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Impedance spectroscopy characteristics of nano ZnO doped liquid crystal/polymer film
Opto-Electronic Engineering 2020 Vol. 47 No. 9 190540
Article

Impedance spectroscopy characteristics of nano ZnO doped liquid crystal/polymer film

Funds: 

National Natural Science Foundation of China 61975122

Science and Technology Development Project of University of Shanghai for Science and Technology(USST) 36-17-302-041

DOI: 10.12086/oee.2020.190540
2020-9
2020 Vol. 47, No. 9
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    Abstract

  • Abstract

    In this paper, the electrical impedance spectroscopy characteristics of polymer dispersed liquid crystal (PDLC) doped with nano-zinc oxide rods and its sensing applications are studied. Polymer dispersed liquid crystal films have the characteristics of stable structure, resistance to mechanical impact and easy preparation. By doping nano-zinc oxide rods into the material, the sensing function of polar molecules such as ethanol gas can be realized through the analysis of electrical impedance spectroscopy. In this paper, the complex impedance spectra of thin films encountering ethanol molecules are studied and analyzed through comparative experiments. In addition, the electrochemical equivalent circuit was established and analyzed. It was found that the film could sensitively and effectively realize the sensing function of the ethanol molecules. The sensitivity and response time of the sensor are further analyzed and studied. The experimental study and analysis show that nano-zinc oxide rod doped PDLC film is expected to be used as a gas sensor for detecting polarity of ethanol and other materials. It has the advantages of high sensitivity, stable structure, high repeatability, and easy fabrication.

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  • 聚合物分散液晶材料(Polymer dispersed liquid crystal, PDLC)是液晶以微米量级的小微滴分散在有机固态聚合物基体内，形成一种液晶薄膜材料[]。最近的研究表明，向列型液晶材料也可应用于化学和生物制剂的可靠、低成本、便携式和高灵敏度的传感器[-]。Chang等人证明了液晶材料可用于检测有机气体。其中极性分子会引起液晶分子的取向排序发生转变[-]，此外，实验结果表明，当液晶材料吸收有机气体后反射出的光谱会发生红移现象[-]。对液晶进行纳米掺杂成为近年来研究的热点，掺杂材料由最初的无机纳米材料到纳米金属、纳米金属氧化物[-]。Lai等人将碳纳米管掺入液晶材料中作为化学气敏元件，用于检测甲基膦酸二甲酯(DMMP)[]以及丙酮极性气体[]，结果表明，经过纳米掺杂后，液晶材料对于气体的响应高出40%以上。纳米氧化锌(ZnO)具有优良的磁、光学、电和化学性能，对于乙醇、苯酚、一氧化氮、甲烷等极性分子也有着极高的传感特性[-]。其中，纳米氧化锌棒具有更高的表面体积比和有效电子禁带性质[-]，以及在接触极性气体后取向转动等特点使其在气体传感、聚合物涂层传感和光电探测等方面具有巨大的应用潜力[, -]。此外，有研究表明纳米ZnO棒在接触乙醇等还原气体时，氧原子会与还原气体发生反应，产生大量的电子，形成传导通道，导致电阻值发生很大变化[]。因此，通过检测电化学阻抗谱[-]中阻抗的变化，可以检测到乙醇气体。

    本文主要研究纳米ZnO棒掺杂聚合物分散液晶薄膜的电化学阻抗谱特性，分析了材料纳米形貌结构，通过测量复阻抗，得到电路分量值，将薄膜结构与电路元件进行等效拟合，建立等效电路，并进一步实验验证其实现传感功能的特点。实验表明，用纳米ZnO棒掺杂的聚合物分散液晶薄膜作为传感器件，具有易于制备，高灵敏度、响应快、重复性好等特点。

