【作者】 牛小玲；

【导师】 刘鹏； 刘卫国；

【作者基本信息】 陕西师范大学 ， 材料科学与工程， 2011， 博士

【摘要】 红外热释电探测器是利用材料的热释电效应探测红外辐射的器件,具有室温工作、广谱响应、不需偏压、功耗小、便携性好等优点。在热释电材料中,聚偏二氟乙烯(PVDF)及其共聚物是目前压电、热释电性能最好的有机材料。但在PVDF的四个结晶相中,具有最大自发极化的β相不能自然形成,限制了其应用范围。如何得到β相的PVDF成为人们研究的热点之一。另外,热释电探测器属于电学读出系统,存在需要复杂的电信号转换技术的支撑及灵敏度低的不足。因此,对于非电读出热探测器的研制显得极为迫切和必要。本论文以有机红外热探测材料为中心,着重对聚合物热释电材料—PVDF和非电读出机制的红外探测材料—液晶材料的热光性能进行了研究。采用溶液旋涂法制备了PVDF薄膜,通过改变热处理条件、溶剂的种类、极化电场,研究以上因素对PVDF结晶行为的影响。结果发现：缓慢冷却后的PVDF晶型以α相为主；冰水淬冷处理对PVDF薄膜β相的形成有利。60℃得到一定含量的β相PVDF,150℃处理主要得到了α相PVDF,而120℃热处理得到的主要为β相PVDF。以N,,N-二甲基甲酰胺(DMF)为溶剂制备的PVDF尊膜,比以二甲基亚砜(DMSO)、N,N-二甲基乙酰胺(DMAc)为溶剂所得PVDF薄膜的β相含量高。通过对极化前后PVDF薄膜的X-衍射(XRD)图谱分析,发现极化处理有利于PVDF的β相含量的提高。通过对不同热处理温度和极化后的PVDF薄膜的介电常数进行测试,发现极化后的PVDF薄膜的介电常数最高,其次是120℃热处理所得PVDF薄膜,介电常数较小是60℃和150℃热处理所得PVDF薄膜,说明经极化处理的PVDF薄膜和120℃处理36h,冰水淬冷的PVDF薄膜的极性较强,β相含量较高,进一步证实了IR和XRD的分析结果。PVDF的改性研究,一是采用高能紫外光辐照对PVDF进行改性。二是采用PMMA与PVDF共混改性的研究。结果发现：辐射照度的大小是影响PVDF晶型的主要因素,辐射时间对晶型改变的影响不明显。发现20 mw/cm2的照度处理几乎对样晶未产生任何影响。经照度为40、60 mw/cm2辐射后的PVDF,β相含量明显增加,而当照度达到80 mw/cm2后,所得PVDF以α相为主。即紫外辐射处理时照度为40、60 mw/cm2的辐射照度对PVDF的β相含量提高有利。PVDF与PMMA的共混可以提高PVDF中p相的含量,当PVDF/PMMA=70/30时,共混物中PVDF的β相含量较高,结晶度较大。以上改性方法的优点为设备简单,原料廉价,制备方便。为提高PVDF的铁电性能提供了新的研究方法。对在铁电液晶制备方面起重要作用的手性化合物S811的热力学、电学性能进行了研究。结果发现：S811的热释电潜中,在其相变温度附近出现了较强的热释电电流峰。同样,在S811的介电温谱中,在相变点附近出现了介电常数的突跃。这符合电介质发生相变或其他结构的微观上的变化时,介电常数将会出现异常的理论。S811的介电损牦值较小。另外,S811冷却过程中,在其相变前后,出现了双电滞回线,证明它是类似于反铁电体的材料。与无机热释电材料相比,虽然S811热释电系数P不是很大,但是其介电常数(ε)及介电损耗(tan6)均较小,导致其优值因子Fv、Fd值比较大,具有热释电探测应用的潜力。为了研制光学读出的红外探测器,研究了液晶小分子的折射率-温度变化关系。另外,为了改善液晶的成膜性能,采用热引发法,以甲基丙烯酸甲酯(MMA)和液晶材料(5CB)为主要原料,制备了聚合物与液晶不同比例的聚合物分散液晶(PDLC)和聚合物网络液晶(PNLC)薄膜,并对它们的结构、热光、电光效应进行了研究。结果表明：5CB、HHV液晶的折射率是温度的灵敏函数。通过DSC、POM分析发现液晶含量为30%的PDLC薄膜的分散性较好。利用椭偏仪建模分析得出30%的PDLC薄膜的热光系数较大,PDLC薄膜的电光性能测试结果发现该薄膜还具有较强的电光效应。PNLC薄膜的热光性能不及液晶小分子。当MMA含量为7%时所制备的PNLC薄膜的电光性能较佳。以液晶的旋光效应为理论基础,设计了一种非电读出的红外热成像光学系统。该系统与电学读出红外探测系统相比,具有设备小、成像方式简单、精度高等优点。针对该系统的研制,着重研究了胆甾液晶和扭曲向列相液晶的旋光度—温度变化的关系,并设计了一种旋光度—温度关系测量的光学系统。结果发现：这两种液晶的旋光度随温度呈线性变化,旋光度—温度变化率为2 Lux/℃左右。通过CCD形象化地证明了液晶旋光度随温度的灵敏变化的关系。另外,通过微囊化技术对液晶进行微囊化处理,改善其成膜性。在微囊处理中温度、pH值等因素对液晶的微囊化影响很大。以上有关液晶热光效应的研究,为其在非电读出红外探测器方面的应用提供了实验基础。更多还原

