Electric Field Assembly of Colloidal Superstructures.

The assembly of materials from building blocks has been in the core of a wide range of applications from catalysis to photonics and electronics. External electric fields enable the interactions between building blocks to be controlled via induced dipoles. Dipolar interactions were used so far to obtain one-dimensional chains or three-dimensional non-close-packed lattices. However, complex colloidal assemblies and clusters of simple spherical particles are rare. Here we demonstrate a novel self-assembly approach enabling the formation of regular axially symmetric clusters, an array of colloidal assemblies as per design of posts, and hierarchical complex assemblies by using posts and dipolar interactions or combining them. Regulating the polarization of the particles from positive to negative allows us to control the interparticle interactions from attractive to repulsive at the poles or equator of the particles. Therefore, such particle-particle interactions enable switching between Saturn ring-like and candle-flame-like axially symmetric assemblies, which could potentially be exploited for display applications.