Berlin 2008 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 2: DRG-DPG SYMPOSIUM Rheology II

CPP 2.5: Invited Talk

Monday, February 25, 2008, 15:30–16:00, C 130

Structure and dynamics of magnetorheological fluids — •Claus Gabriel and Hans Martin Laun — BASF AG, Ludwigshafen am Rhein, Germany

This presentation intends to give an overview of the rheological properties of magnetorheological fluids (MRF). MRF are used as force- or torque transmitting fluids in electronically controllable dampers and clutches.

Some fundamental structure-property relationships related to dynamic frequency sweeps will be discussed. The linear regime of deformation is the broader the higher the applied magnetic field is. In this regime MRF behave predominantly as elastic bodies and the dynamic moduli are essentially independent of the magnitude of the applied magnetic field. Outside the linear regime the internal structure of MRF breaks down. The MRF properties derived from dynamic experiments will be compared with those obtained from steady-shear experiments. Moreover, the dependence of rheological properties upon the composition of MRF will also be discussed.

An important precondition for a reliable determination of rheological properties of MRF is the homogeneity of the flux density in the shear gap. Depending on the type of MRF formulation a non-homogeneous flux density distribution may cause a significant segregation of the magnetisable particles within the MRF. An improved measurement design is proposed with which these segregation phenomena can be reduced to a minimum.