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液晶含量和外加电场类型是影响聚合物分散液晶薄膜电光性能的重要因素, 而对薄膜微观形貌的分析并不能直接反映电光性能的变化机理. 因此本文以液晶材料E7和光聚物NOA65共混制备的聚合物分散液晶薄膜作为研究对象, 通过对其极化特性的研究, 揭示了在不同液晶含量和不同类型电场下极化过程对薄膜电光性能的调控规律和微观机制. 结果表明, 在10–1—106 Hz频率范围内, 薄膜在低频、中频和高频存在3个松弛极化过程, 分别为热离子极化、界面极化和转向极化. 通过Arrhenius公式拟合计算了各极化过程的活化能, 发现随着液晶含量的增大, 转向极化的活化能从0.88 eV下降至0.83 eV, 导致液晶分子转向的阈值场强和饱和场强降低. 相比于交流电场, 直流电场下热离子极化形成内建电场, 导致阈值场强和饱和场强大幅增大, 而极化弛豫时间的延长会导致响应时间的延长. 此项研究对进一步分析和提升聚合物分散液晶薄膜的电光性能具有指导意义.The electro-optical properties of polymer dispersed liquid crystal film vary with liquid crystal content and externally applied electric field, but the analysis of the film morphology cannot directly reflect the mechanism of electro-optical properties. Therefore, the polymer dispersed liquid crystal film prepared by blending liquid crystal material E7 and photopolymer NOA65 is used. Herein, the dielectric polarization regulated electro-optical properties and their related mechanisms under different liquid crystal content and electric fields are revealed. The results show that in a frequency range of 10–1–106 Hz, the film exhibits three relaxation processes respectively at low frequency, medium frequency and high frequency, which are generated by thermionic polarization, interfacial polarization and orientation polarization. According to the Arrhenius equation, the activation energy values of such polarization processes are calculated. It is found that with the increase of liquid crystal content, the activation energy of orientation polarization decreases from 0.88 eV to 0.83 eV, leading the threshold field strength and the saturation field strength of the diversion of liquid crystal molecule to decrease. Thermionic polarization under DC electric field forms an internal electric field, which causes the threshold field strength and saturation field strength to increase greatly, as compared with the scenarios under AC electric field. Such a thermionic polarization also leads the polarization relaxation time to increase, resulting in the extension of response time. This study is of guiding significance in further analyzing and improving the electro-optical properties of polymer dispersed liquid crystal films.
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Keywords:
- dielectric relaxation /
- electro-optical property /
- polarization /
- relaxation time
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图 1 (a)电光性能测试和(b)介电性能测试的样品示意图
Fig. 1. Sample diagram of (a) electro-optical property test and (b) dielectric property test.
图 4 (a) 25 ℃和(b) –40 ℃下不同液晶含量PDLC薄膜的介电损耗谱
Fig. 4. Dielectric loss spectrum of PDLC films with different liquid crystal content at (a) 25 ℃ and (b) –40 ℃.
图 5 PDLC薄膜的极化活化能 (a) 50%, (b) 60%, (c) 70%和(d)极化活化能随液晶含量的变化趋势
Fig. 5. Polarization activation energy of PDLC films: (a) 50%, (b) 60%, (c) 70%, and (d) variation trend of polarization activation energy with liquid crystal content.
图 6 交流电场下, 不同液晶含量PDLC薄膜 (a)电场强度-透过率关系; (b)阈值场强和饱和场强
Fig. 6. (a) E-T relationship and (b) Eth and Esat of different liquid crystal content PDLC films under AC electric field.
图 7 直流电场和交流电场下PDLC薄膜的透过率对比图
Fig. 7. Transmittance comparison of PDLC films in DC and AC electric fields.
图 8 直流电场下, 不同液晶含量PDLC薄膜 (a)电场强度-透过率关系; (b)阈值场强和饱和场强
Fig. 8. (a) E-T relationship and (b) Eth and Esat of different liquid crystal content PDLC films under DC electric field.
图 9 (a)交流电场和(b)直流电场下PDLC薄膜的响应特性
Fig. 9. Response characteristics of PDLC films under (a) AC and (b) DC electric field.
