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kJª 2V® ËB f(flat panel) júb^Ê âæÎ liquid crystal dispay(LCD)ê Ý6 VÆ Â/& âênê Z{ âþV çš

û $– nêV ޚ " šÒ ÊÒ §ÿ®B ² ÚÒ&r nêÒ “ò®6 Þê gê² júb^Ê âæÊ:. N FÂ&rê LCD þš rç¶ ¢ šnKkÎ ·k †û& V² FÂÒ nß

®V:. Z LCD rÆ Kk&rê îÒ¶ G® òš Êÿ®B v

†f& ª[r polyimide(PI) šÚš ² û’² Òk®â Ž

šÚ Z ·k Úæ:® †ûš v®ê ëš ÿ®6 Þ:.^1,2 ÊB² rubbingë– i– ÊW® 6Úæ šÚ& žkW’² Wÿ¶

n Þê ûf ¢Ž& Z Kk& Wÿn6 Þ" g_ Kk’² Î

®B nnnê ’, kZ† G® ŽrfR LCD® ז 2ÒW Ž

Kk® rr& $– VBÊ þÊ6 Þ:. gn§‡ 6ÚæÒ ·k

†û’² Êÿ² g†û ë– šg_ ëÊr †Ê® rubbing

ëÊ Vê BB Žrf:š ʶ n Þê ûfš V6 Þ ÊÒ Êÿ² ·k †û FÂV ßn6 Þ:.^3-5

gn§‡ 6ÚæÒ LCD® ·k †û Kk& Wÿ®† ZÊrê gn§& ®®B 6Úæ šÚ & k‡nê ÂÆ ªV šÚ Z

·kÚæ:R Žçÿ& ®®B ·k Úæ® †Jš k² û

’² v®BÒ ®Æ, ·kÚæ:š šÚ ²Ê&r WO² Wš V

6 Ž"Ò®ê pretilt angleš k‡¶ n ÞÒ ²:. Z¢ ¢ z gn§‡ 6ÚæÒ ·k –® †û’² Êÿ®ê g†ûë

&ê 6Úæ & B¾r gn§ NOÊ gÆ& ®®B cycloid- dition n§š Ғr šÚ & ʇš 3‡®ê ë,^6-15 gÆ

² gn§‡ NO® ÚÊÒ v®ê ë, trans-cis gʇª ª Ò Êÿ®ê ë GÊ R² Êÿn6 Þ:.^16-18 N FÂ&rê poly- vinylcinnamate vÒ †û’² ÿ®B g†û’² ·k Úæ :Ê 6Úæ šÚ ²Ê&r †JÊ vnê ªÊî& V®B Æ

®6 g†ûr ·k® J e ±& V² †û žk‡š F®

V:.

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Ml0Fkxo#Olp*/#Vlh0K|xj#Fkrl*/#Zkdqnl#Nlp/#Vxqj#Vrr#Nlp/#dqg#Nljrrn#Vrqj^%# Materials Research Center for Information Display,

Kyung Hee University, Yongin, Gyeonggi-do 449-701, Korea

*LG.Philips LCD, Gumi 730-726, Korea (Received May 9, 2005;accepted June 1, 2005)

S¨Ü LCD †û’² §ÿ®† Z®B gn§‡ polyvinylcinnamate šÚ Z&r ·k Úæ:® †û& V² FÂÒ nß®V:. vg UVÒ polyvinylcinnamate šÚ& Îg®Ê v3WÎ gn§& ®®B šÚ & Ê‡Ê k‡n6,

šÚ ²Ê& Îg² ·k Úæê 6Úæ– ÚæZ Žçÿ’² 6Úæ †û ûR /Ò² û’² îv:. g†

ûš ÿ² ·k –® J e ±& V² žk‡– †û& UVÒ :2 Îg®6 Jš V²  vr ·k †û  ªÒ wk®B Æ®V:. vg UVÒ BBÞ Îg² šÚ®  î¢ Îg û& VÊ ²Û’² Îg²  g UV® û& †Ò ·k †ûÊ vn:./

Abstract:Orientations of liquid crystal molecules on a surface of a film of photoreactive polyvinylcinnamate were investigated in order to apply as an alignment layer of LCD. When the polyvinylcinnamate film was exposed to linearly polarized UV light, optical anisotropy was induced in the film through a selective photoreaction. Liquid crystal molecules on a surface of the film was aligned along the oriented polymer chain direction through intermolecular interactions.

