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Proceedings Paper

Non-symmetric broadening of the reflection notch in polymer stabilized cholesteric liquid crystals
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Paper Abstract

Non-symmetric broadening (to the blue side) of a cholesteric reflection notch was observed when a cell containing diacrylate and monoacrylate nematic LC monomers, a chiral dopant, nematic LC and a photoinitiator was exposed to very low intensity (microwatts) of 335 nm UV light. At very low intensity, the polymerization rate is very slow and takes a long time to complete as observed by real-time monitoring experiments. The polymerized scaffold templates the original liquid crystal helical structure. The 335 nm light is highly absorbed by the system which generates an intensity gradient throughout the thickness of the cell. This gradient produces a free radical density gradient in the later stage of the polymerization when diffusion is slowed by the growing polymer network. Since more monomer is consumed at the front half of the cell, a counter diffusion of chiral dopant towards the cell backside is observed. This leads to a local increase in the HTP causing a local blue shift of the notch wavelength. The net result observed in transmission is a broadening of the reflection bandwidth from 70 nm to 200 nm where the broadening occurs only to the blue side of the original notch. By varying the intensity of the UV source on one side of the substrate, the broadening magnitude could be controlled. Simultaneous UV illumination from both sides of the cell reduced the broadening considerably. The broadened notch was switchable at high electrical field (20V/μm).

Paper Details

Date Published: 17 August 2010
PDF: 11 pages
Proc. SPIE 7775, Liquid Crystals XIV, 77750Z (17 August 2010); doi: 10.1117/12.861367
Show Author Affiliations
Lalgudi V. Natarajan, SAIC (United States)
Jimmy R. Voss, Air Force Research Lab. (United States)
Vincent P. Tondiglia, SAIC (United States)
Deng-Ke Yang, Liquid Crystal Institute (United States)
Timothy J. White, Air Force Research Lab. (United States)
Timothy J. Bunning, Air Force Research Lab. (United States)

Published in SPIE Proceedings Vol. 7775:
Liquid Crystals XIV
Iam Choon Khoo, Editor(s)

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