Morphological Transition between Patterns Formed by Threads of Magnetic Beads

Abstract

Magnetic beads attract each other forming chains. We pushed such chains into an inclined Hele-Shaw cell and discovered that they spontaneously form self-similar patterns. Depending on the angle of inclination of the cell, two completely different situations emerge, namely, above the static friction angle the patterns resemble the stacking of a rope and below they look similar to a fortress from above. Moreover, locally the first pattern forms a square lattice, while the second pattern exhibits triangular symmetry. For both patterns the size distributions of enclosed areas follow power laws. We characterize the morphological transition between the two patterns experimentally and numerically and explain the change in polarization as a competition between friction-induced buckling and gravity.

Patterns formed by chains of magnetic beads

“…4. In fact, a transition to the flower-type pattern can be achieved by tilting the Hele-Shaw cell beyond the friction angle [18].…”

Collective dipole reorganization in magnetostructures

“…Conversely, in a triangular lattice, dipoles orients in chains that are parallel to their neighbors. These latter configurations are both the most compact and the more stable ones compared to the square lattice [14,15]. Please note that folding such 2D lattices leads to the formation of magnetotubes as shown in figure 1.…”

“…When creating magnetostructures, one realizes rapidly that the underlying dipole arrangement is as significant as the contact network between particles. This has been explained using equations ( 1) and ( 2) [9][10][11][12][13][14][15][16][17][18].…”