Thermal and light stability of the photoaligned LC cell were studied by investigating LC alignment changes after the alignment layer was treated with heat and UV light. When the film was exposed with linearly polarized UV several times, the LC alignment was induced only along the final UV exposure direction.

Keywords: liquid crystal, alignment, photoreaction, stability, polyvinylcinnamate.

†To whom correspondence should be addressed. E-mail: [email protected]

2. /#

N FÂ&rê polyvinylcinnamate &>& fluorineÊ ®®r PVCN- FÒ ÿ®B 6Úæ g†ûš rÆ®V’Æ, Merck® ZLI-3449

·kš ÿ®B ·k –(LC cell)š rÆ®V:. PVCN-Fê mono- chlorobenzeneR dichloroethaneš 1:1² ’¿² ÿ:& ÏB 2 wt%®

ÿ·’² "6 , †f Z& 1800 rpm’² ú–ª[š ² :¢ 60 ×

² 30ÚZ ÊÆ2†:. PVCN-F šÚš 500 W high-pressure mercury lampÒ Êÿ®B 50 mW/cm² Ž†® UV WC ±’² gÆ®B

šÚ PVCN-F® gn§š v®VêÆ, vgÊ r UV ±Ê

šê¶ ê Glan-Taylor polarizerÒ ÿ®V:. PVCN-F šÚÊ ÛV ¦ r® v †fš 50 µm ¦.® çÊ ¢ÊZ² g¿®

B –š rƲ , ·kš þŽV þR(capillary effect)Ò Êÿ®B

– ² RÛ®V:. ·kš –& RÛ¶ ¢ê ^nê ·k †û

ûR n û’² RÛ®B þŽV þR& ®®B îö n Þê ·k †û þRÒ rÆ®V:.

50 µm – Zÿ® ·k –š ÿ² UV/Vis Úg :.&rê ·k

& ®² ·nV ^Š :r 250 nm&r V†nê ·k Úæ® ·n

’ÂÒ g wk¶ n :. NB² ·k® †ûš UV/Vis Úg :.’² V†®† Z®B ·kR tBr /Ү⠆J®ê Ê

‡ R"(dichroic dye) 1 wt%Ò ·k& ’¿®B –š rƲ  Ê

‡ R"® †ûš V†¾’²¾ ·k® †û ûš vê®V:.

N FÂ&rê 557 nm ·n’ÂÒ Vê ʇ R"Î methylene violetÒ ÿ®VêÆ, Úæ ÂÆ simulation Z²NþÎ HyperChem

š Êÿ®B š ² R methylene violet Úæ® ûëR transition dipole momentV Ê>ê WÊ 6°² Æ® ß®B UV/Vis Úg :.

RÒ ûë û’² Ês¶ n Þ:. UV/Vis Úg :.– Hitachi U-2000 double beam UV/Vis spectrometerÒ ÿ®V6, g UV/Vis Úg :.&rê sheet k2® vk gfš Êÿ®V:.

¦®ê ¦ gf Ê& Z®² šÚ Bê ·k –š ‚R®

B îzê ^ÊV® Ž†Ò wk®B 2"® g¯ ʇš wk®

V:. Uniphase® 10 mW He-Ne laser (632.8 nm), Oriel® Glan-Thomson

gfR Newport® 818-SL silicon detertorÒ ÿ®V6, silicon detector® 6Ž óCš ZÊ EG&G® trans-impedance preamplifier

– Hewlett-Packard® E3630A DC power supplyÒ ÿ®V’Æ, ‚ RÒ wk®B ʇš wk² :. û®® ‡š Figure 1& î

:.

