Vane rheometry of viscoelastic liquids and yield stress fluids

An inter-laboratory comparison was performed to set a baseline for how the properties of difficult materials vary based on location and measurement tool. These tests focused on rheology of a Newtonian fluid, a viscous silicone oil, and two colloidal gels with yield stress behavior: a commercially available milk-based cream and an aging aluminum oxide hydroxide gel. Rheological data were collected on these materials using an array of rheometric test geometries including a cone and plate, parallel plates, a cup and bob, a 4-arm vane, and 12- and 24-arm vanes having fractal cross section that were fabricated independently by each lab and for which accurate torque and rotation conversion factors have been established. Characterization by the 3D-printed fractal vanes agree between the two laboratories and agree with reference data obtained with cone-and-plate, parallel-plate, and cup-and-bob measurement tools. The viscous oil exhibited predominantly Newtonian behavior in shear while weak viscoelastic effects emerged at high frequency and can be accurately described by a fractional Maxwell model. The colloidal gels exhibited a more intricate thixo-elastoviscoplastic (TEVP) rheological behavior, including thixotropy, as well as distinct dynamic and static yield stresses. To explore the elastoviscoplastic character of these systems, we show how the fractal vane geometry can be readily utilized with such materials to measure creep and partial elastic recoil without concern about slip or shear banding.