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B. Fischer, J. Wagner, M. Schmitt, V. Trieu, Rolf Hempelmann

Dependence of Brownian Relaxation on the Volume Fraction and an External Field

Keywords: Magnetic Fluids, Brownian Relaxation

Co_xFe_3−xO₄ based ferrofluids were employed to study the dependence of the rotational diffusion on the concentration of magnetic particles and on a static external magnetic field. This influence is investigated in a frequency range 100 Hz ≤ f ≤ 700 kHz. With increasing volume fraction, the rotational motion is slowed down. The increase of the relaxation times can be described by an apparent increase of the effective viscosity originating from particle interactions. In a static external field, the rotation of large particles is trapped. Hence only the fraction of small particles is able to follow the ac-field and the magnetic relaxation appears to be faster. The critical particle size for a transition from free state into a trapped state depends on the strength of the static magnetic field.

Zeitschrift für Physikalische Chemie, Oldenbourg Wissenschaftsverlag

Print ISSN: 0942-9352
Volume: 220, 01/2006
Pages: 069 - 077

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