Efficacy assessments in ultrasonic spinning rheometry: Linear viscoelastic analysis on non-Newtonian fluids

We have progressively developed an ultrasonic spinning rheometry (USR) that has the potential to visualize complex details of rheology, such as time-dependence, coexistence of gel and sol, effective viscosity of multiphase fluids, and other particulars. This rheometry makes it possible to overcome the main issues in conventional rheometry, originating from nonideal velocity profiles in the complex fluids. The most notable advantage of USR is the ability to perform "local" rheological evaluations from only the velocity information for a short-time period by solving the equation of motion. This benefit is provided while avoiding noise augmentations by introducing a linear viscoelastic analysis in the frequency domain. Solving the equation of motion with a rheological model equation in the frequency domain, multiple rheological parameters are quantified by minimizing the cost function. In this paper, the analysis presented by USR is verified by comparative experiments using a rheometer with the typical geometry of parallel disks. As a complementary technique for conventional rheometers, the USR efficacies are shown through rheological assessments for Newtonian, shear-thinning, and thixotropic fluids. Additionally, USR can provide instantaneous flow curves O(1 s) that lead to understanding the rheology in complex fluids with time-dependency. (C) 2019 The Society of Rheology.