    将制备的PDLC材料加热至47 ℃，曝光固化后的液晶盒放置于恒温47 ℃的加热台上，使用玻璃棒将均匀加热后的PDLC材料从液晶盒的一侧缓慢滴入，利用毛细作用，使得材料均匀分布在液晶盒内。在实验中，环境温度维持在25 ℃~30 ℃，曝光光路如图 1(a)所示，激光波长为532 nm(光强度为22 mW/cm2)，激光器发出的光先经衰减片进行衰减，快门控制曝光时间，经透镜扩束为平行光，然后通过反射镜反射，平行光直接入射到曝光样品表面，进行1 min曝光，固化为PDLC薄膜。这是常用的PDLC薄膜制备方式：光致聚合相分离法[]。

    Figure 1. (a) Exposure optical path diagram of nano-ZnO rods doped PDLC film; (b) Liquid crystal cell silver paste copper wire connection diagram
    Figure  1.  Full-Size Img PowerPoint

    (a) Exposure optical path diagram of nano-ZnO rods doped PDLC film; (b) Liquid crystal cell silver paste copper wire connection diagram

    运用LCR测量仪时，为了达到方便并减小测量误差的目的，我们利用导电银浆和铜线粘连在液晶盒两端的ITO导电膜上，可使检测的数据会更加精准，如图 1(b)所示。

    表 1为制备纳米ZnO棒掺杂的PDLC以及纯净PDLC所需材料的质量百分比。

    本实验中，配置纳米掺杂的PDLC的材料体系包括向列液晶(99.9% TEB50+0.1% CB15的混合液晶，北京清华亚王液晶材料有限公司生产)；预聚物单体(EBECRYL8301，EB 8301，UCB公司生产)；交联剂(N-vinylpyrrolidone，NVP, Aldrich公司生产)；协引发剂(N-phenyl glycine，NPG, Aldrich公司生产)；光引发剂(Rose Bengal，RB，Aldrich公司生产)；表面活性剂(S-271POE Sorbitan Monoorate，S-271，ChemService公司生产)；纳米ZnO棒(所制备棒状材料直径范围为7 nm~10 nm，长度范围为120 nm~140 nm)。将混合物在避光条件下用超声乳化仪均匀混合，在暗室中静置24 h~48 h，制得所需的聚合物分散液晶材料。

    Sample LC/(wt%) NVP/(wt%) Doping material/(wt%) NPG/(wt%) Rb/(wt%) S-271/(wt%) EB8301/(wt%)
    ZnO-PDLC 34.76 9.94 0.1 0.4 0.15 9.94 44.71
    PDLC 34.76 9.94 \ 0.4 0.15 9.94 44.71
    CSV Show Table

    用万用表测量确定镀有氧化铟锡(ITO)导电层玻璃的正反面，将ITO面朝上放置。首先是ITO玻璃清洗：①碱性洗涤剂，50 ℃，30 min；②纯水，50 ℃，10 min；③纯水，50 ℃，10 min；④ 120 ℃烘箱，40 min烘干；⑤ UVO-Cleaner清洗，处理30 min，停机后等待5 min后取出样品。其次在喷射管内加半勺粉状间隔子(spacer，直径为20 μm)，在镀有ITO导电膜的玻璃基片喷射间隔子，将未喷涂spacer的ITO基片错开位置倒扣在喷涂过的样品上，控制1 cm2大小的正方形，通过真空包装机制成20 μm厚度的夹层。

    3.1   薄膜形貌

    图 2(a)为PDLC的SEM，图 2(b)为0.1 wt%纳米ZnO棒掺杂的PDLC的SEM图。SEM图像中无法观察到液晶微滴的存在，这是因为曝光聚合速度较快，引起PDLC膜中液晶微滴尺寸很小(小于1 μm)。对比发现，纳米ZnO棒掺杂的PDLC膜较纯净PDLC膜相比，分布均匀的聚合物网络状的结构更加清晰明显，这种现象是因为纳米ZnO棒的加入，影响液晶分子的扩散速度，使得聚合相分离过程速度减缓[-]。此外，有文献表明，ZnO纳米粒子会被液晶微滴以及聚合物基质捕获[-]，无法在SEM图中被显著观测到。

    Figure 2. (a) SEM diagrams of PDLC films; (b) SEM diagrams of nano-ZnO rods doped PDLC films
    Figure  2.  Full-Size Img PowerPoint

