Measurement of viscoelastic properties of a liquid using a rotating body of a general shape subjected to oscillatory shear

We propose a systematic approach for measuring linear and non-linear viscoelastic properties of a liquid by the oscillatory motion of an immersed rotating body in a vessel. The shape of a rotating object is general and we tested four different types of impellers in the present work: a disk, an anchor, and two different flat bladed turbines. The effective shear stress was properly scaled with a torque through the expression of complex viscosity and the strain magnitude was scaled by the deflection angle with an effective shear rate coefficient (the Metzner-Otto constant). Three different concentrations of aqueous polyethylene oxide (PEO) solutions were tested and linear viscoelastic responses of storage and loss moduli were measured as a function of the oscillation frequency. In spite of the presence of non-rheometric and highly non-uniform flow field, comparison with the data from the conventional cone-and-plate and parallel-plate fixtures of a rheometer shows remarkably accurate measurement with at most 7% deviation within the frequency range from 0.01 [rad/s] to 100 [rad/s] for all the impeller geometries, except for the pitched bladed turbine. In addition, we show that this method can be applied to large amplitude oscillatory shear experiments for non-linear viscoelastic properties. The proposed method provides a versatile measurement for viscoelasticity, eliminating complicated issues in the conventional rheometry such as the wall slip, free surface evaporation/solidification and the edge fracture without a significant loss of accuracy. Furthermore, the method may facilitate the in-situ measurement of viscoelastic properties of a fluid within an industrial reactor/agitator as a tool for in-situ/on-line monitoring of microstructures.