Interfacial Activity of Phosphonated-PEG Functionalized Cerium Oxide Nanoparticles

In a recent publication, we have highlighted the potential of phosphonic acid terminated PEG oligomers to functionalize strong UV absorption cerium oxide nanoparticles,(1) which yield suspensions that are stable in aqueous or organic solvents and are redispersible in different solvents after freeze-drying. In the present work, we highlight the interfacial activity of the functional ceria nanoparticles and their potential to modify hydrophobic surfaces. We first investigated the phosphonated-PEG amphiphilic oligomers behavior as strong surface active species forming irreversibly adsorbed layers. We then show that the oligomers interfacial properties translate to the functional nanoparticles. In particular, the addition of a small fraction of phosphonated-PEG oligomers with an extra C16 aliphatic chain (stickers) into the formulation enabled the tuning of (i) the nanoparticles adsorption at the air/water, polystyrene/water, oil/water interfaces and (ii) the particle/particle interaction in aqueous solutions. We also found that dense and closely packed two-dimensional monolayers of nanoceria can be formed by spontaneous adsorption or surface compression using a Langmuir trough. A hexagonal organization controlled by reversible and repulsive interaction has been characterized by GISAXS. Mono- or multilayers can also be stably formed or transferred on solid surfaces. Our results are key features in the field of polymer surface modification, solid-stabilized emulsions (Pickering), or supracolloidal assemblies.