Coated colloids with tailored optical properties

Tailored optical properties have been imparted to polystyrene (PS) colloids of various sizes by the layer-by-layer (LbL) assembly of silica-coated gold (Au@SiO2) or silica-coated silver (Ag@SiO2) nanoparticles with different shell thicknesses and an electrostatically bridging polyelectrolyte, poly(diallyldimethylammonium chloride) (PDADMAC). The spectral position of the surface plasmon band of the composite colloid spheres is tailored through (i) the type of silica-coated nanoparticles used, (ii) the thickness of the silica shell, and (iii) the number of nanoparticle layers deposited. For thin silica shells (< 10 nm), the number of nanoparticle layers deposited on the PS particles influences the plasmon band position due to electromagnetic coupling between neighboring metal nanoparticle cores. However, in the case of thick silica shells (> 18 nm), nanoparticle core-core interparticle interactions are fully prevented and the plasmon band position is unaffected. Additionally, silica dissolution with HF leads to compact nanoparticulate metal layers on the PS spheres. The particles prepared are expected to find use as novel building blocks with unique optical properties for integration into advanced materials.