3. ûG Z ë«

PVCN-F® UV Îg& †Î gn§ ª:î– Figure 2&r JE Ê 6Úæ & ïÞê cinnamoyl NOÊ [22] cycloaddition n

§š Ғúê ْ² ¢zŽ ÞêÆ,^8-10 ʖ o– 6Úæ ÂÆ®

ªV ·k Úæ:® †Jš k² û’² v®ê ÙÊ:.

vg UV ±š PVCN-F šÚ& Îg®Ê UV® g ûR  ß² cinnamoyl NO:– UVÒ ·n®B cycloaddition n§š Ғ

úê nÊ n’² Z®² cinnamoyl NO:– ±® ·nV z

" gn§š Ғú  – 2² þšÞâ r:. NB² gÆ

Z&ê G‡Ê® PVCN-F šÚ & gÆ& †Ò cinnamoyl NO ÚB® ʇ(anisotropy)Ê k‡r:. ·k:Ê PVCN-F šÚ Z&r vg UV ûR n’² †ûÊ vnê ٖ v3W

gn§& ®®B šÚ cinnamoyl NO® ÚBV UV– ß²  ûJ: n û& ª $Ê Ê®â nê 6Úæ šÚ® ʇ

¢ŽÊ:. PVCN-F šÚ ²Ê& Îg² ·k ÚæV van der Waals îR o– Úæ Ê® Žçÿ& ®®B 6Úæ® cinnamoyl NO R o– û’² îrâ r:. šÚ ²Ê& Îg®B Þ  –

·k Úæ: ·k Úæ: Ê Žçÿ& ®®B ²Ê&r v

’² þ6 ·k Úæ:Ê Îgr vg UV ûR n’² î rê ÙÊ:.

PVCN-F šÚ& vg UVÒ Îg®Æ šÚ & k‡nê g¯

ʇš Figure 1 :.û®Ò Êÿ®B wk®V:. vg UV ±

® g û& †Ò šÚ cinnamoyl NO:Ê v3WÎ gn Ê îîâ r:. šÚÊ G‡Ò ¢ê ^ÊV ªÊ r² n’

² ¦~r ¦ gfš R® ®:V šÚ & KÊ^Ê k

‡nÊ R®ê ^ÊV® Ž†V óV®², ÊÒ wk®B š Ú Ê‡ k‡ kÒ Æ®V:. vg UV Îg ^†&ê

polarizer

polarizer+.78µ, analyzer (- 45¶)

sample

detector mechanical chopper

controller lock-in Amp.

He-Ne laser

High pressure Hg lamp mechanical

chopper

polarizer

polarizer+.78µ, analyzer (- 45¶)

sample

detector mechanical chopper

controller lock-in Amp.

He-Ne laser

High pressure Hg lamp mechanical

chopper

Figure 1. Schematic diagram of the experimental set-up for film aniso- tropy measurements.

C O O

C O

O

C O O

C O

O

Direction of polarized UV

n F

F

F F

n n

n

Direction of LC alignment

Figure 2. [22] cycloaddition reaction model of PVCN-F.

PVCN-F šÚ® Ê‡Ê _ÿÞ óV®:V 100^Ò îrê Æ

ªV ê ٚ UV ÎgR /2& šÚ ‚RÒ wk² :.

