Guidelines for checking performance and verifying accuracy of rotational rheometers: viscosity measurements in steady and oscillatory shear (IUPAC Technical Report)

Abstract

Abstract:The paper addresses techniques for checking the performance of rotational rheometers with coneplate, plate-plate, or concentric cylinder geometry. We focus on the determination of the viscosity as a function of the shear rate and of the magnitude of the complex viscosity as a function of the angular frequency. After summarizing the relevant definitions and test modes, we show examples of measurements in the linear viscoelastic range, and applications of the Cox-Merz relationship. Sources of reference fluids with defined viscosities are presented, and their use in tests for verification of accuracy is demonstrated. Relevant issues, predominantly for Newtonian reference liquids, are the exploration of measurement limits, related either to the shear rate range or to reliably accessible viscosity levels. Viscoelastic reference samples are also discussed. Prerequisites for sample preparation and loading are addressed. In particular, we present recommendations based on experience from various laboratories. Finally, we discuss the problem of temperature calibration, presenting techniques that allow the determination of the true sample temperature for a given set temperature of the rheometer. This paper summarizes contributions from various industrial and academic laboratories.

Contact-free determination of viscosity in multiple parallel samples

“…Absolute measuring systems include rotation and oscillation rheometers that use concentric cylinders, plate-plate or cone-plate systems to determine the flow behaviour of Newtonian and non-Newtonian fluids. Concentric cylinders consist of a measuring cup and a bob with a narrow gap, and can be defined as Couette type (outer part rotates) or Searly type (inner part rotates) 18 . Typically, concentric cylinders are used for low-viscosity or particulate systems and are difficult to clean 19,27 .…”

“…These advanced rotation and oscillation rheometers are more expensive and more sensitive than the simpler pressure-driven and drag flow viscometers because they contain components such as air bearings. They also have limitations such as inaccurate measurement of the true sample radius 18,29 , hydrodynamic instability 30,31 , low torque limit 32,33 and wall slip behaviour 34 .…”

Assessment of Piezoelectric Sensors for the Acquisition of Steady Melt Pressures in Polymer Extrusion

“…The pressure mismatch produces a vertical shift between the flow curves, the differences between the measured viscosities being larger at smaller shear rates than at larger shear rates. Nonetheless, the discrepancy between the measured viscosities remains in the range 5.6% to 10% (see also Table 2), which can be assumed as acceptable if one considers the 10% experimental error usually reported for rotational rheometry [21] and recently confirmed with Newtonian viscosity standards [22] and with a low density polyethylene studied at 150 °C [14]. The operability window of the piezoelectric transducers is now examined by testing materials showing different levels of viscoelasticity and comparing the resulting flow curves with those measured using conventional transducers.…”

Development of magnetoactive elastomers for sealing eye retina detachments

“…Rheological properties of MAEs were studied using a Rheometer (Anton Paar, model Physica MCR 302), with a measuring “plate‐plate” unit and a magnetic cell. Measurements of the dynamic modulus of MAE samples were performed in the dynamic mode of forced torsion oscillations with a controlled torque varying according to a harmonic sinusoidal law . Disc‐shaped samples with a diameter of 20 mm and a height of approximately 1 mm were secured between a stationary lower plate and an upper plate connected to a rotor subject to forced torsion oscillations.…”