Self-aligning colloidal particles

Inducing the spontaneous association of microscopic building blocks into macroscopic structures has been a promising way to create new materials for a variety of useful applications. Controlling the positions and orientations of the microscopic building blocks is a critical issue in such processes. To date there has been no efficient or reliable process that enables such spontaneous assembly with controlled alignment of building blocks. Such fabrication processes typically require interactions between microscopic building blocks. For the successful alignment of any particles that we desire to self-assemble, a shape with unique physical and mathematical properties must be identified. Under the assumption that energy is reduced in proportion to area overlap, we present a geometrical shape which, when encountering a similar shape from any initial configuration, is forced into a single relative orientation maximizing the overlap. We have microfabricated colloidal structures called ``eccentroids'' that have such a shape. When a depletant solution is added to a solution of eccentroids, the eccentroids attract due to depletion interaction. We will show that the unique minimum of energy in the energy landscape drives the particles to self-assemble in a single controlled orientation.