Regensburg 2007 – scientific programme

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DY: Fachverband Dynamik und Statistische Physik

DY 26: Ferrofluids / Liquid crystals

DY 26.8: Talk

Thursday, March 29, 2007, 12:15–12:30, H3

Rheological investigations of ferrofluids with a shear stress controlled rheometer — •Hamid Shahnazian and Stefan Odenbach — Lehrstuhl für Magnetofluiddynamik, Technische Universität Dresden, 01062 Dresden

Ferrofluids, suspensions of magnetic nanoparticles with a mean diameter of about 10 nm in appropriate carrier liquids, show normal liquid behaviour coupled with superparamagnetic properties. This enables to influence significantly their flow behaviour by moderate magnetic field strengths, giving rise to numerous technical and biomedical applications. One of the major attributes of ferrofluids is the change of viscosity (magnetoviscous effect) and the appearance of viscoelastic effects caused by applied magnetic fields. Different theoretical approaches have been developed to explain these effects. The predictions of these models differ in a point, which comes into a question of an appearance and field dependence of yield stress in ferrofluids. For the investigations concerning yield stress a shear stress controlled rheometer for magnetic fluids has been designed. For different kind of ferrofluids, a dependence of the yield stress on magnetic field strength is observed. In order to get information on the size of the structures, formed by the particles under magnetic field influence, and its dependence on field strength as well as on interparticle interaction, variation of geometry - cone/plate or plate/plate - and distance of the walls in plate/plate geometry of the shear cell have been used.