Magnetic Cheerios Patterns

D04Bz50gauss_113The “Cheerios effect” [1] is known as the capillary attraction between identical floating objects at some liquid-air interface, similarly to the case of the famous cereals in a bowl. The capillary attraction is a major ingredient in mesoscale self-assembly.

In a recent paper [2], we have proposed to combine capillary attraction and magnetic repulsion by applying an external field to soft ferromagnetic particles. The competition between attraction and repulsion leads to equilibrium distances between particles. In the case of oscillating magnetic field, locomotion has been obtained [3].

In a new paper [4], we investigated experimentally the case of a large number of particles. Contrary to what we expected, the self-assembled structure does not show crystal features but many defects are created due to the local curvature of the liquid-air interface. This is analyzed in this paper. Although crystals were not observed, beautiful patterns (as shown in the picture) were generated. 

[1]  D.Vella and  L.Mahadevan, Am. J. Phys. 73, 817 (2005)
[2] N.Vandewalle et al, Phys. Rev. E 85, 041402 (2012) – PDF
[3] G.Lumay, N.Obara, F.Weyer, N.Vandewalle, Soft Matter 9, 2420 (2013) – PDF
[4] N.Vandewalle, N.Obara and G.Lumay, EPJE 36, 127 (2013) – PDF

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About nicovdw

Professor in Physics
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