Rheo-PIV of Aerosil® R816/polypropylene glycol suspensions

• Rheo-PIV and measurement of rheometric properties simultaneously.
• Image deformation technique to improve Rheo-PIV.
• Azimuthal velocity profiles analysis in shear-thickening/shear-thinning regions.
• Change in the trend of the azimuthal velocity profile depending on the rheological region.

In this study we adapt a conventional rotational rheometer to perform PIV measurements on wide gap Couette flow. We measure the radial profile of the azimuthal velocity and the rheometric properties simultaneously. We use image deformation to convert the images from cylindrical coordinates to a rectangular frame, thus improving the PIV algorithm performance. This technique is validated with the Newtonian liquid phase of the rheological suspensions, showing an excellent agreement with the theoretical velocity profile. We also characterize the rheological properties of Aerosil® R816 Polypropylene Glycol suspensions, which show a shear-thickening behavior between two shear-thinning regions. The relation between the viscosity and the shear rate is computed in the whole radial domain between the inner and the outer cylinder. These Rheo-PIV measurements allow us to distinguish the onset of shear thickening and jamming, the former one being connected to a smooth change in the measured shear rate, whilst the latter corresponds to a sudden change in the measured shear stress value.