Emergence of Colloidal Patterns in AC Electrical Fields
Florian Katzmeier, Bernhard Altaner, Jonathan List, Ulrich Gerland, and Friedrich Simmel
Suspended microparticles subjected to AC electrical fields collectively organize into band patternsperpendicular to the field direction. The bands further develop into zigzag shaped patterns, in whichthe particles are observed to circulate. We demonstrate that this phenomenon can be observed quitegenerically by generating such patterns with a wide range of particles: silica spheres, fatty acid, oil,and coacervate droplets, bacteria, and ground coffee. We show that the phenomenon can be wellunderstood in terms of second order electrokinetic flow, which correctly predicts the hydrodynamicinteractions required for the pattern formation process. Brownian particle simulations based on theseinteractions accurately recapitulate all of the observed pattern formation and symmetry-breakingevents, starting from a homogeneous particle suspension. The emergence of the formed patternscan be predicted quantitatively within a parameter-free theory.