Emergence of colloidal patterns in AC electrical fields

TL;DR

This paper investigates how various microparticles organize into complex patterns under AC electrical fields, revealing a universal electrokinetic mechanism and validating it through simulations and theory.

Contribution

It demonstrates the universal emergence of colloidal patterns in AC fields across diverse particles and provides a quantitative, parameter-free theoretical explanation.

Findings

Patterns form across multiple particle types

Hydrodynamic interactions predict pattern formation

Simulations match experimental observations

Abstract

Suspended microparticles subjected to AC electrical fields collectively organize into band patterns perpendicular to the field direction. The bands further develop into zigzag shaped patterns, in which the particles are observed to circulate. We demonstrate that this phenomenon can be observed quite generically 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 well understood in terms of second order electrokinetic flow, which correctly predicts the hydrodynamic interactions required for the pattern formation process.Brownian particle simulations based on these interactions accurately recapitulate all of the observed pattern formation and symmetry-breaking events, starting from a homogeneous particle suspension. The emergence of the formed patterns can be predicted quantitatively within a parameter-free theory.