  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 solvent 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 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 repulsion 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.
