Formation of “Colloidal Molecules” Induced By AC Electric Fields

Colloidal analogues of real molecules with controlled architecture are important building blocks for making mesocopic materials with exotic properties. Existing methods of making colloidal molecules mostly rely on particles that are anisotropic in terms of geometry or interfacial properties. However, those anisotropic particles themselves are challenging to make. In this talk, we demonstrate a simple and versatile method to build colloidal molecules based on isotropic particles that are commercially available or easy to synthesize. By applying an external AC electric field, we show that the apparently isotropic particles experience anisotropic interactions, which lead to the formation of colloidal oligomers. Moreover, those colloidal oligomers can “react” with others to form macro-colloidal molecules or two-dimensional non-close packed structures. We also illustrate the striking similarity between oligomers assembly and chemical reactions of real molecules. Our method can be used to generate complex patterns or to build complex building blocks, all based on simple spherical particles with isotropic properties. Because our method is physical in nature, its potential application to a broad range of particles with different chemical properties is envisioned.