Münster 1999 – wissenschaftliches Programm

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SYFF: Symposium Ferrofluide

SYFF 1: Ferrofluide I

SYFF 1.1: Hauptvortrag

Donnerstag, 25. März 1999, 14:30–15:15, R1

Negative Viscosity in Magnetic Fluids: Mechanisms, Manifestations, and Connected Effects — •Mark I. Shliomis — Department of Mechanical Engineering, Ben-Gurion University of the Negev, P.O. Box 653, Beer-Sheva 84105, Israel

Ordinarily the viscosity of magnetic fluids (MFs) increases in applied magnetic field. This behavior was believed to be general, but recent theoretical analysis predicts and experimental investigations demonstrate that under appropriate conditions with a time-varying field, the viscosity of MFs exhibits a substantial reduction, that is, a negative viscosity component. The theory predicts a tight connection between this Negative-Viscosity effect and the Vortico-Magnetic resonance of the off-axis (i.e., transversal to the oscillating field) component of MF magnetization. Both these phenomena represent themselves two sides of a curious mechanism of the energy conversion in MFs. Depending on the ratio r of the field frequency to the fluid vorticity, magnetic nanoparticles suspended in a liquid carrier behave as either nanomotors or nanogenerators. A crossover takes place at r=1.

A direct and vivid experimental evidence of the Negative-Viscosity effect through its relation with the Vortico-Magnetic resonance will be presented.