Synthesis of Highly Fluorinated Monodisperse Colloids for Low Refractive Index Crystalline Colloidal Arrays

Abstract

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.

Immobilized Highly Charged Colloidal Crystals: A New Route to Three-Dimensional Mesoscale Structured Materials

“…Hydrogels: The hydrogels were prepared according to the method applied by Asher et al [15] The colloidal suspension, acrylamide, crosslinker, and photoinitiator were mixed and shaken with ion-exchange resin. The mixture was injected into a cell between a quartz plate and a stainless steel electrode.…”

“…At low ionic strength these systems self-assemble to form liquidlike, glasslike, or crystalline structures, [14] which can be immobilized in a crosslinked polyacrylamide hydrogel. [15] These hydrogels can be applied as chemical sensors or as ™entropic traps∫ for the separation of macromolecules. [16] Our experiments show that such hydrogels are also suitable templates for the preparation of mesoscale ordered metals.…”

A combined 3D and 2D light scattering study on aqueous colloidal model systems with tunable interactions

“…To this end, the fluorinated monomer 2,2,3,3,4,4,4-heptafluorobutyl methacrylate (FBMA) has been successfully used to synthesize monodisperse particles with a low refractive index via emulsion polymerization and the system was shown to form well-ordered crystalline colloidal arrays. 33 Further effort has led to the production of FBMA particles with radii between 50 nm to 700 nm. 34 However, such particles are susceptible to irreversible aggregation upon salt addition or under compression by centrifugation, as they are solely stabilized through electrostatic repulsion (ER) in aqueous solution.…”

Colloidal Crystals in Latex Films: Rubbery Opals

“…Deformation of the films results in a shift of the reflected light wavelength. deionized water, [18] monomers [12] or hydrogels. [19] Quite different from these approaches, which exploit the selforganisation of spheres, are microtechnical methods of lithography and etching, which yield two-dimensional photonic crystals with cylindrical pores in silicon.…”