(351f) Dielectrophoretic Assembly of Janus and Patchy Particles in AC Electric Fields

The application of external fields to Janus particles (whose halves are physically or chemically different) is a rapidly expanding research field, as it can be an efficient means of programmed assembly of novel materials. Janus particles were prepared by coating dielectric microspheres with a conductive metal layer on one hemisphere. The phase space for AC electric field intensity and field frequency was explored for these particles on a glass surface between two electrodes. A rich variety of structures and dynamics were uncovered, which are different than the ones in the directed dielectrophoretic assembly of plain dielectric or plain conductive particles. Even more unusual types of new structures formed when high frequency (> 200 kHz) AC electric fields are applied to suspensions of ?patchy? particles. The patchy particles, produced by glancing angle metal deposition, have either a single metallic patch that is ~ 10% of the total latex particle surface or two metallic patches (each covering 25% of the total surface) on opposite poles of the particle. These patchy particles assemble perpendicular to or at an angle to the applied field direction, pre-programmed by the size and orientation of the patches. The patchy particles formed metallodielectric crystals of unusual symmetry at high enough concentrations of particles. The assembly of both Janus and patchy particles in the electric field was further investigated by using electrostatic simulations to calculate the electric energy of the system to determine the most favorable particle orientation and chain configuration. The simulation results indicate that the patchy particles interact as quadruples, which explains why they assemble into multi-directional chains. These experimental and modeling techniques could be used to engineer the processes of directed assembly of other types of anisotropic particles.