RÎ Figure 3&r R n Þ:. ʖ o– ‚R wk Rê Î g UV® g û& V®B nR n’² WW :.®B 

 g UV/Vis Úg :. R– /Ò®V:. PVCN-F šÚ:&

V®B Îg UV ûR n e n’² WW – g UV/Vis ú ïR® cinnamoyl NO ’Â(272 nm) ·n® ~Ê(DßD]])Ò Î g 2Z& †Ò Figure 3& ²2®B ‚R :. R– š¦®

V:. g UV/Vis úïR® ·n ~Ê šÚ ‚R wk

R– /Ò®â Îg ^†& _ÿ®â óV²  ª Ê– š Ú& Ê‡Ê óV®  6 Òk² hš v®ê R²Ö†

šÚ ʇ® ªV cinnamoyl NO® ª& ®®B Ââ Wûqê ٚ «Î¶ n Þ:.

vg UVÒ Îg² PVCN-F šÚš †û’² ÿ®B ·k

–š rƲ  – ·k Úæ:® †J ûš g UV/Vis Úg :.’² wk®B Figure 3& šÚ& V² :. R– š¦®B Úæ :R Žçÿ& ®®B 6Úæ Ê v®ê û’

² †ûnêÆ, gÆr šÚš †û’² ÿ²  ·k–

UV Îg û& n’² †ûnÆ šÚ® Îg2Z& †Ò †û kV óV®ê ٚ –® ·n ~Ê(DßD]]) óV²Ö† ¢ n Þ:. Îg2Z& †Ò šÚ® ʇR N šÚš †û’²  ÿ² –® ʇ, ß ·k †û‡Ê oÊ óV®ê ٖ šÚ 6Úæ ® †ûÊ ·k® †ûš v²:ê ٚ ®N²:. ®

® †û ªV ^† gÆ  >‚ ¶Êâ Ê>ê ٚ R n ÞêÆ, Êê 6Úæ †û & Ê‡Ê Æ^" Ê®ªÒ

 ·k Úæ:– Ó⠆û® 6Úæ :Ê v®ê û’

² †Jn† ¢ŽÊ:.

g†û뒲 rƲ ·k –® J e ±& V² žk‡š Æ

®6æ g†ûr †û& UVÒ :2 Îg®6, Jš ª V®ê Figure 4® ÆÊ&r ·k †û® ªÒ Æ®V:. î¢(step 1)&

PVCN-F šÚ& vg UVÒ Îg²  šÚ k‡r 6Úæ®

ʇš wk®6, Ê šÚš †û’² ·k –š rÆ®B –

†ûR – ·k® †û û– g UV/Vis Úg :.&r WW

šÚ® cinnamoyl ’– – ʇ R" ’Â&r® ·nÒ wk®B Æ®VêÆ, Îg UV g ûš †V’² šÚ Bê

–š 10° "zVÆ wk®B Figure 5& W& †Î ·nÒ î

:. PVCN-F šÚ& î¢(step 1) vg UVÒ Îg² ê

Figure 4. Experimental conditions for the LC alignment stability test.

0.93 0.96 0.99

0

30

60

90

120

150 180

210 240 270

300 330

0.93

0.96

0.99

a)

2^nd 1^st

exposure direction

Step 1 Step 2 Step 3

0.3 0.6 0.9 1.2

0

30

60

90

120

150 180

210 240 270

300 330

0.3

0.6

0.9

1.2

b)

Step 1 Step 2 Step 3

Figure 5. Angular dependence of UV/Vis absorbance of (a) PVCN-F film ^maxQPDQGE/&FHOOZLWKGLFKURLFG\H^max557 nm).

(a)

(b) Figure 3. Changes in order parameter and transmittance of films and cell

with UV exposure time.

# 3# 433# 533# 633# 733# 833# 933# Exposure time(sec)

417 415 413 31;

319 317 315 313 [(AßAll)/(Aß+All)]

83#

73#

63#

53#

43#

3#

Transmittance(µV)

0 2 4 6 8 0 2 4

Film λ_max: 272 nm LC cell λ_max: 557 nm

UV ÎgR nÎ û 90°&r cinnamoyl ’ ·nV ²VÎ n Ê& ß² û 0°&rê ²âΠٚ Figure 5(a)&r R n Þ:.

