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Hamid Shahnazian, Stefan Odenbach
New driving unit for the direct measurement of yield stress with a stress controlled rheometer
Appl. Rheol. 18:5 (2008) 54974 (7 pages)
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Investigations of rheological properties of ferrofluids have shown strong changes of the viscosity in magnetic fluids
with an applied magnetic field. The change of the viscosity . the magnetoviscous effect . can theoretically be described
with chain and structure formation under the influence of a magnetic field. Moreover, the formation of these structures
leads to the appearance of viscoelastic effects or other non-Newtonian features like yield stress in ferrofluids
with an applied magnetic field. With a shear rate controlled rheometer . as it as been used in former experiments .
the yield stress could not be investigated directly. Therefore the results concerning a field dependent yield stress based
on an extrapolation of shear controlled measurements. For the direct investigations of the yield stress, a dedicated
stress controlled rheometer is required, allowing direct investigations of the magnitude and field dependence of this
effect. In this work the design of the stress controlled rheometer with its main parameters has been described in detail.
The rheological investigations with differently composed fluids show that the stress controlled rheometer enables
direct measurements of even small yield stresses in ferrofluids as well as large effects like they are found in magnetorheological
fluids (MRF).
► Cite this publication as follows:
Shahnazian H, Odenbach S: New driving unit for the direct measurement of yield stress with a stress controlled rheometer, Appl. Rheol. 18 (2008) 54974.
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