Dependence on sphere diameter

Figure 6: Labyrinthine patterns of 1.58  $\unit{\mu m}$ diameter silica spheres. $H = 200~\ensuremath{\unit{\mu m}}\xspace$ . $\phi \approx 50\%$ . (a) 4.0 V: labyrinthine convection rolls in the bulk. (b) 10 V: labyrinth of crystallites deposited on the upper electrode.

Under the same conditions that 3  $\unit{\mu m}$ diameter silica spheres form well-organized microscopic colloidal vortices, 1.58  $\unit{\mu m}$ diameter silica spheres form only tumbling clouds (6,7). Although these clouds show none of the internal organization of colloidal vortices, they nevertheless tend to organize themselves into labyrinthine patterns on substantially larger length scales, as can be seen in Fig. 6(a). Like the labyrinths formed by larger spheres, these patterns also coarsen with increasing bias. By about 10 V, however, the smaller lighter particles are driven onto the upper electrode, where they stick irreversibly. These adsorbed spheres typically are arranged into static labyrinthine domains with crystalline microstructure, an example of which appears in Fig. 6(b).