    (a) SEM diagrams of PDLC films; (b) SEM diagrams of nano-ZnO rods doped PDLC films

    3.2   纳米ZnO棒掺杂的PDLC阻抗特性及乙醇传感性能

    在低频(4 Hz~100 Hz)时，由于液晶界面处吸附大量离子，导致液晶性能下降。由于离子吸附速率与界面处离子浓度成比例，因此当频率足够高时，可以防止界面处产生大的离子浓度，从而可以减缓性能降低的速率；同时还观察到，在低频情况下，纳米ZnO棒掺杂的PDLC薄膜对乙醇的依赖性比较强烈。频率在104 Hz~107 Hz范围内时，阻抗呈线性衰减，相位角呈线性衰减并且接近-90°，因为乙醇对阻抗的影响基本为零，所以这纯粹是电容的电反应。

    Figure 4. Nyquist diagram of nano-ZnO rods doped PDLC films
    Figure  4.  Full-Size Img PowerPoint

    Nyquist diagram of nano-ZnO rods doped PDLC films

    复阻抗是评测电路、元件以及制作元件材料性能的重要参数，复阻抗Z通常定义为给定频率下对流经电路或元件的交流电流的抵抗能力，它用矢量平面上的复数表示。运用LCR测量仪，使用1 V的正弦电压信号和4 Hz至107 Hz范围内的频率来扫描测量薄膜的复阻抗(幅度和相位)。

    Figure 3. (a) Detection of phase angle and impedance-frequency relation of ethanol by nano-ZnO rods doped PDLC film; (b) Detection of phase angle and impedance-frequency relation of ethanol by PDLC film
    Figure  3.  Full-Size Img PowerPoint

    (a) Detection of phase angle and impedance-frequency relation of ethanol by nano-ZnO rods doped PDLC film; (b) Detection of phase angle and impedance-frequency relation of ethanol by PDLC film

    通过阻抗仪测量阻抗(Z)和阻抗相位角(θ)，基于所获得的实验数据，使用式(1)和式(2)计算复阻抗Z的实部Z'和虚部Z" []：

    图 4为纳米ZnO棒掺杂的聚合物分散液晶膜的奈奎斯特图，由图可知，奈奎斯特图的形状表明有两个不同的区域，则具有不同的涵义。在100 Hz至105 Hz频率范围内的阻抗，半圆形部分通常与通过电阻放电的电容器中的电荷有关。本文中半圆形部分是电阻与电容并联产生的，与PDLC薄膜存储电荷的能力有关。由图可以看出，只有一个容抗弧，即一个时间常数，时间常数实际上对应着特征频率，此处特征频率为104 Hz。同时，奈奎斯特图在4 Hz~100 Hz的低频范围内，也会出现一定斜率的直尾，这是由电极反应的反应物或产物的扩散控制。在该频率范围内，奈奎斯特图上直尾的斜率，即阻抗的相位，几乎保持不变。在两段频率范围内，这些结果与图 3(Bode图)所示的结果非常一致。

    Z′=Z√1+tan2θ,

    纳米ZnO棒掺杂的PDLC薄膜与纯PDLC薄膜的模量和相位测量值可以在波特图中表示，可以分析阻抗幅度和相位的趋势。图 3显示了两种薄膜在有无乙醇气体的情况下，测量的阻抗幅度和相位作为频率函数的实验数据。在检测有无乙醇气体的两种情况下，两种薄膜的阻抗结果趋势都相似，在通入乙醇气体时，存在电容位移行为，并且纳米ZnO棒掺杂的PDLC薄膜在低频情况下较纯PDLC薄膜变化更大。应归于纳米ZnO棒掺杂的PDLC薄膜检测有无乙醇气体的情况。并且图 3有助于为薄膜检测乙醇气体选择合适的频率响应范围。

    Z″

    3.3   等效电路模型分析

    综合以上两个频段，图 6为针对薄膜4 Hz至105 Hz频率的等效电路。该电路包括引线和电极中存在的电阻RS，双电层电容Cd(即本文中的薄膜作为电容器件), 以及代表自由电荷和偶极子迁移率的漏电阻Rd和一个串联的扩散元件CPE。