Ê šÚš †û’² ÿ®B rƲ ·k – ® ·k †û

û šÚ® – /Ò®â Îg û& n’² îîê ٚ Figure 5(b)&r ¢ n Þ:. ·k †û® ±& V² žk‡–

Figure 4® step 1R step 2Ò þ¦ Ʋ PVCN-F šÚR Ê šÚš † û’² ÿ² ·k –® †ûš wk®B Æ®V:. î¢(step 1) gƲ PVCN-F šÚ& î¢ Îg ûR nÎ û’² v

g UVÒ :2 ÎgÊRÊ(step 2) î¢& k‡r šÚ cinnamoyl NO® ÚBV BҎ step 2&r Îg² UV û& nÎ û’

² cinnamoyl ’ Ž†V ²VV r:. Ê šÚš †û’² ÿ

² ·k –&r ²Û Îg û& n’² ·k® †ûÊ Ê>

Ž step 1&r 90°&r JÊ® ²V ·nV 15° ÖR’² „Š

ٚ Figure 5(b)&r R n Þ:. Step 2&r šÚ †û ûR ·k

ûÊ ÓZ ~ÊÒ JÊê ٖ step 1® Wûš šZ®â 

®V† ¢Ž’² Bþ:. ʖ oÊ FãW’² vg UVÒ Îg² &ê šÚ cinnamoyl NO® ÚBV  Îg&

VÊ ²Û’² Îgr g UV® û& n’² ª $Ê Ê

®â nÆ, N R ·k® †û 6Úæ ® cinnamoyl NO R® Žçÿ& ®®B ²Û UV Îg û& n’² †Jnê ÙÊ:. PVCN-F šÚ& vg UVÒ BB Þ(10â Ê) ã®B Îg¶ ¢ –n ÞNê Îgš 0° û&r N6 3n ÞN Îg

– –n ÞN– nÎ 90° û&r Þ^š VÆ ®Vš ¢& ´

® – oÊ Ã ²Û’² Îgr UV® û& n’² š Ú® cinnamoyl NOÊ $Ê Ê®V6 ·k ²Û UV Îg  û& n’² †ûÊ n:.

·k †û® J žk‡– gÆ(step1R step 2)² šÚš PVCN-F

® vZÊ~ 78 ×J: ÓZ – 70 ×&r 20ÚZ VJ®B (step 3) Æ®V:. šÚš vZÊ~ Ê’² VJ®Ê gÆ

² k‡r šÚ Ê‡Ê ZÖ Ò", gƲ šÚš step 3

® Æʒ² VJ î®Ê step 2&r v² šÚ Ê‡Ê N V² Ê®ê ÙÊ Figure 5(a)& JÎ:. ®" Ê šÚš †û’

² ÿ² ·k –&rê ·k® †û ûÊ šÚ cinnamoyl N O® †û ûR šZÞ :Êâ 50°² „Š ٚ R n Þ:. J î

 & šÚ® †û û– ®  ®êÆ – ·k® †û

ûÊ ² ٖ 6Úæ šÚ ²Ê&r® vZÊ~V bulk  2J: † ¢Ž& îò Z’² Bþ:.^19,20 †û&r ·k

†ûš :r² v®ê 6Úæê šÚ ²Ê& Ê®ê vZÊ

~V – :ʲ vZÊ~ ʮΠ70 ×&r šÚš

VJ®V šÚ ²Ê& Z®² :® †û– J ʚ(thermal relaxation)& ®Ê Òâ r:. ®" †û® VÖښ ~®

ê šÚ Ö® bulk 6Úæ:– VJ & †ûÊ vn², Ê Ê îîê ÙÊ:. šÚ ²Ê 6Úæ® †ûÊ  ʖ

o– šÚ’² ·k –š rÆ®Ê †û& ®² 0° û® ·k k‡r 90° û® flow effect& ®² NN² †û þRV îî g ZÎ 60° ÖR&r ·k® †ûÊ Ê>ê ْ² 3Wr:.

