Self-assembly of particles into 2D lattices with adaptable spacing

It was recently shown in [1-3] that spherical particles floating on a fluid-fluid interface can be self-assembled, and the lattice between them can be controlled, using an electric field. The technique works for a broad range of fluids and particles, including electrically neutral (i.e., uncharged) particles and small particles (micro- and nano-sized particles). In this paper we show that the technique also works for rod-like and cubical particles floating on fluid-fluid interfaces. The method consists of sprinkling particles at a liquid interface and applying an electric field normal to the interface, thus resulting in a combination of hydrodynamic (capillary) and electrostatic forces acting on the particles. It is shown that the relative orientation of two rod-like particles can be controlled by applying an electric field normal to the interface. The lattice spacing of the self-assembled monolayer of rods can be increased by increasing the electric field strength. Furthermore, experiments show that there is a tendency for the rods to align so that they are parallel to each other. The alignment however is not complete. Similarly, the spacing between two cubes, as well as the spacing of a monolayer of cubes, can be adjusted by controlling the electric field strength.