    等效电路元件Cd的大小与偶极极化有关，与薄膜是否检测到乙醇无关，在95%浓度的乙醇条件下，纳米ZnO棒掺杂的PDLC薄膜的电容性能会发生较小的变化。

    Figure 7. Experimental and simulated data of nano-ZnO rods doped PDLC films in the absence of ethanol
    Figure  7.  Full-Size Img PowerPoint

    Experimental and simulated data of nano-ZnO rods doped PDLC films in the absence of ethanol
    Figure 5. (a) Low-frequency equivalent circuits with frequencies ranging from 4 Hz to 100 Hz; (b) High-frequency equivalent circuits with frequencies ranging from 100 Hz to 105 Hz
    Figure  5.  Full-Size Img PowerPoint

    (a) Low-frequency equivalent circuits with frequencies ranging from 4 Hz to 100 Hz; (b) High-frequency equivalent circuits with frequencies ranging from 100 Hz to 105 Hz

    如图 5(a)为薄膜在低频情况下的等效电路，该电路包括一个由于偶极子位移而引起的电阻Rd和一个串联的扩散元件CPE，其等效电路的复阻抗Z可用式(3)描述。图 5(b)则表示薄膜在高频情况下的等效电路，该电路包括引线和电极中存在的电阻RS、双电层电容Cd(本文中的薄膜作为电容器件)、以及代表自由电荷和偶极子迁移率的电阻Rd(即漏电阻)，其等效电路的复阻抗Z可由式(4)描述[]：

    因此，电容Cd为0.41 F。然后利用ZView分析软件对纳米ZnO棒掺杂的PDLC薄膜电学特性进行拟合，将实验与模拟进行比较，从而验证所提出的等效电路。

    图 7为在无乙醇情况下，薄膜的频率-相位角与频率-阻抗关系的实验与拟合数据的波特图，此图验证了上文所提出的等效电路模型的合理性。但在高频区域出现的轻微差异，可能是由于用于PDLC测量的导线的电感所导致的。

    首先，对没有通入乙醇气体的薄膜进行拟合。在高频情况下，电容元件Cd相当于短路，RS的值等于高频极限情况下的阻抗值，该阻抗值为8.7 kΩ(参见图 3)。另一方面，在所选择的100 Hz~100 kHz的频率范围之内，当阻抗相位角接近-90°时，薄膜为纯电容状态，电容元件Cd为主要作用，可由下式计算：

    为了验证乙醇对纳米ZnO棒掺杂的PDLC薄膜的影响关系，研究一种电学等效电路。运用Randles等效电路模型，进行低频和高频范围建模拟合。

    基于薄膜在不同频率呈现不同结果的状况，两种等效电路必须包含整个频率范围。其中，ω为角频率，\omega {\rm{ = }}2{\rm{ \mathsf{ π} }}f(f为频率)；j为虚数单位，j2=-1；系数T和指数P是CPE的参数(图 5(a))，CPE的阻抗由两个参数来定义，即CPE-T(双电层电容)，CPE-P(弥散指数)，一般0 < P < 1。然而当P=1时，CPE表征为双电层电容T的电容响应。

    在高频(100 Hz~105 Hz)时，电容元件Cd相当于短路，则RS是电路中的主要影响因素。由于RS是电极端的电阻，所以在高频情况下，没有因为乙醇而发生明显的变化。乙醇并不会影响阻抗值的大小。在低频(4 Hz~100 Hz)时，Cd相当于开路，其阻抗值与开路时一样很高，所以影响阻抗值的主要为Rd，并且Rd的阻抗值与Nyquist图中半圆的直径有关，由于电荷转移或运动产生的电阻，Rd的阻抗值明显是因为乙醇极性分子的通入而发生改变。

