Reactive CeO2 nanofluids for UV protective films

Abstract

We investigate surface modification by organo-trimethoxysilanes of nano-ceria and if such surface-modified nano-ceria can be transformed into solvent-free nanofluids. We also examine whether simultaneous modification with ionic liquid salts and with acrylate groups yields nanofluids suitable for forming UV-protective films and clear coatings by UV-initiated polymerization. Nominally 3nm diameter CeO2 was successfully synthesized and surface decorated with an ionic liquid salt and with acrylate groups to produce a core/shell structured solvent-free nanofluid after ion exchange of chloride for a soft polyoxyethylene sulfonate anion. This room temperature nanofluid melts at about −10°C and exhibits a glass transition at about −71°C. The melting enthalpy, about 19J/g, corresponds approximately to the gain in surface free energy of such nanofluid particles upon transforming from the solid state to liquid state. Robust films were made by UV photoinitiation of this nanofluid in combination with ethylene glycol dimethacrylate and with a polyoxyethylene diacrylate to yield cross-linked films with absorption coefficients α350nm=6.6±0.8cm2/mg and α300nm=24.5±3.5cm2/mg. Average near UV protection over 300–350nm of 1–3 optical density units can be obtained with 0.065–0.19mg/cm2 of CeO2. These materials appear almost three-fold more effective, per unit ceria, than previously reported clearcoats of nanoceria.