Formation of Dense Nanoparticle Monolayers Mediated by Alternating Current Electric Fields and Electrohydrodynamic Flows

Mono layers comprising oppositely charged metal nanoparticles are deposited onto conductive surfaces upon application of ac fields of frequency ranging from 0.1 to 800 kHz. It is found that surface coverage depends on the frequency and is maximal at similar to 300 kHz, for which the deposited coatings feature large, hexagonally close packed domains. The observed trends are rationalized by a model in which ac forcing induces hydrodynamic flows around the particles. These flows, in turn, translate into additional interparticle attractions facilitating dense particle packing.