Dresden 2009 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 20: Focus: Magnetic Soft Matter II

CPP 20.1: Hauptvortrag

Mittwoch, 25. März 2009, 09:30–10:00, ZEU 222

Truncated patterning in the normal field instability — •Andreas Boudouvis — School of Chemical Engineering, National Technical University of Athens, Athens 15780, Greece

The normal field instability sets in a pool of ferrofluid when the strength of a uniform magnetic field, applied in a direction normal to the horizontal free surface of the pool, exceeds a threshold.

Most studied in laterally unbounded pools, the instability gives way to spontaneously formed static patterns of spikes exhibiting striking spatial symmetry, usually hexagonal and rarely square [1, 2].

The finiteness of a pool introduces "imperfections", namely lateral pattern truncation along with side-wall wetting [3]. Of concern here is the normal field instability and the accompanying pattern formation in round containers of moderate diameter. Bifurcation diagrams of truncated patterns of two, three and four spikes are computed by solving the equations of the 3-D capillary magnetohydrostatics with the Galerkin/finite element method. The theoretical predictions, which are in good agreement with experimental measurements, reveal the structure of the solution space, namely the connectivity, the multiplicity and the stability of the truncated patterns, in the studied parameter "window", defined by varying applied field strength and container diameter.

[1] Cowley M D & Rosensweig R E 1967 J. Fluid Mech. 30, 671. [2] Gollwitzer C, Matthies G, Richter R, Rehberg I & Tobiska L 2007 J. Fluid Mech. 571, 455. [3] Boudouvis A G, Puchalla J L & Scriven L E 1988 J. Colloid Interface Sci. 124, 677.