紫外光固化时间对RAFT法制备的聚合物分散液晶膜电光性能及微观形貌的影响
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摘要
液晶/聚合物复合膜作为成膜材料,其紫外光固化时间对膜的电光性能及微观形貌有很大的影响。文中利用可逆加成-断裂转移自由基聚合(RAFT)制备了活性聚苯乙烯(PS)大分子引发剂,用以引发丙烯酸甲酯(MA)进行活性聚合制备聚合物分散液晶(PDLC)薄膜。系统研究了紫外光固化时间对RAFT-PS基PDLC薄膜电光性能及微观形貌的影响及影响机理。研究表明,通过RAFT法制备的PDLC在较短时间内即完成相分离,并且随着紫外光固化时间的延长,PDLC的阈值电压(Vth)和饱和电压(Vsat)升高,关态透光率(Toff)、记忆效应(ΔT)和最大透光率(Tmax)下降,薄膜的微观形貌也出现了连续明显的变化。随着紫外固化反应时间延长,聚合物基体的相对分子质量显著增加。
UV curing time has a significant impact on the electro-optical properties and micro-morphology of polymer dispersed liquid crystals(PDLC) films used as liquid crystal/polymer composite materials. Polystyrene(PS) was synthesized through reversible additional-fragmental chain transfer(RAFT) polymerization and employed to initiate methyl acrylate(MA) until the polymer and liquid crystal were well phase separated. PDLC films were prepared by polymerization induced phase separation(PIPS). The effect of UV curing time on threshold voltage,saturate voltage,off-state transmittance,memory effect,maximum transmittance and micro-morphology of RAFT dependent PDLCs was studied systematically and the mechanism was also discussed. It is found that with increase of the curing time,the threshold voltage increases from 1V to 6. 5V,the saturate voltage increases from 11. 1V to 24. 1V,which can be contributed to increase of inter molecular forces between liquid crystals and polymer and the tightness of polymer network instead of insufficient movement capabilities of polymer chains. In addition,the off-state transmittance decreases from 19. 6% to 2. 2% because of a complete phase separation,while the maximum transmittance also decreasing from 77. 3% to 58. 5% can be contributed to the decline of matching degree of index between liquid crystals and polymer. The increase of curing time also leads to higher molecular weight,which means less memory effect.
UV curing time has a significant impact on the electro-optical properties and micro-morphology of polymer dispersed liquid crystals(PDLC) films used as liquid crystal/polymer composite materials. Polystyrene(PS) was synthesized through reversible additional-fragmental chain transfer(RAFT) polymerization and employed to initiate methyl acrylate(MA) until the polymer and liquid crystal were well phase separated. PDLC films were prepared by polymerization induced phase separation(PIPS). The effect of UV curing time on threshold voltage,saturate voltage,off-state transmittance,memory effect,maximum transmittance and micro-morphology of RAFT dependent PDLCs was studied systematically and the mechanism was also discussed. It is found that with increase of the curing time,the threshold voltage increases from 1V to 6. 5V,the saturate voltage increases from 11. 1V to 24. 1V,which can be contributed to increase of inter molecular forces between liquid crystals and polymer and the tightness of polymer network instead of insufficient movement capabilities of polymer chains. In addition,the off-state transmittance decreases from 19. 6% to 2. 2% because of a complete phase separation,while the maximum transmittance also decreasing from 77. 3% to 58. 5% can be contributed to the decline of matching degree of index between liquid crystals and polymer. The increase of curing time also leads to higher molecular weight,which means less memory effect.
引文
[1]黄子强.液晶显示原理[M].2nd ed.北京:国防工业出版社.2006:4-5.
[2]Skey J,O’Reilly R K.Facile one pot synthesis of a range of reversible addition–fragmentation chain transfer(RAFT)agents[J].Chem.Commun.,2008,35:4183-4185.
[3]Yamaguchi R,Sato S.Memory effects of light transmission properties in polymer-dispersed-liquid-crystal(PDLC)films[J].Jpn.J.Appl.Phys.,1991,30(2):616-618.
