Field-Induced Interfacial Properties of Gold Nanoparticles in AC Microelectophoretic Experiments

Electrophoretically induced aggregation of Au nanoparticles has been studied in the past especially in relation to interparticle interactions or particle/surface interactions leading to self-organization of particles into structures. The work described here focuses on field-induced interfacial changes preceding the aggregation. We show that, in strong AC electric fields, comparable to those used for electrophoretic aggregation of microwires and 2D crystals at electrode surfaces, slow field-dependent variations in the nanoparticle mobility occur. These variations in mobility are accompanied by a few orders of magnitude increase in the adsorption rate of colloidal gold nanoparticles, onto a similarly charged silica surface. The onset time of adsorption strongly depends on the applied AC field intensity. A qualitative model aimed at explaining the observed field-induced adsorption of negatively charged gold particles on a similarly charged silica surface is proposed. The model is based on the idea that the adsorbed ion distribution at the particle surface is influenced by the applied electric field. The result of prolonged electric field exposure is a nonuniform distribution of charge across the nanoparticle surface, which renders orientation-dependent adsorption possible.