EVENT DETAILS AND ABSTRACT

Title: Driven Granular Media: Phase Transitions, Patterns and Vortices
Speaker: Igor Aronson
Speaker Info: Argonne National Laboratory
Brief Description:
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Abstract:

Large ensembles of small particles display fascinating collective behavior when they acquire an electric charge and respond to competing long-range electromagnetic and short-range contact forces. Many industrial technologies face the challenge of assembling and separating such single- or multi-component micro and nano- size ensembles. The dynamics of conducting microparticles in strong electric field in the air or in deep vacuum was studied in Refs. [1,2]. Phase transitions and clustering instability of the electrostatically driven granular gas were found. A continuum model for the phase separation and coarsening in was formulated in terms of a Ginzburg-Landau equation subject to conservation of the total number of grains. In the regime of well-developed clusters, the continuum model is used to derive "sharp-interface" equations that govern the dynamics of the inter-phase boundary. The situation is remarkably different when the cell filled with poorly conducting liquid (toluene-ethanol mixute). We have found that metallic particles form a rich variety of phases not observed in air-filled cell. These phases include static precipitates: honeycombs lattices and Wigner crystals; and novel dynamic condensates: toroidal vortices and pulsating rings [3]. The observed phenomena are attributed to interaction between particles and electro-hydrodynamic flows produced by the action of the electric field on ionic charges in the bulk of liquid.