Electrolyte-dependent multiparticle motion near electrodes in oscillating electric fields.

The directed assembly of micrometer-scale particles into hexagonal lattices on electrodes was probed by subjecting them to electric fields oscillating at 100 Hz. Solutions of KOH, NaHCO(3), and KCl were used because previous investigations of particle pair behavior had shown that an electrolyte-dependent phase angle dictates whether two particles aggregate or separate at low frequencies. Here it was found that particle ensembles, aggregating or separating, adopt a 2D hexagonal lattice in both cases; the difference appears in the particle spacing. For electrolytes such as NaHCO(3) and KCl, where two isolated particles aggregate, the gap between particle edges is between 1 and 1.5 particle diameters; in KOH, where two particles tend to separate, the interparticle spacing is several diameters.