| 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.
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