【Abstract】 The devices of pyroelectric infrared detectors are based on materials pyroelectric effect to detect infrared radiation. They have the following advantages: working at room temperature, broad-spectrum response, no bias, low power consumption, portability. Among the pyroelectric materials, polyvinylidene fluoride (PVDF) and its copolymers possess excellent piezoelectric, pyroelectric properties. However, in the four crystalline phase of PVDF, theβphase with largest spontaneous polarization can not be formed naturally. The applications of PVDF are limited greatly. How to getβphase of PVDF film has become a subject for active research in the recent years. On the other hand, the pyroelectric infrared detectors belong to electrical readout system. They have the shortcomings of needing for complex electrical signal conversion technology and low sensitivity. Therefore, the research on non-electrical readout system of infrared detector is urgent and necessary. In this paper, we studied on the organic thermal detection materials:PVDF and liquid crystals respectively.The PVDF films were prepared by spin-coating solution method. The crystallization behaviors of PVDF were investigated by changing process temperature, solvent polarity and poling conditions. The results showed that the PVDF films of slow cooling treatment were a phase mainly, and ice water quenching treatment was favorable to the formation of (3 phase. The a phase PVDF film was obtained by ice water quenching treatment at 150℃. After 120℃quench treating, PVDF film was (3 phase mainly. There was a small amount ofβphase in PVDF film at 60℃. The crystallization behavior of PVDF films was influenced significantly by different solvent:DMSO, DMF, DMAc. Among them, choosing DMF as solvent, the content ofβ-phase in PVDF films was higher. After analyzing the XRD patterns of poled and unpoled PVDF films, we found that the poling process enhance theβ-phase diffraction intensity. The dielectric constants of PVDF films with different treatment condition were tested. The dielectric constant was closely related to the polarity of PVDF. The dielectric constant and the content of P-phase were investigated. The dielectric constant results were consistent with those of IR and XRD.On the modification of PVDF, firstly, high-energy ultraviolet light was used for modifing the PVDF films. Secondly, PMMA/PVDF blends were prepared by changing their mass ratios. The results showed that the UV radiant illuminations were found to induce the changes of PVFD films about the physical, chemical, thermal, structural respects in the range of 20～80 mW/cm2. The radiation time had little effect on the PVDF films. With 40、60 mw/cm2 radiant illuminations, theβphase constent was increased significantly, The PVDF film wasαphase mainly with 80 mW/cm2 radiation. The results of PMMA/PVDF blends showed that the PMMA content of blend had evident influence onβ-Phase crystal formation of PVDF. The blend film of PMMA /PVDF=30/70 had the highest PVDFβ-Phase content. The above methods have the advantages of simple, low cost and easy preparation, and are useful for enhance the ferroelectric properties of PVDF.The chiral dopant:(S)-(+)-4-{[(1-methylheptyl)oxy]carbonyl}phenyl-4-(hexyloxy) benzoate(S811) plays a major role in the preparation of ferroelectric liquid crystal. It was discovered exhibiting anti-ferroelectric and large pyroelectric behaviors near the phase transition. The electrical properties and thermodynamic behaviors of S811 had been investigated by pyroelectric, dielectric, polarization spectroscopy and DSC, PLM at different temperature. There was a sharp growth of dielectric constants at the phase transition temperture. Although the pyroelectric coefficient of S811 was low, but the figures of merit:Fv and Fd were large because of the low values of dielectric constant (ε’) and dielectric loss values (tanδ). The outstanding pyroelectric performances of S811 made it possible as a novel pyroelectric material.In order to develop an optical readout infrared detector, the liquid crystal refractive index dependence of temperature was studied. To improve the liquid crystal film-forming property, the Poly (methyl methacrylate)-based polymer dispersed liquid crystal (PDLC) and polymer network liquid crystal (PNLC) materials were prepared by the method of thermal initiation by different 5CB and MMA mass ratios. The structures, thermo-optical, electrical-optical properties of PDLC and PNLC films were characterized. The results showed that when the liquid crystal (LC) 5CB was 30 percent in PDLC, the dispersed states of LC was well-proportioned, the variation of transmittance and thermo—optical coefficient were the largest. In the PNLC films, when the MMA was 7 percent, the thermo-and electrical optical properties were better.Based on the optical rotation effect of liquid crystal, a non-electrical readout system of infrared imaging was developed. Comparing with electrical readout system, the system was accuracy, simple, small equipment and so on. Another optical system was developed for studying on the relationships between the liquid crystal optical rotation vs temperature. In order to visualize the liquid crystal optical rotation and temperature relationships, we used a charge coupled device (CCD) camera to record the light intensity changes in the heating process. The results showed that the optical rotation of two kinds of liquid crystals:cholesteric liquid crystal and twisted nematic liquid crystal were very sensitive to temperature. Lastly, we improved the liquid crystal film-forming by the treatment of miro-encapsulated the liquid crystal. Through many times experiments, we found that temperature and pH were main influence factors in the micro-encapsulation process. The above studies provide experiment bases for the liquid crystal materials using in the application of non electrical readout infrared detectors.更多还原