低阈值电压柔性PDLC膜电光特性的研究

研究了以ITO-PET为基板柔性PDLC膜的电光特性,讨论了基板的表面效应、单体的黏度、膜厚、单体的含量等因素对PDLC膜电光特性的影响.研究发现,在相分离的过程中,与表面摩擦方向近似相互垂直的上下两柔性基板上的摩擦印痕边界之间易形成类似于槽栅状聚合物"壁垒".这些聚合物"壁垒"具有很强的表面锚定能,能固定液晶微滴,阻止其流动和相互之间团聚,使得细小液晶微滴能按照摩擦方向排列整齐,可以降低其阈值电压和饱和驱动电压,且提高了对比度.研究还发现单体与液晶二者之间黏度的匹配程度也是实现优异电光性能的关键因素之一.通过优化不同膜厚和单体的含量,制备出了具有低阈值电压、低饱和驱动电压、较高对比度的柔性PDLC膜.     

聚合物分散液晶膜的制备及电光性能

采用紫外光聚合相分离(PIPS)法制备聚合物分散液晶(PDLC)薄膜,使其在断电状态下具有高的散射性而在通电后又具有高的透过率。实验通过改变液晶/预聚物复合体系中活性稀释剂单体的种类、单体与树脂的比例来调控聚合物与液晶微滴界面的锚定能,以改善PDLC的电光特性。研究了不同种类的活性稀释剂单体、树脂与单体比例对PDLC膜的偏光显微镜下形貌、光电性能的影响。最后优化工艺参数,制备出低阈值、高对比度的PDLC薄膜。实验结果表明,采用单体甲基丙烯酸月桂酯(LM)与聚酯类树脂5034的混合物与液晶混合,经相分离得到的PDLC膜在断电状态下具有高的散射性而且通电时有高的透过率,驱动电压低,对比度高。     

交流电场促进相分离法制备聚合物分散液晶

在单体与液晶相分离的过程以及单体固化的过程中施加交流电，得到液晶微滴尺寸和排列规则的PDLC膜。采用偏振红外光谱法对电场作用下液晶分子的重新取向进行了研究。结果表明：非工作状态下，液晶微滴的分子光轴处于无序态；工作状态下，分子光轴能够达到较高的有向度。     

聚合物分散液晶的相行为

针对聚合物分散液晶(PDLC)二元体系进行了研究，主要包括外加直流电场下制备的PDLC的相图研究以及PDLC形成过程中相分离情况。在PDLC制备过程中由于外加直流电场对小分子液晶的作用，使液晶在此二元结构中的清亮点发生变化。结果表明，直流电场的引入导致PDLC中液晶清亮点升高。相分离行为主要是跟踪PDLC形成过程中由于小分子液晶与高分子链段之间的排斥作用而引起的相分离，研究了不同条件下PDLC相分离的快慢。     

大分子引发剂和交联剂对PDLC电光性能的影响

采用反向原子转移自由基聚合制备苯乙烯引转移终止剂活性大分子(MI),并通过光聚合诱导相分离法制备聚合物分散液晶(PDLC)膜,研究了MI含量和交联剂(HDDA)的含量对PDLC开态透光率、阈值电压(Vth)、饱和电压(Vsat)、记忆效应和对比度的影响。结果表明,当PDLC中的MI含量从5%增到10%时,开态透光率增加,而阈值电压(Vth)、饱和电压(Vsat)降低,记忆效应增强,对比度先增加,然后又降低;当PDLC中的HDDA含量从25%增加到90%时,开态透光率降低,Vth、Vsat增加,记忆效应减弱。     

紫外光固化时间对RAFT法制备的聚合物分散液晶膜电光性能及微观形貌的影响

液晶/聚合物复合膜作为成膜材料,其紫外光固化时间对膜的电光性能及微观形貌有很大的影响。文中利用可逆加成-断裂转移自由基聚合(RAFT)制备了活性聚苯乙烯(PS)大分子引发剂,用以引发丙烯酸甲酯(MA)进行活性聚合制备聚合物分散液晶(PDLC)薄膜。系统研究了紫外光固化时间对RAFT-PS基PDLC薄膜电光性能及微观形貌的影响及影响机理。研究表明,通过RAFT法制备的PDLC在较短时间内即完成相分离,并且随着紫外光固化时间的延长,PDLC的阈值电压(Vth)和饱和电压(Vsat)升高,关态透光率(Toff)、记忆效应(ΔT)和最大透光率(Tmax)下降,薄膜的微观形貌也出现了连续明显的变化。随着紫外固化反应时间延长,聚合物基体的相对分子质量显著增加。     

溶剂法制备聚合物分散液晶膜

用溶剂法制备了聚合物分散液晶膜。采用偏光显微镜、扫描电子显微镜和电光仪对相分离和聚合物分散液晶材料的电光性能作了初步探讨。研究结果表明，升温速度和聚合物含量对PDLC膜的相分离结构和响应电压有显著的影响。     

