Composites of ordered colloidal crystals of amorphous monodisperse silica particles in amorphous poly(methyl acrylate) (PMA) films selectively Bragg diffract visible light. The 153 nm diameter colloidal silica particles coated with 3-(trimethoxysilyl) propyl methacrylate (TPM) form colloidal crystals in methyl acrylate (MA) monomer, and the crystal order is locked into place by polymerization of the MA. Bragg diffraction from the films is detected spectrophotometrically as narrow peaks of low % transmission (%T)of visible light normal to the film plane. The diffraction wavelength is tuned by varying the d-spacing of the crystal lattice and by varying the Bragg angle. Variation in the lattice spacing is achieved via the particle size or particle concentration, uniaxial stretching of the composite, and swelling the composite with monomers such as styrene or MA followed by photopolymerization of the imbibed monomers. Films that diffract from 434 to 632 nm have been prepared. The crystal structures of the precursor dispersions of TPM-silica in MA and of the composites have been modeled as fcc and rhombohedral respectively, although the degree of order of the materials is too low to permit confirmation by ultra small angle X-ray diffraction.
C60 and its derivatives are potential optical limiting materials due
to reverse saturable absorption of visible light. To obtain thorough dispersion
of C60 derivatives into clear polymer films, we have copolymerized C60 with
styrene and with methyl methacrylate. The products are mixtures of branched
copolymers containing many C60 units per macromolecule and linear homopolymers.
NASA/Marshall Space Flight Center, Space Sciences Laboratory's Microgravity Science and Applications Division and AMMSA (The Alliance for Microgravity Materials Science and Applications). AMMSA is jointly Operated by the Universities Space Research Association (USRA) and The University of Alabama in Huntsville (UAH)
Contact: Sue
Zarger, 205-544-2910
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