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Park, Lee Soon
School of Materials Science and Engineering
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  • Flexible OLED new materials, process and fabrication
  • Touch Screen Panel(TSP) new materials and process new materials and process
  • Nano-materials synthesis and application (Ag nano-wire and metal mesh electrode)

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Structural effect of photoinitiators on electro-optical properties of polymer-dispersed liquid crystal composite films

Cited 17 times inthomson ciCited 16 times inthomson ci
Title
Structural effect of photoinitiators on electro-optical properties of polymer-dispersed liquid crystal composite films
Author
Seok, JWHan, YSKwon, YPark, Lee Soon
Keywords
composites; phase separation; photopolymerization; dispersions; DROPLETS; BEHAVIOR; DISPLAY
Issue Date
2006-01
Publisher
WILEY-BLACKWELL
Citation
JOURNAL OF APPLIED POLYMER SCIENCE, v.99, no.1, pp.162 - 169
Abstract
Two types of photoinitiators were synthesized: (1) a alpha,omega-telechelic oligomeric photoinitiator, by the reaction of poly(propylene glycol) diglycidylether (PPGDGE) and 2-hydroxy-2-methyl-1-phenyl-propan-1-one (Darocur 1173), and (2) a polymeric photoinitiator, by copolymerization of a monomer that had a liquid crystalline property, 4-[omega-(2-methylpropenoyloxy)decanoxy]-4'-cyanobiphenyl, with a vinyl monomer that had a photosensitive group. For comparison, low-molecular-weight (low-MW) photoinitiator (Darocur 1173) also was used. Attention was directed to the structural effect of the photoinitiators on the electro-optical properties of polymer-dispersed liquid crystal (PDLC) film in which the LC phase occupied a major volume (80 wt % of the composite film). For the preparation of PDLC films by the polymerization-induced phase separation method, the optimum UV-curing temperature was observed at 50 degrees C, a temperature slightly higher than the cloud temperature (T-cloud) of the low-MW LC/matrix-forming material mixture. It was found that the electro-optical performance of the PDLC cell fabricated with the oligomeric or polymeric photoinitiator was better than that of the PDLC cell made with a low-MW photoinitiator (Darocur 1173), exhibiting lower driving voltage (V-90) and higher contrast ratio under identical formulation conditions. Oligomeric photoinitiators allowed premature phase separation between the LC and matrix phases, resulting in relatively pure LC-rich phases. For the polymeric photoinitiator, incorporation of mesogenic moieties into the photoinitiator resulted in not only a well-defined LC/matrix morphology but also in low driving voltage (V-90) because of reduced friction at the LC/matrix interfaces. (c) 2005 Wiley Periodicals, Inc
URI
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DOI
10.1002/app.22446
ISSN
0021-8995
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MSE_Journal Papers
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