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DY: Dynamik und Statistische Physik
DY 22: Ferrofluide II / Flüssigkristalle
DY 22.1: Vortrag
Dienstag, 27. März 2001, 11:45–12:00, S 5.5
Measurements of the rotational viscosity and the transverse relaxation time of ferrofluids — •Jan Peter EMBS1,2, Hanns Walter Müller3, Manfred Lücke1, and Klaus Knorr2 — 1Theoretische Physik, Universität des Saarlandes, Im Stadtwald, 66123 Saarbrücken — 2Technische Physik, Universität des Saarlandes, Im Stadtwald, 66123 Saarbrücken — 3Max-Planck-Institut für Polymerforschung, Ackermannweg 10, 55128 Mainz
In order to measure both, the rotational viscosity and the transverse relaxation time of ferrofluids, we designed a torsional pendulum of a high quality factor Q (Q about 1200). By filling the cylindrical fluid-container with plastic straws we suppress any disturbing shear and guarantee a pure solid-body rotation of the sample under investigation. In an external magnetic field H0 perpendicular to the axis of the rotating ferrofluid, a non-equlibrium situation is created, in which the magnetization is forced out of the direction of the applied magnetic field. The resulting dissipative torque leads to a field-dependent damping of the pendulum. We measure both, the amplitude and the phase-lag as function of the applied field strength; by fitting the resonance curves we obtain directly the rotational viscosity and the transverse relaxation time τ⊥(H) of the fluid. In my talk new experimental results are presented and interpreted in two different theoretical approaches.