“Janus” particles with two hemispheres of different polarizability or charge demonstrate a multitude of interesting behaviors in external fields. We reported earlier how particles with one metallic hemisphere and one dielectric hemisphere self-propel in low-frequency alternating current (AC) electric fields.¹ Here, we demonstrate the assembly of such Janus particles driven by high frequency (> 10 kHz) AC electric fields. We investigated the field-induced dielectrophoretic (DEP) force, flow fields, and structure of the assemblies. The phase space for electric field intensity and field frequency is explored for particle concentrations large enough to form a monolayer on a glass surface between two gold electrodes. A rich variety of metallodielectric particle structures and dynamics are uncovered, which are very different than the ones in directed assembly of plain dielectric or plain conductive particles when fields of similar frequency and intensity are applied. The metallodielectric particles assemble into new types of particle chain structures, where the metallized halves of neighboring particles align into conductive lanes throughout the alternating chain. The alternating chains are confined together to form two-dimensional (2D) metallodielectric crystals. The experimental results of the orientation of Janus particles in the electric field and the formation of alternating chains are interpreted by means of numerical simulations of the electric energy of the system. The experimental and modeling techniques could be used to guide the experiment of directed assembly of other types of anisotropic particles. The field-driven assembly of Janus metallodielectric particles may find applications as liquid-borne microcircuits and materials with directional electrical and heat transfer.

1. Phys. Rev. Lett. 2008, 100, 058302.