폴리이미드 배향막의 편광 자외선 조사에 따른 액정 배향 메카니즘

김일형; 김욱수; 하기룡; Il Hyoung Kim; Wook-Soo Kim; Kiryong Ha

Polymer(Korea), Vol.26, No.2, 209-217, March, 2002

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폴리이미드 배향막의 편광 자외선 조사에 따른 액정 배향 메카니즘

Mechanism of Orientation of Liquid Crystal Molecules for Polarized UV-exposed Polyimide Alignment Layers

김일형, 김욱수, 하기룡^†

계명대학교 화학공학과

Il Hyoung Kim, Wook-Soo Kim, and Kiryong Ha^†

Department of Chemical Engineering, Keimyung University, Daegu 704-701, Korea

E-mail:

초록

편광 푸리에 변환 적외선 분광법과 자외선 분광법을 이용하여 액정 display (LCD)의 배향막으로 널리 사용되는 폴리이미드 (PI) 필름의 편광 자외선 (PUV) 조사에 따른 액정의 배향 메카니즘을 연구하였다. UV 측정 결과, PI 필름은 360 nm 이하 파장의 자외선을 주로 흡수하여 광화학 반응이 유도됨을 알 수 있었다. 또한, PUV가 조사된 PI의 경우, PI 분자들의 분해로 인해 FT-IR 흡수 피크들의 강도가 조사시간에 따라 감소하였고, 3244 cm(-1) 부근에서 완만한 곡선 형태의 새로운 피크가 형성되었다. 또한 조사된 PUV의 극성 방향에 평행한 PI 분자들의 우선적인 광분해 반응으로 인하여 PUV 조사 후 남아 있는 PI 분자들은 조사된 PUV 극성 방향과 수직 배향을 나타내었다. 하지만 러빙 처리된 PI 필름은 러빙 방향과 평행하게 PI 분자들의 재배향이 유도됨을 확인하였다. 또한 러빙 처리 및 PUV가 조사된 PI 배향막을 사용하여 제조된 액정 셀에서는 액정이 러빙 방향에 대해서는 평행하게, 조사된 PUV의 극성방향과는 수직으로 배향함을 확인하였다.

We studied the mechanism of orientation of polyimide molecules which were irradiated by polarized UV (PUV) using polarized Fourier transform infrared (FT-IR) spectroscopy and ultraviolet (UV) spectroscopy. According to the measured UV spectra, we found PI films mainly absorb UV light less than 360 nm wavelength, therefore, UV light less than 360 nm induces photochemical reaction of PI. PUV irradiation of PI films caused decrease of all peak intensities in the FT-IR spectra, except the newly formed broad peak at 3244 cm(-1), due to degradation of the PI molecules. The remaining PI molecules after photodegradation showed predominantly perpendicular molecular orientation to the irradiated PUV polarization direction, due to the preferential degradation of PI molecules parallel to irradiated PUV polarization direction. However the rubbing of PI films induced reorientation of the PI molecules parallel to the rubbing direction. We also investigated the alignment of the liquid crystal by rubbing or PUV irradiation. Liquid crystals align perpendicular to the PUV polarization direction and parallel to the rubbing direction.

Keywords:polyimide;polarized UV;liquid crystal;FT-IR;orientation

[References]

