Sabrina Disch

Title: Orientation Behavior of Anisometric Magnetic Nanoparticles in Dynamic Magnetic Fields

Abstract: Magnetic nanoparticles find widespread attention with numerous applications, e.g. nanomedicine [1], smart fluids [2], and active matter with self-propelling particles [3] that can be manipulated with static and dynamic magnetic fields. Hematite nanospindles are particularly fascinating as they orient with their principal axis perpendicular to an applied magnetic field in contrast to typical ferromagnetic compass needles. In addition, the anisometric shape gives rise to two distinct motions around the long and short axis that directly affect their response to magnetic fields, as we can monitor closely with small-angle X-ray and neutron scattering (SAXS/SANS) techniques.

In this talk, I will show how different collective rotation modes of hematite nanospindles can be separated using a rotating magnetic field of varying frequency and tracing the particle motion with time-resolved SAXS [4]. I will demonstrate that nanospindles allow to probe the local viscosity even in opaque complex fluids [5] when using neutrons. Time-resolved SANS under an oscillating field gives unambiguous access to the characteristic frequency of rotational diffusion. Finally, the combination of a static magnetic field and shear flow leads to different, competing reorientation effects that we disentangled using a dedicated SANS setup enabling microscopic studies of magnetoviscous effects [6].

[1] Q. A. Pankhurst, J. Connolly, S. K. Johnson, J. Dobson, J. Phys. D: Appl. Phys. 36 (2003) R167.

[2] J. de Vicente, D. J. Klingenberg, R. Hidalgo-Alvarez, Soft Matter 7 (2011), 3701.

[3] G. Z. Lum, Z. Ye, X. Dong, H. Marvi, O. Erin, W. Hu, M. Sitti, PNAS 113 (2016), E6007–E6015.

[4] D. Honecker, P. Bender, Y. Falke, D. Dresen, M. Kundt, A. M. Schmidt, A. Tschöpe, M. Sztucki, M. Burghammer, S. Disch, Controlling the Rotation Modes of Hematite Nanospindles by Dynamic Magnetic Fields, preprint (2022). doi: 10.26434/chemrxiv-2022-c0hh4

[5] C. Glinka, M. Bleuel, P. Tsai, D. Zákutná, D. Honecker, D. Dresen, F. Mees, S. Disch, J. Appl. Cryst. 53 (2020), 598 – 604.

[6] D. Zákutná, K. Graef, D. Dresen, L. Porcar, D. Honecker, S. Disch, Colloid Polym Sci 299 (2021), 281 – 288.