8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

Wed 711:10-14:00P5.157Nonequilibrium magnetic colloids at a liquid/liquidinterface: dynamic self-assembly and self-propulsionAlexey Snezhko 11 Argonne National Laboratory, 9700 S. Cass Avenue, 60439, Argonne, United States ofAmericaEnsembles of interacting particles with complex interaction profiles subject to external periodicforcing often develop nontrivial collective behavior. Emergent phenomena in magnetic colloidalensembles suspended at liquid-liquid interfaces and driven out of equilibrium by alternating magneticfields is investigated. Experiments reveal a new type of non-trivially ordered dynamic selfassembledstructures -asters emerging in such system in a certain range of excitation parameters.Transition between different self-assembled phases with parameters of external driving magneticfield is observed. Unusual magnetic ordering of the dynamic structures is revealed. Novel structuresare attributed to the interplay between surface waves, generated at the liquid/liquid interfaceby the collective response of magnetic microparticles to the alternating magnetic field, and hydrodynamicfields induced in the boundary layers of both liquids forming the interface. Two types ofmagnetic order is reported. We show that self-assembled aster structures develop self-propulsionin the presence of a small in-plane dc magnetic field. The speed of locomotion can be effectivelytuned by the amplitude of the dc field. Effective particle manipulation is demonstrating by thesenovel structures.157