[4]Noh C H,Jung J E,Kim J Y,et al.A study on the morphology and electro-optic properties of liquid crystal-polymer composite films[J].Mol.Cryst.Liq.Cryst.,1993,237(1):299-309.
[5]Shimada E,Uchida,T.Control of polymer orientation in polymer dispersed liquid crystal(PDLC)[J].Jpn.J.Appl.Phy.,1992,31(2):352-354.
[6]Takatsji H,Takeuchi K,Umezu Y.A novel liquid crystal display:A rando mLy-oriented nematic liquid crystal display(RON-LCD)[J].Mol.Cryst.Liq.Cryst.,1993,225(1):81-88.
[7]Stannarius R,Crawford G P,Chien L C,et al.Nematic director orientation in a liquid-crystal-dispersed polymer:A deuterium nuclearmagnetic-resonance approach[J].J.Appl.Phys.,1991,70(1):135-143.
[8]He J,Yan B,Yu B Y,et al.The effect of molecular weight of polymer matrix on properties of polymer-dispersed liquid crystals[J].Eur.Polym.J.,2007,43(6):2745-2749.
[9]Nolan P,Tillin M,Coates D.High on-state clarity polymer dispersed liquid crystal films[J].Liq.Cryst.,1993,14(2):339-344.
[10]Maschke U,Conqueret X,Benmouna M.Electro-optical properties of polymer-dispersed liquid crystals[J].Macro mol.Rapid.Commun.,2002,23(3):159-170.
[11]Sugimura A,Ishino D.Nematic director deformation induced by a periodic surface anchoring strength[J].Thin Solid Films,2003,438-439:433-439.
[12]He J,Yan B,Wang X A,et al.A novel polymer dispersed liquid crystal film prepared by reversible addition fragmentation chain transfer polymerization[J].Eur.Polym.J.,2007,43(9):4037-4042.
[2]Skey J,O’Reilly R K.Facile one pot synthesis of a range of reversible addition–fragmentation chain transfer(RAFT)agents[J].Chem.Commun.,2008,35:4183-4185.
[3]Yamaguchi R,Sato S.Memory effects of light transmission properties in polymer-dispersed-liquid-crystal(PDLC)films[J].Jpn.J.Appl.Phys.,1991,30(2):616-618.
[4]Noh C H,Jung J E,Kim J Y,et al.A study on the morphology and electro-optic properties of liquid crystal-polymer composite films[J].Mol.Cryst.Liq.Cryst.,1993,237(1):299-309.
[5]Shimada E,Uchida,T.Control of polymer orientation in polymer dispersed liquid crystal(PDLC)[J].Jpn.J.Appl.Phy.,1992,31(2):352-354.
[6]Takatsji H,Takeuchi K,Umezu Y.A novel liquid crystal display:A rando mLy-oriented nematic liquid crystal display(RON-LCD)[J].Mol.Cryst.Liq.Cryst.,1993,225(1):81-88.
[7]Stannarius R,Crawford G P,Chien L C,et al.Nematic director orientation in a liquid-crystal-dispersed polymer:A deuterium nuclearmagnetic-resonance approach[J].J.Appl.Phys.,1991,70(1):135-143.
[8]He J,Yan B,Yu B Y,et al.The effect of molecular weight of polymer matrix on properties of polymer-dispersed liquid crystals[J].Eur.Polym.J.,2007,43(6):2745-2749.
[9]Nolan P,Tillin M,Coates D.High on-state clarity polymer dispersed liquid crystal films[J].Liq.Cryst.,1993,14(2):339-344.
[10]Maschke U,Conqueret X,Benmouna M.Electro-optical properties of polymer-dispersed liquid crystals[J].Macro mol.Rapid.Commun.,2002,23(3):159-170.
[11]Sugimura A,Ishino D.Nematic director deformation induced by a periodic surface anchoring strength[J].Thin Solid Films,2003,438-439:433-439.
[12]He J,Yan B,Wang X A,et al.A novel polymer dispersed liquid crystal film prepared by reversible addition fragmentation chain transfer polymerization[J].Eur.Polym.J.,2007,43(9):4037-4042.