Colloids are important for our daily life and modern technologies. Among which colloidal particles with asymmetric properties in geometry, surface functionality, and chemical composition emerge as an important family of the colloidal genome. Scientifically, the out-of-equilibrium behaviors of these colloids are fundamentally different from conventional particles because of their broken symmetry in particle properties, colloidal interactions, and surrounding fluid flow. In this talk, we will report our recent studies of the induced motion of asymmetric colloids under externally applied electric and magnetic fields. We will first describe a new type of particle propulsion mechanism that is based on breaking the symmetry of electrokinetic flow using low power AC electric fields. We show that dielectric colloidal dimers with broken symmetry in geometry, composition, or interfacial charges can all propel in directions that are perpendicular to the applied ac electric field. The asymmetry in particle properties ultimately results in an unbalanced electrohydrodynamic flow on two sides of the particles. Consistent with scaling laws, the propulsion direction, speed, and orientation of dimers can be conveniently tuned by frequency. For the Janus magnetic particles, we will further show that the particle’s trajectory can be precisely and conveniently controlled by a combination of AC electric field and DC magnetic field. The uniform magnetic field controls particle’s orientation while the electric field creates an induced-charge electro-osmotic flow and actuates the particle. A number of non-trivial particle trajectories will be demonstrated. The new propulsion mechanism revealed here can be useful for building colloidal-based metamaterials and studying collective behavior of active matter.<br/>

External-field induced propulsion of particles with broken symmetry

253rd National Meeting (2017)

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