    表 2显示了ZView软件根据等效电路拟合纳米ZnO棒掺杂的PDLC薄膜检测乙醇时各元件的拟合参数。这些结果与图 3波特图中报告的实验数据一致。

    Z|10<f<107=Rs+RP1+jωCdRP。

    等效电路元件Cd的大小与偶极极化有关，与薄膜是否检测到乙醇无关，在95%浓度的乙醇条件下，纳米ZnO棒掺杂的PDLC薄膜的电容性能发生较小的变化。另一方面，电阻Rd的值与奈奎斯特图中的半圆直径有关。由图 4所示，当薄膜检测到了95%浓度的乙醇极性气体时，乙醇与纳米ZnO发生还原反应，产生电子，导致电阻发生变化，半圆的直径减小，此时表 2中Rd的阻值也大幅度的减小。图 4中奈奎斯特图的直线尾部与CPE参数有关，其斜率取决于参数CPE-P，当薄膜检测到乙醇极性气体时，其斜率增加。在表 2中的CPE-P参数值中，可以反映这一特征。

    使用EIS频谱分析软件ZView将计算得到的实验数据与各种阻抗谱进行拟合。截取频率范围为4 Hz至105 Hz的阻抗作为阻抗谱拟合数据，在高频(100 Hz~105 Hz)时为纯电容行为；在低频(4 Hz~100 Hz)情况下，运用恒相位元素(CPE)来表征弥散效应。

    Z|10−1<f<10=Rd+1jωT−P，
    Figure 6. Equivalent circuits with frequencies ranging from 4 Hz to 105 Hz
    Figure  6.  Full-Size Img PowerPoint

    Equivalent circuits with frequencies ranging from 4 Hz to 105 Hz
    Concentration/(%) Parameter Value Error/(%)
    0 Rd/(MΩ) 0.45 1.43
    Cd/(nF) 0.41 3.26
    CPE-T 9.23×10-7 4.39
    CPE-P 0.47 3.81
    95 Rd/(MΩ) 0.03 1.49
    Cd/(nF) 0.48 1.92
    CPE-T 1.94×10-6 3.64
    CPE-P 0.57 1.56
    CSV Show Table

    在高频时，等效电路的RS元件是电路中的主要影响因素，在这些频率下，薄膜有无检测到乙醇，都不会导致阻抗的变化，因此，RS的大小与是否有乙醇无关。此外，为了分析薄膜检测到乙醇时的影响，在元件中添加了Cd参数。

    Cd=12π⋅f−90∘⋅|Z|−90∘。

    3.4   薄膜气敏特性

    RS=R0R1。
    Figure 8. Sensitivity of nano-ZnO rods doped PDLC and pure PDLC films to ethanol gas
    Figure  8.  Full-Size Img PowerPoint

    Sensitivity of nano-ZnO rods doped PDLC and pure PDLC films to ethanol gas

    基于纳米氧化锌棒掺杂的PDLC薄膜对乙醇气体中阻抗谱的变化，进一步研究纳米氧化锌掺杂的PDLC传感乙醇气体的灵敏度和响应时间等特性。

    通过对比图，观察到无掺杂的聚合物分散液晶薄膜的灵敏度，在不同频率下，对乙醇气体分子响应的灵敏度最大值为2.9。

    与之相反的，纳米ZnO棒掺杂的聚合物分散液晶薄膜在检测乙醇气体分子时，具有较高的灵敏度。在低频4 Hz~100 Hz左右，薄膜对乙醇气体的传感响应的灵敏度呈上升趋势，并在100 Hz左右，其数值高达14.3，灵敏度远远高于无任何掺杂的薄膜。但在高频100 Hz~106 Hz，其灵敏度呈快速下降趋势，并在104 Hz~106 Hz频率下，趋近于0。

    图 8分别为纳米ZnO棒掺杂与无纳米ZnO棒掺杂的PDLC薄膜在不同频率下，检测固定浓度的乙醇气体的灵敏度变化图。我们令通入0浓度乙醇气体的薄膜电阻为R0，令通入浓度为95%的乙醇的薄膜电阻为R1，则其相对灵敏度为[]

