Two modes of linear layer-by-layer growth of nanoparticle-polylectrolyte multilayers and different interactions in the layer-by-layer deposition

The structure of the multilayer assemblies of yttrium iron garnet nanoparti cles (YIG) with polyelectrolytes was investigated with the emphasis on the control of the particle density in the adsorption layers. It was found that the growth of YIG films prepared by the layer-by-layer assembly can occur via two deposition modes: (1) sequential adsorption of densely packed adsor ption layers (normal growth mode) and (2) in-plane growth of isolated parti cle domains (lateral expansion mode). Importantly, the dependence of the op tical density on the number of deposition cycles remains linear in both cas es. Microscopy results indicate that the origin of the lateral growth is in the interplay of particle/particle and particle/polyelectrolyte interactio ns rather than in a substrate effect. The lateral expansion mode is a gener al attribute of the layer-by-layer deposition and can be observed for vario us aqueous colloids. Fur the preparation of sophisticated multifunctional a ssemblies on nanoparticles, the film growth via domain expansion should be avoided, and therefore, one must be able to control the growth pattern. The switch from lateral to normal growth mode can be effected by grafting char ged organic groups to YIG nanoparticles. Hydrophobic interactions between t he hydrocarbon groups of the modified YIG and polyelectrolyte significantly increase the attractive component of the particle/polyelectrolyte and part icle/particle interactions. The films from modified YIG display densely pac ked nanoparticle layers with a greatly reduced number of defects.