Effects of Fabrication Conditions on Electro-optic Properties of UV-Cured Polymer/Liquid Crystal Composite Films

UV 경화형 고분자/액정 복합체의 제조 조건에 따른 전기광학적 특성

  • Park, Se Kwang (Department of Electric and Electronic Engineering, Kyungpook Univ.) ;
  • Park, Lee Soon (Department of Polymer Engineering, Kyungpook National Univ.) ;
  • Keum, Chang Dae (Department of Polymer Engineering, Kyungpook National Univ.) ;
  • Seok, Jae Wook (Department of Polymer Engineering, Kyungpook National Univ.) ;
  • Ahn, Won Sool (Department of Chemical Engineering, Keimyung Univ.)
  • 박세광 (경북대학교 전기전자공학부) ;
  • 박이순 (경북대학교 고분자공학과) ;
  • 금창대 (경북대학교 고분자공학과) ;
  • 석재욱 (경북대학교 고분자공학과) ;
  • 안원술 (계명대학교 화학공학과)
  • Received : 1998.03.14
  • Accepted : 1998.05.06
  • Published : 1998.08.10

Abstract

Polymer dispersed liquid crystal(PDLC) composite films were made by polymerization induced phase separation method using UV-curing to investigate the effect of fabrication conditions, such as photoinitiator concentration, film thickness, polymerization temperature, and electric field during polymerization, etc., on the electro-optic properties. As the amount of photoinitiator increased, the driving voltage of PDLC device increased due to the increase of small-size liquid crystal phases. This was considered as the results from the increased interfacial area between liquid crystal (LC) and polymer matrix, since LC molecules at the interfacial regions were relatively difficult to response for the applied electric field. When the higher molecular weight oligomer (PTDA-1000) was used as matrix, the initial transmittance was observed to be relatively higher than that for the lower molecular weight oligomer (PTDA-250). Saturation transmittance for PTDA-1000 was observed at relatively lower voltage than that for PTDA-250, of which transmittance was not saturated even at 60 V. As polymerization temperature increased, the initial transmittance of resulting PDLC film increased due to the larger LC droplets formation and the more matched refractive index between LC and matrix than those cases for the lower polymerization temperature. Though driving voltage decreased for the thinner film, it was considered that optimum thickness of the film should be maintained to get some practical contrast, which is the ratio of off- and on-state transmittance. Furthermore, electro-optic properties such as initial transmittance, driving voltage, and response time were observed to be considerably affected by application of external field during polymerization.

Keywords

Polymer Dispersed Liquid Crystal;PDLC;Polymer Network Liquid Crystal (PNLC);UV Curing

Acknowledgement

Supported by : 한국과학재단

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