Synthesis of highly fluorinated monodisperse colloids for low refractive index crystalline colloidal arrays

Highly charged fluorinated monodisperse spherical particles of diameters between 50 and 250 nm were synthesized from 1H,1H-heptafluorobutyl methacrylate by emulsion polymerization. These particles have a low refractive index of 1.386. High particle surface charge densities were obtained by minimizing the polymer molecular weight. These colloids formed well-ordered crystalline colloidal arrays (CCAs), after dialysis and ion exchange, which Bragg diffract light at wavelengths from the near-IR down to 270 nm in the UV. The diffraction bandwidths in water are very narrow (<10 nm) due to the closeness of refractive index of the colloidal particles to that of water. These CCAs are excellent materials for narrow band notch optical filters. In addition, these fluorinated CCAs can be easily refractive index matched to a predominately aqueous medium. We have covalently attached dyes to the colloidal particles to prepare absorbing CCAs. We photopolymerized these dyed CCAs within a polyacrylamide matrix to form polymerized crystalline colloidal array (PCCA). These semisolid PCCAs can withstand vibrations, ionic impurity addition, and thermal shocks while maintaining the CCA ordering. The medium within the PCCA can easily be exchanged to exactly refractive index match the CCA. These refractive index matched dyed PCCAs may have applications in optical limiting, computing, and nanosecond fast optical switching devices as discussed in the accompanying paper.