Diatoms are of interest to the materials research community because of their ability to create highly complex and intricate silica structures under physiological conditions: what these single-cell organisms accomplish so elegantly in nature requires extreme laboratory conditions to duplicate-this is true for even the simplest of structures. Following the identification of polycationic peptides from the diatom Cylindrotheca fusiformis, simple silica nanospheres can now be synthesized in vitro from silanes at nearly neutral pH and at ambient temperatures and pressures. Here we describe a method for creating a hybrid organic/inorganic ordered nanostructure of silica spheres through the incorporation of a polycationic peptide (derived from the C. fusiformis silaffin-1 protein) into a polymer hologram created by two-photon-induced photopolymerization. When these peptide nanopatterned holographic structures are exposed to a silicic acid, an ordered array of silica nanospheres is deposited onto the clear polymer substrate. These structures exhibit a nearly fifty-fold increase in diffraction efficiency over a comparable polymer hologram without silica. This approach, combining the ease of processability of an organic polymer with the improved mechanical and optical properties of an inorganic material, could be of practical use for the fabrication of photonic devices.
Holographic reflection gratings in polymer-dispersed liquid crystals (H-PDLCs) were formed
by thiol−ene photopolymerization. Using UV laser light and a single prism, electrically
switchable reflection gratings in blue, green, yellow, and red colors were fabricated. Results
indicate that thiol−ene polymers function as better hosts for H-PDLC than multifunctional
acrylate as matrixes. These differences are the result of a much different temporal structure
development caused by fundamental differences in the polymerization propagation mechanism: a step-growth addition mechanism for the thiol−ene system compared to a chain-growth addition mechanism in multifunctional acrylates. Morphology studies by TEM support
these conclusions, as striking differences in droplet shape and uniformity are observed.
Discrete nematic droplets with a nearly spherical shape were seen. Thiol−ene polymers offer
lower switching fields, higher diffraction efficiencies, better optical properties, and higher
thermal stabilities. The response times of the thiol−ene gratings were five times slower
than those of acrylates.
Holographic photopolymerization is a flexible, simple, one‐step technique to create defect‐free, sub‐micrometer patterns of particles over large dimensions. These permanent structures can be formed in a matter of seconds. The resulting Bragg gratings exhibit substantial diffraction efficiencies. The Figure shows a cross‐sectional fracture surface of a transmission grating formed using clay powder.
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