications of this technique to the study of phase transitions in nanoparticle doped liquid crystals and shear alignment of clay suspensions. The concurrent capture of rheological and scattering data provides vital information that relates macroscopic properties such as viscosity to the microstructure of the fluid. IntroductionThe study of complex fluids and of their rheological properties is an active area of research with a wide range of applications.1 The bulk macroscopic properties of complex fluids, such as rheological properties such as shear viscosity, for example, will often depend on the structure of the fluid on a microscopic level. Thus it is often convenient to combine various techniques in order to study macroscopic and microscopic properties at the same time. Investigations using small angle scattering techniques (SAS) (light, neutrons, X-rays) can be performed on such fluids directly under flow; this allows the simultaneous recording of rheological quantities (such as flow-curves and viscosity profiles) and structural information. In the case of strongly anisotropic fluids, small angle X-ray or neutron scattering (SAXS/SANS) experiments are particularly well suited to following orientation phenomena of structured fluids under flow. Using new rheological small-angle (Rheo-SAXS) instruments developed at the SWING SAXS beamline of the SOLEIL synchrotron, we present some examples of results demonstrating in detail the behaviour under shear of doped surfactant lamellar phases and colloidal clay suspensions.