Allen G, "Comprehensive Polymer Science: The Synthesis, Characterization, Reactions & Applications of Polymers (First supplement)", Pergamon Press Ltd., New York, 301 (1992)
Yeh P, Gu C, "Optics of Liquid Crystal Displays", John Wiley & Sons, Inc., New York, 1 (1999)
Demus D, Goody J, Gray GW, Spiess HW, Vill V, "Handbook of Liquid Crystals", Wiley-VCH, New York, 732 (1998)
Lee JW, Sung SJ, Park JK, Synth. Met., 117, 271 (2001)
Bryan-Brown GP, Sage IC, Liq. Cryst., 20(6), 825 (1996)
Shannon PJ, Gibbons WM, Sun ST, Nature, 368(6471), 532 (1994)
Lu J, Deshpande SV, Gulari E, Kanick J, J. Appl. Phys., 80(9), 5028 (1996)
Lien A, John RA, Angelopoulos M, Lee KW, Takano H, Tajima K, Takenada A, Appl. Phys. Lett., 67(21), 3108 (1995)
Sakamoto K, Arafune R, Ito N, Ushioda S, Suzuki Y, Morokawa S, J. Appl. Phys., 80(1), 431 (1996)
Aerle NAJM, Barmentlo M, Hollering RWJ, J. Appl. Phys., 74(5), 3111 (1993)
West JL, Wang X, Ji L, Kelly JR, SID 95 Digest, 703 (1996)
Ghosh MK, Mittal KL, "Polyimides: Fundamentals and applications" Marcel Dekker Inc., New York, 18 (1996)
Hoyle CE, Anzures ET, Subramanian P, Nagarajan R, Creed D, Macromolecules, 25, 6651 (1992)
Lin AA, Sastri VR, Tesore G, Reiser A, Eachus R, Macromolecules, 21(4), 1165 (1988)
Ha K, West JL, Mol. Cryst. Liq. Cryst., 323, 129 (1998)
Ban BS, Kim YB, J. Appl. Polym. Sci., 75(14), 1728 (2000)
Demus D, Richter L, "Textures of Liquid Crystals", Verlag Chemie, New York, 32 (1978)
Wu S, Applied Optics, 26(16), 3434 (1987)
Ha K, West JL, Cryst. Liq. Cryst., 325, 13 (1998)
Smith BC, "Infrared Spectral Interpretation: A Systematic Approach", CRC Press LLC New York, 33 (1999)

[Referenced By]

[1] Allen G, "Comprehensive Polymer Science: The Synthesis, Characterization, Reactions & Applications of Polymers (First supplement)", Pergamon Press Ltd., New York, 301 (1992)

[2] Yeh P, Gu C, "Optics of Liquid Crystal Displays", John Wiley & Sons, Inc., New York, 1 (1999)

[3] Demus D, Goody J, Gray GW, Spiess HW, Vill V, "Handbook of Liquid Crystals", Wiley-VCH, New York, 732 (1998)

[4] Lee JW, Sung SJ, Park JK, Synth. Met., 117, 271 (2001)

[5] Bryan-Brown GP, Sage IC, Liq. Cryst., 20(6), 825 (1996)

[6] Shannon PJ, Gibbons WM, Sun ST, Nature, 368(6471), 532 (1994)

[7] Lu J, Deshpande SV, Gulari E, Kanick J, J. Appl. Phys., 80(9), 5028 (1996)

[8] Lien A, John RA, Angelopoulos M, Lee KW, Takano H, Tajima K, Takenada A, Appl. Phys. Lett., 67(21), 3108 (1995)

[9] Sakamoto K, Arafune R, Ito N, Ushioda S, Suzuki Y, Morokawa S, J. Appl. Phys., 80(1), 431 (1996)

[10] Aerle NAJM, Barmentlo M, Hollering RWJ, J. Appl. Phys., 74(5), 3111 (1993)

[11] West JL, Wang X, Ji L, Kelly JR, SID 95 Digest, 703 (1996)

[12] Ghosh MK, Mittal KL, "Polyimides: Fundamentals and applications" Marcel Dekker Inc., New York, 18 (1996)

[13] Hoyle CE, Anzures ET, Subramanian P, Nagarajan R, Creed D, Macromolecules, 25, 6651 (1992)

[14] Lin AA, Sastri VR, Tesore G, Reiser A, Eachus R, Macromolecules, 21(4), 1165 (1988)

[15] Ha K, West JL, Mol. Cryst. Liq. Cryst., 323, 129 (1998)

[16] Ban BS, Kim YB, J. Appl. Polym. Sci., 75(14), 1728 (2000)

[17] Demus D, Richter L, "Textures of Liquid Crystals", Verlag Chemie, New York, 32 (1978)

[18] Wu S, Applied Optics, 26(16), 3434 (1987)

[19] Ha K, West JL, Cryst. Liq. Cryst., 325, 13 (1998)

[20] Smith BC, "Infrared Spectral Interpretation: A Systematic Approach", CRC Press LLC New York, 33 (1999)