Fine-tuning the assembly of highly stable oppositely charged cerium oxide nanoparticles in solution and at interfaces

Abstract

Abstract In this work we have shown how to fine-tune the electrostatic assembly of oppositely charged cerium oxide nanoparticles (NPs) in a solution and at a solid/liquid interface. In a first stage, we have developed anionic and cationic CeO2 NPs stable in a highly saline environment and a wide pH range via efficient electro-steric interactions. Anionic NPs were obtained by coating bare NPs with short polyacrylic acid (PAA) chains through a Precipitation-Redispersion method. Whereas cationic NPs were formulated by tethering branched polyethyleneimine (bPEI) chains onto PAA-coated ceria NPs through the formation of amide bonds with the help of imide cross-linkers. The covalent attachment of bPEI chains was evidenced through NMR characterizations while thermogravimetric (TGA), dynamic light scattering (DLS) and zeta potential measurements confirmed the successful encapsulation by both types of weak polyelectrolytes. In a second stage, the high stability of both NP dispersions toward high ionic strength (up to 4 M NH4Cl) enabled to generate hybrid clusters in a controlled way by fine tuning their co-assembly following a desalting transition route monitored by DLS. In a last part, we have extended our approach to surfaces and generated all-nanoparticle layer grown directly from a liquid/solid interface monitored by Quartz Crystal Microbalance (QCM). Such thin nano-clustered layer with tunable and relatively high volume fraction of ceria NPs represents a promising platform to impart functional coatings onto metal, ceramic and polymer substrates.