vg UV² Îg² PVCN-F šÚš †û’² ÿ² ·k

–š rÆ®B †Ê LCD Kk&r Êÿ®ê rubbing 뒲 rÆ

² PI šÚ †û® ·k –R Z†g¯ ‡š š¦®V:. 130

Hz® AC Z«š twisted nematic ·k –& ÎV®Æ gfš R

®B î~ ±® Ž†Ò Z«® Ž†& †Ò wk®V:. PI †ûš

rubbing² ·k –Êî g†û뒲 rƲ – þ¦ š ² Z†g

¯ ‡ RÒ Figure 6&r JBRêÆ, ÚZ«Ê 1.7 volt² î

’Æ ‚Rnê ±® Ž†V normally white modeî normally black mode&r þ¦ Æ ~ÊV Ê îî g†ûr PVCN-F šÚš

ÿ² ·k –Ê rubbingr †û® ·k –R /Ò² Z†g¯

‡š Vê ٚ ¢ n Þ:.

4. û«

gn§‡ 6ÚæÒ LCD® ·k †û Kk& Wÿ®† Z®B g Æ  6Úæ šÚ & k‡nê ÂÆ ª– ·k Úæ †û®

VVÒ Æ®V:. PVCN-Fê UV Îg& †Ò 6Úæ &

ïÞê cinnamoyl NOÊ [22] cycloaddition n§š Ғr ·k Úæ:® †ûš v®â r:. vg UVÒ PVCN-F šÚ& Îg

®Ê g ûR ß² cinnamoyl NO:– cycloaddition n§š

Ғr ê nÊ n’² Z®² NO:– gn§š Ғú

‡Ê k‡r:. šÚ ²Ê& Îg² ·k Úæê van der Waals î&

®®B 6Úæ® cinnamoyl NOR o– û’² îrâ n²

šÚ cinnamoyl NO †û ûÎ vg UV– n û’²

·kÊ †J®ê ÙÊ:.

g†ûš ÿ² ·k –® J e ±& V² žk‡š Æ®

6æ –& UVÒ :2 Îg®6 Jš V²  ·k †û ªÒ Æ

®V:. g UVÒ r² n®â ¦ Þ Îg² šÚ®  cin- namoyl NO® ÚBV  Îg& VÊ ²Û’² Îg²  g UV® û& n’² ª $Ê Ê®â nÆ, N R ·k®

†û ²Û UV Îg û& n’² î:. ·k †û® J ž k‡– gƲ šÚš PVCN-F vZÊ~J: ÓZ – ~

&r VJ®B Æ®V:. gÆr šÚš vZÊ~ Ê’

² VJ®Ê šÚ & k‡r Ê‡Ê ZÖ Ò" vZÊ

~J: ÓZ – ~&r VJ®Ê šÚ ʇ– NV² Ê®V:. ®" Ê šÚš †û’² ÿ² ·k –&rê

·k® †û ûÊ šÚ cinnamoyl NO® †û ûR šZÞ :Êâ îîêÆ, Êê 6Úæ šÚ ²Ê&r® vZÊ~V bulk 2J: † ¢Ž& îò Z’² Bþ:.

Figure 6. Electro-optical characteristics of twisted nematic LC cells.

0 0 0 0 0 0

Rubbing Photoalignment 130 Hz square wave, at 25 ^oC

Normally white mode

Normally black mode

433

;3 93 73 53 3

Transmittance(%)

318# 413# 418# 513# 518# 613# 618# Applied voltage(V)

[÷£ KÜN FÂê æ&Ö ~ŽVkJjúb^ʆvrr

> &(RrގAOD-3/F0004041)& ®®B nßn:.

ƒ+S

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