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Dielectrophoretic Assembly of New Colloidal Structures from Janus and Patchy Metallodielectric Particles

Orlin D. Velev1, Sumit Gangwal1, Amar B. Pawar2, and Ilona Kretzschmar3. (1) Department of Chemical and Biomolecular Engineering, North Carolina State University, College of Engineering 1, Box 7905, 911 Partners Way, Raleigh, NC 27695, (2) Department of Chemical Engineering, The City College of the City University of New York, Steinmann Hall, 140 ST. and Convent Avenue, New York, NY 10031, (3) Department of Chemical Engineering, The City College of City University of New York, 140th St. at Convent Ave., New York, NY 10031

“Janus” particles with two hemispheres of different polarizability or charge demonstrate a multitude of interesting effects 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. Here, we demonstrate the assembly of such Janus particles driven by high frequency (> 10 kHz) AC electric fields. 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 in fields of similar frequency and intensity. Even more unusual types of structures are formed in suspensions of "patchy" particles, produced by glancing angle metal deposition. These particles assemble in two or more directions, pre-programmed by the size and orientation of the patches. The experimental results of the assembly of Janus and patchy particles in the electric field are interpreted by means of numerical simulations of the electric energy of the system. These experimental and modeling techniques could be used to guide the experiment of directed assembly of other types of anisotropic particles.