    Figure 9. Response-recovery curve of nano-ZnO rods doped PDLC to ethanol gas at 100 Hz
    Figure  9.  Full-Size Img PowerPoint

    Response-recovery curve of nano-ZnO rods doped PDLC to ethanol gas at 100 Hz

    使用LCR测量仪(IM3536A982-01，日本)，频率范围为4 Hz至107 Hz。在室温26 ℃下，测量不同频率下纳米ZnO棒掺杂的PDLC薄膜与纯PDLC薄膜通入乙醇气体前后的电阻值的变化。

    图 9为纳米ZnO棒掺杂的PDLC在频率为100 Hz时，其三次接触乙醇气体所获得的响应-恢复曲线。在19 s、131 s、250 s时通入乙醇气体，34 s、147 s、266 s快速撤出乙醇气体。通入乙醇气体后15 s的响应时间内，元件的阻抗曲线瞬间产生变化并急速下降；在撤出乙醇气体的瞬间，阻抗曲线瞬间响应并在4 s的恢复时间内迅速上升，三次分别恢复至50.18%、50.07%、51.11%，随后缓慢上升，但无法在短时间内恢复至最高值。关于纳米ZnO对乙醇的传感机制，其原理是ZnO与乙醇发生了还原反应，产生了电子，形成导电通道，导致电阻降低，这与孙社稷等人[]的解释一致，图 9表示的纳米ZnO棒掺杂的PDLC对乙醇气体的响应-恢复曲线也证明了这一点，可以看出电阻存在一个阶梯性的变化，因为材料发生了反应被消耗导致电阻逐渐减小。由此可以看出，本材料对乙醇气体极为敏感，响应快速，具有高灵敏度。

    本文制备了一种可用于检测乙醇等极性气体的新型纳米ZnO棒掺杂的聚合物分散液晶薄膜。通过测量薄膜阻抗，即可达到对乙醇等极性气体的传感目的。通过自制的PDLC薄膜器件，结合LCR测量仪，以乙醇作为被测物，对这种PDLC薄膜的性能进行了测试。研究了纳米ZnO棒掺杂的PDLC薄膜的气体检测及电学阻抗特性。薄膜在频率为100 Hz左右，环境温度为25 ℃时，对于乙醇极性气体的检测非常灵敏，灵敏度数值高达14.3。此外，薄膜检测传感的响应时间为15 s，且在4 s内阻抗便能迅速升至较高状态。同时，利用电化学阻抗谱以及ZView软件，建立电学等效电路模型，对薄膜的电化学阻抗谱进行模拟验证。实验与模拟结果都显示出该材料对乙醇这种极性分子极其敏感，因此，我们认为纳米ZnO棒掺杂的PDLC薄膜可作为传感器，在乙醇等极性气体分子检测领域具有重要的应用价值。

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    • Zhu Qing, qingz_sky@163.com On this SiteOn Google Scholar
      • School of Optical-Electrical and Computer Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China
      • Shanghai Key Lab of Modern Optical System, University of Shanghai for Science and Technology, Shanghai 200093, China
    • Liu Yourong On this SiteOn Google Scholar
      • School of Optical-Electrical and Computer Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China
      • Shanghai Key Lab of Modern Optical System, University of Shanghai for Science and Technology, Shanghai 200093, China
    • Jiang Zhipeng On this SiteOn Google Scholar
      • School of Optical-Electrical and Computer Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China
      • Shanghai Key Lab of Modern Optical System, University of Shanghai for Science and Technology, Shanghai 200093, China
    • Corresponding author: Zheng Jihong, jihongzheng@usst.edu.cn On this SiteOn Google Scholar