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[1] Shen W B, Wang L, Zhong T J, Chen G, Li C X, Chen M, Zhang C H, Zhang L Y, Li K X, Yang Z, Yang H 2019 Polymer 160 53
Google Scholar
[2] Hu G, Chen H X, Liu Z Q, Zhang S, Zhou Y, Zhu B L, Gu H Z 2020 Liq. Cryst. 47 1582
Google Scholar
[3] Zhong T J, Mandle R J, Goodby J W, Zhang L Y, Zhang C H 2019 Polym. Adv. Technol. 30 2781
Google Scholar
[4] Li C X, Chen M, Shen W B, Chen G, Zhang L Y, Yang H 2019 Liq. Cryst. 46 1718
Google Scholar
[5] 聂永杰, 景钰, 张萌, 陈昊鹏, 赵现平, 赵腾飞, 项恩新, 王科, 鲁广昊, 朱远惟 2021 中国电力 54 144
Google Scholar
Nie Y J, Jing Y, Zhang M, Chen H P, Zhao X P, Zhao T F, Xiang E X, Wang K, Lu G H, Zhu Y W 2021 Electric Power 54 144
Google Scholar
[6] Nie Y J, Zhang M, Zhu Y W, Jing Y, Shi W L, Li G P, Chen H P, Jiang Y H, Zhao X P, Zhao T F, Lu G H, Li S T 2021 Materials 14 5901
Google Scholar
[7] 龙洁, 李九生 2021 70 074201
Google Scholar
Long J, Li J S 2021 Acta Phys. Sin. 70 074201
Google Scholar
[8] Hemaida A, Ghosh A, Sundaram S, Mallick T K 2020 Sol. Energy 195 185
Google Scholar
[9] 李文萃, 刘永刚, 宣丽 2011 60 046101
Google Scholar
Li W C, Liu Y G, Xuan L 2011 Acta Phys. Sin. 60 046101
Google Scholar
[10] Zhang W C, Fan D H, Gong Y L, Liang W L 2021 Liq. Cryst. 48 1643
Google Scholar
[11] Jiang J H, McGraw G, Ma R Q, Brown J, Yang D K 2017 Opt. Express 25 3327
Google Scholar
[12] Seo J, Nam S, Jeong J, Lee C, Kim H, Kim Y 2015 ACS Appl. Mater. Interfaces 7 504
Google Scholar
[13] Nasir N, Hong H R, Rehman M A, Kumar S, Seo Y 2020 RSC Adv. 10 32225
Google Scholar
[14] Meng X S, Li J, Lin Y Q, Liu X D, Zhao J W, Li D C, He Z H 2022 Crystals 12 163
Google Scholar
[15] Shi Z H, He Z M, Li C S, Miao Z C, Wang D, Luan Y, Li Y Z, Zhao Y Z 2022 Appl. Mater. Today 29 101622
Google Scholar
[16] Zhao Y Z, Li J Q, Yu Y, Zhao Y, Guo Z, Yao R J, Gao J J, Zhang Y M, Wang D 2022 Molecules 27 7265
Google Scholar
[17] 陈菲, 徐荣青, 李若舟, 严静 2018 液晶与显示 33 631
Google Scholar
Chen F, Xu R Q, Li R Z, Yan J 2018 Chin. J. Liq. Cryst. Disp. 33 631
Google Scholar
[18] Liang Z, Zhao Y Z, Gao H, Wang D, Miao Z C, Cao H, Yang Z, He W L 2021 Liq. Cryst. 48 2016
Google Scholar
[19] Nasir N, Kumar S, Kim M, Nguyen V, Suleman M, Park H M, Lee S, Kang D, Seo Y 2022 ACS Appl. Energy mater. 5 6986
Google Scholar
[20] Meng X S, Li J, Lin Y Q, Liu X D, Liu N N, Ye W J, Li D C, He Z H 2021 Liq. Cryst. 48 1791
Google Scholar
[21] Zhu Y W, Qiao N, Dong S Q, Qu G H, Chen Y, Lu W L, Qin Z Z, Li D F, Wu K N, Nie Y J, Liu B, Li S T, Lu G H 2022 Chem. Mater. 34 6505
Google Scholar
[22] 成鹏飞, 李盛涛, 李建英 2012 61 187302
Google Scholar
Cheng P F, Li S T, Li J Y 2012 Acta Phys. Sin. 61 187302
Google Scholar
[23] 李国倡, 李盛涛 2019 68 239401
Google Scholar
Li G C, Li S T 2019 Acta Phys. Sin. 68 239401
Google Scholar
[24] Li G C, Zhou X G, Li X J, Wei Y H, Hao C C, Li S T, Lei Q Q 2020 High Volt. 5 280
Google Scholar
[25] Yang J J, Wang Z C, Feng H, Wei Y H, Li G C, Zhu Y C, Hao C C, Lei Q Q, Li S T 2023 Ceram. Int. 49 14057
Google Scholar
[26] 李盛涛, 王辉, 林春江, 李建英 2013 62 087701
Google Scholar
Li S T, Wang H, Lin C J, Li J Y 2013 Acta Phys. Sin. 62 087701
Google Scholar
[27] Costa M R, Altafim R A C, Mammana A P 2001 Liq. Cryst. 28 1779
Google Scholar
[28] Islam R, Papathanassiou A N, Chan-Yu-King R, Roussel F 2016 Appl. Phys. Lett. 109 182901
Google Scholar
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