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Impedance spectroscopy characteristics of nano ZnO doped liquid crystal/polymer film
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摘要:
本文研究了采用纳米氧化锌棒掺杂的聚合物分散液晶(PDLC)的电阻抗谱特性及其传感应用。利用聚合物分散液晶薄膜具有稳固结构、能抵御机械冲击、容易制备等特点，在材料中掺杂纳米氧化锌棒，通过电阻抗谱性质分析，实现对极性分子如乙醇气体的传感功能。通过对比实验，研究分析了薄膜在遇到乙醇分子时的复阻抗谱的变化，并建立了电化学等效电路，发现该薄膜能有效地实现对乙醇分子的传感功能。并进一步分析研究了该检测传感的灵敏度和响应时间等特性。结果表明，以纳米氧化锌棒掺杂PDLC薄膜有望作为检测乙醇等极性的气体传感器，具有高灵敏度、结构稳定、重复性高、易于制造等优点。
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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Overview: 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. The design realizes the detection of ethanol by measuring the impedance change of the film. It does not need complicated optical instruments to analyze the spectra of polar gases, such as ethanol before and after passing through. The design is simple, practical, and real-time. Based on the liquid crystal cell coated with ITO conductive glass, nano-ZnO rod doped PDLC thin films were prepared by photopolymerization phase separation method. In this paper, the complex impedance spectra of thin films encountering ethanol molecules are studied and analyzed through comparative experiments. And the electrochemical equivalent circuit was established and analyzed. It was found that the film could sensitively and effectively realize the sensing function of ethanol molecules. The principle is that when nano-ZnO rods based on polymer dispersed liquid crystals are exposed to reducing gas ethanol, then oxygen atoms react with reducing gas to release electrons, thus forming conduction channels, which ultimately results in great changes in film impedance values. The sensitivity and response time of the sensor are further analyzed and studied. The impedance curve of nano-ZnO rod-doped PDLC changes instantaneously and drops sharply in the response time of 15 s after it is fed into ethanol gas at 100 Hz. Then in the instant of withdrawing ethanol gas, the impedance curve responds instantaneously and rises rapidly in the recovery time of 4 s. In addition, the experimental results show that the nano-ZnO films doped with 0.1% are very sensitive to the detection of ethanol polar gases when the frequency is about 100 Hz and the ambient temperature is 25 ℃. The sensitivity value is as high as 14.3. The sensitivity of PDLC films doped with nano-ZnO is much higher than that of films without any doping. Both experimental and simulation results show that the material is extremely sensitive to ethanol as a polar molecule. We believe that nano-ZnO rod doped PDLC films can be used as sensors and have important application value in the detection of polar molecules.
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图 1 (a) 纳米ZnO棒掺杂的PDLC薄膜制备的曝光光路图；(b)液晶盒银浆铜线连接制作图
Figure 1. (a) Exposure optical path diagram of nano-ZnO rods doped PDLC film; (b) Liquid crystal cell silver paste copper wire connection diagram
图 2 (a) PDLC薄膜的SEM图；(b)纳米ZnO棒掺杂的PDLC的SEM图
Figure 2. (a) SEM diagrams of PDLC films; (b) SEM diagrams of nano-ZnO rods doped PDLC films
图 3 (a) 纳米ZnO棒掺杂的PDLC薄膜检测乙醇的相位角及阻抗与频率关系的波特图；(b) PDLC薄膜检测乙醇的相位角及阻抗与频率关系的波特图
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
图 4 纳米ZnO棒掺杂的PDLC薄膜的奈奎斯特(Nyquist)图
Figure 4. Nyquist diagram of nano-ZnO rods doped PDLC films
图 5 (a) 频率范围为4 Hz至100 Hz的低频等效电路；(b)频率范围为100 Hz至105 Hz的高频等效电路
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
图 6 频率范围为4 Hz至105 Hz的等效电路
Figure 6. Equivalent circuits with frequencies ranging from 4 Hz to 105 Hz
图 7 纳米ZnO棒掺杂的PDLC薄膜在无乙醇情况下的实验数据与模拟数据
Figure 7. Experimental and simulated data of nano-ZnO rods doped PDLC films in the absence of ethanol
图 8 纳米ZnO棒掺杂的PDLC与纯PDLC薄膜对乙醇气体的响应灵敏度
Figure 8. Sensitivity of nano-ZnO rods doped PDLC and pure PDLC films to ethanol gas
图 9 100 Hz下纳米ZnO棒掺杂的PDLC对乙醇气体的响应-恢复曲线
Figure 9. Response-recovery curve of nano-ZnO rods doped PDLC to ethanol gas at 100 Hz
表 1 制备质量为2 g的掺杂PDLC材料的质量百分比
Table 1. Theoretical percentage of PDLC materials prepared with a mass of 2 g
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 
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表 2 Zview拟合的等效电路各元件的拟合参数值
Table 2. The fitting parameters of the equivalent circuit components fitted by Zview
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
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