Holographic polymer dispersed liquid crystal reflection gratings formed by visible light initiated thiol-ene photopolymerization

• Published in: Polymer (Guilford) Vol. 47; no. 12; pp. 4411 - 4420
• Main Authors: Natarajan, Lalgudi V., Brown, Dean P., Wofford, Jeremy M., Tondiglia, Vincent P., Sutherland, Richard L., Lloyd, Pamela F., Bunning, Timothy J.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 31.05.2006; Elsevier
• Subjects: Applied sciences; Exact sciences and technology; Fundamental areas of phenomenology (including applications); Holographic recording materials; optical storage media; Holography; Liquid crystals; Optical materials; Optics; Physicochemistry of polymers; Physics; Polymerization; Polymers and radiations; Visible photoinitiator; Holography; Visible photoinitiator; Liquid crystals; Rhodamine; Nitrogen heterocycle; Titanium complex; Priming activity; Metallocene; Polyaddition; Allylic compound; Crosslinked polymer; Visible radiation; Optical material; Recording material; Boron compound; Thiol; Electrooptical properties; Experimental study; Reflection grating; Photoinitiator; Thioplast; Polymer dispersed liquid crystals; Laser beam; Morphology; Holographic grating; Comparative study
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/j.polymer.2006.04.033

Visible laser light of wavelengths 442, 488 and 532 nm was used to write holographic reflection gratings with notches into the infra-red spectral region in polymer dispersed liquid crystals (H-PDLC). The gratings were formed by the spatially periodic phase separation of nematic liquid crystal during thiol-ene photopolymerization. An organic titanocene based complex, Rhodamine 6G (Rh6G) and Pyrromethene 597 (Pym) dyes in combination with benzoyl peroxide, were used as initiators. Using visible laser light and a single prism, electrically switchable reflection gratings with notches in the blue, green, yellow, red, and near infra-red (NIR) spectral regions were fabricated using angle tuning. The photophysics of the initiator dyes was studied by absorption and fluorescence spectroscopy. Morphology studies by TEM showed a periodic distribution of discrete nematic droplets of nearly spherical shape. The development of visible photoinitiator systems broadens the range of fabrication wavelengths of dynamic reflection filters using inexpensive visible lasers.