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Nanocomposites are created by doping host polymers with nanoparticles that typically have higher or lower refractive indices. The ability to tailor the mechanical and optical performance of these composites has led to their increased use in transparent materials. Nanocomposites maintain the elastic properties of the binding polymers and exhibit infinite refractive index tunability between the limits of the system. These unique properties provide distinct benefits for multilayer, thin-film optical filters. Because the nanoparticles are dispersed in a fluid or bound in a polymer matrix in use, toxicity risks that may be associated with raw particles are reduced. Using a stable dispersion of titanium dioxide nanoparticles and a UV curable monomer, we were able to design and produce several quarter-wave filters that demonstrate control of the height and width of the passband through adjustment of the organic/inorganic ratio and layer count. The volume loading of the metal oxides can be adjusted from zero to near the theoretical packing density of spheres, allowing refractive index to be controlled over a large range. Because metal oxide particles exhibit high UV absorption, these additives provide UV protection to the host polymer and the filter's substrate. Additionally, significant improvements in abrasion resistance are often observed in films loaded with nanoparticles at the concentrations of interest. |