      Zheng Jihong, E-mail:jihongzheng@usst.edu.cn

      • School of Optical-Electrical and Computer Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China
      • Shanghai Key Lab of Modern Optical System, University of Shanghai for Science and Technology, Shanghai 200093, China
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    DOI: 10.12086/oee.2020.190540
    Cite this Article
    Zhu Qing, Liu Yourong, Jiang Zhipeng, Zheng Jihong. Impedance spectroscopy characteristics of nano ZnO doped liquid crystal/polymer film. Opto-Electronic Engineering 47, 190540 (2020). DOI: 10.12086/oee.2020.190540
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    • Received Date September 11, 2019
    • Revised Date January 02, 2020
    • Published Date September 14, 2020
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  • Sample LC/(wt%) NVP/(wt%) Doping material/(wt%) NPG/(wt%) Rb/(wt%) S-271/(wt%) EB8301/(wt%)
    ZnO-PDLC 34.76 9.94 0.1 0.4 0.15 9.94 44.71
    PDLC 34.76 9.94 \ 0.4 0.15 9.94 44.71
    View in article Downloads
  • Concentration/(%) Parameter Value Error/(%)
    0 Rd/(MΩ) 0.45 1.43
    Cd/(nF) 0.41 3.26
    CPE-T 9.23×10-7 4.39
    CPE-P 0.47 3.81
    95 Rd/(MΩ) 0.03 1.49
    Cd/(nF) 0.48 1.92
    CPE-T 1.94×10-6 3.64
    CPE-P 0.57 1.56
    View in article Downloads

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    Corresponding author: Zheng Jihong, jihongzheng@usst.edu.cn
    • 1.

      School of Optical-Electrical and Computer Engineering, University of Shanghai for Science and Technology, Shanghai 200093, China

    • 2.

      Shanghai Key Lab of Modern Optical System, University of Shanghai for Science and Technology, Shanghai 200093, China

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    Impedance spectroscopy characteristics of nano ZnO doped liquid crystal/polymer film
    • Figure  1

      (a) Exposure optical path diagram of nano-ZnO rods doped PDLC film; (b) Liquid crystal cell silver paste copper wire connection diagram

    • Figure  2

      (a) SEM diagrams of PDLC films; (b) SEM diagrams of nano-ZnO rods doped PDLC films

    • Figure  3

      (a) Detection of phase angle and impedance-frequency relation of ethanol by nano-ZnO rods doped PDLC film; (b) Detection of phase angle and impedance-frequency relation of ethanol by PDLC film

    • Figure  4

      Nyquist diagram of nano-ZnO rods doped PDLC films

    • Figure  5

      (a) Low-frequency equivalent circuits with frequencies ranging from 4 Hz to 100 Hz; (b) High-frequency equivalent circuits with frequencies ranging from 100 Hz to 105 Hz

    • Figure  6

      Equivalent circuits with frequencies ranging from 4 Hz to 105 Hz

    • Figure  7

      Experimental and simulated data of nano-ZnO rods doped PDLC films in the absence of ethanol

    • Figure  8

      Sensitivity of nano-ZnO rods doped PDLC and pure PDLC films to ethanol gas

    • Figure  9

      Response-recovery curve of nano-ZnO rods doped PDLC to ethanol gas at 100 Hz

    • Figure  1
    • Figure  2
    • Figure  3
    • Figure  4
    • Figure  5
    • Figure  6
    • Figure  7
    • Figure  8
    • Figure  9
    Impedance spectroscopy characteristics of nano ZnO doped liquid crystal/polymer film
    • Sample LC/(wt%) NVP/(wt%) Doping material/(wt%) NPG/(wt%) Rb/(wt%) S-271/(wt%) EB8301/(wt%)
      ZnO-PDLC 34.76 9.94 0.1 0.4 0.15 9.94 44.71
      PDLC 34.76 9.94 \ 0.4 0.15 9.94 44.71
    • Concentration/(%) Parameter Value Error/(%)
      0 Rd/(MΩ) 0.45 1.43
      Cd/(nF) 0.41 3.26
      CPE-T 9.23×10-7 4.39
      CPE-P 0.47 3.81
      95 Rd/(MΩ) 0.03 1.49
      Cd/(nF) 0.48 1.92
      CPE-T 1.94×10-6 3.64
      CPE-P 0.57 1.56
    • Table  1

      Theoretical percentage of PDLC materials prepared with a mass of 2 g

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    • Table  2

      The fitting parameters of the equivalent circuit components fitted by Zview

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