Colloidal electroconvection in a thin horizontal cell. I. Microscopic cooperative patterns at low voltage

Applying an electric field to an aqueous colloidal dispersion establishes a complex interplay of forces among the highly mobile simple ions, the more highly charged but less mobile colloidal spheres, and the surrounding water. This interplay can induce a wide variety of visually striking dynamical instabilities even when the applied field is constant. This paper reports on the highly organized patterns that emerge when electrohydrodynamic forces compete with gravity in thin layers of charge-stabilized colloidal spheres subjected to low voltages between parallel-plate electrodes. Depending on the conditions, these spheres can form levitating clusters with morphologies ranging from tumbling clouds to toroidal vortex rings and to writhing labyrinths.