大分子链转移剂活性对聚合物分散液晶电光性能的影响

采用可逆加成-断裂链转移(RAFT)、引发转移终止(Iniferter)、反向原子转移自由基聚合(RATRP)等活性自由基聚合方法,合成了分子量相近而带有不同端基的大分子链转移剂。通过紫外光聚合诱导相分离法制备聚合物分散液晶(PDLC)膜。通过研究大分子链转移剂光引发活性,发现采用RAFT聚合制备的大分子链转移剂具有较高的光活性,带有Iniferter活性基团的大分子链转移剂光活性很低。对不同大分子链转移剂制备的PDLC膜的电光性能进行比较,发现采用RAFT法合成的具有高光活性的大分子链转移剂能够使PDLC膜具有较高的开态透光率和较低的驱动电压。加入大分子链转移剂会导致PDLC记忆效应升高。     

超支化预聚物的合成及对聚合物分散液晶膜电光性能的影响

聚合物基体对聚合物分散液晶(PDLC)膜电光性能影响很大。文中,用不同比例单乙烯基和二乙烯基单体通过可逆加成-断裂链转移自由基聚合(RAFT)得到了一系列超支化聚合物。这些超支化聚合物可作为"活性"预聚物用于聚合诱导相分离(PIPS)来制备超支化树脂基PDLC膜。结果表明,添加不同预聚物导致不同的表面形貌,进而影响到阈值电压大小。驱动电压对聚合物基体分子量有一定的依赖性,分子量高的基体驱动电压相对较高。此外,滞后和记忆效应随基体支化度提高而减小,这可能与超支化结构增强了聚合物与液晶间的相互作用力有关。     

微接触区中边界膜滑移效应分析:微接触区宽度和表面粗糙度的影响

分析研究了微接触区宽度和表面粗糙度对微接触区中边界膜滑移效应的影响。微接触属混合接触,微接触区由边界膜区和传统流体膜区组成。当膜厚较大时,这里边界膜可看成纳米级薄膜。边界膜滑移由较大载荷下边界膜区大的压力梯度引起,在两接触表面同时发生。研究结果表明,微接触区宽度的增大使边界膜滑移效应增强,而表面粗糙度增大使边界膜滑移效应减弱甚至可使边界膜不发生滑移。边界膜滑移对微接触性能的影响是:边界膜滑移使通过微接触区的流体流量明显增大,使微接触区的承载能力减小,使微接触区局部压力降低。当边界膜厚度处于1nm量级时,微接触性能分析应考虑边界膜滑移效应,因为此时边界膜滑移可显著降低微接触区局部压力,考虑到实际接触表面为弹性表面,这种压力降低可显著改变接触表面弹性变形量进而影响微接触区的局部膜厚。     

Gradient polymer-disposed liquid crystal single layer of large nematic droplets for modulation of laser light

The light modulating ability of gradient polymer-disposed liquid crystal (PDLC) single layer of large droplets formed by nematic E7 in UV-cured polymer NOA65 is studied. Operating at relatively low voltages, such PDLC film with a of thickness 10-25?μm and droplet size up to 50?μm exhibits a good contrast ratio and is capable of producing a large phase shift for the propagating coherent light. For a linearly polarized He-Ne laser (λ=633?nm), an electrically commanded phase shift as large as π/2 can be obtained by the large-droplet region of the film. The electrically produced phase shift and its spatial profile controlled by the thickness of the gradient PDLC single layers of large nematic droplets can be useful for tunable spatial light modulators and other devices for active control of laser light.     

Polarization-independent optical fiber modulator by use of polymer-dispersed liquid crystals

Ultrasmall light modulators have been made by sandwiching a polymer-dispersed liquid crystal (PDLC) between two ferrules with optical fibers. The device can modulate light independent of the state of polarization, because the PDLC becomes transparent or opaque when either sufficient or no voltage is applied to the film. The PDLC was prepared by mixing and annealing a prepolymer and nematic liquid crystal with large anisotropy. An optical fiber modulator with a 30-mum thick PDLC film had an extinction ratio of 8:1-33:1, an insertion loss of 1.3 dB, and rise and decay times of 4 ms at a wavelength of 1.3 mum.     

Droplet orientation and optical properties of polymer dispersed liquid crystal composite films

The electro-optic and thermo-optic properties of polymer dispersed liquid crystal (PDLC) films have been investigated. The effects of applied voltage and temperature on liquid crystal droplet morphology and its transmission characteristics were studied. Threshold voltage (V_th) and optical transmission increases with increasing temperature. It may be due to the reduction in effective voltage drop across the liquid crystal droplets in the composite matrix. The liquid crystal droplet size was found to vary in the range of 5–28 μm.     

高度支化水性聚氨酯的合成及性能EI

以甲苯-2,4-二异氰酸酯(TDI)、聚碳酸酯二醇(PCDL)、二羟甲基丙酸(DMPA)和聚醚胺(ATA)为原料,采用A2+B3法合成了具有高度支化结构的水性聚氨酯(HBAPU)乳液。用红外光谱(FT-IR)对产物结构进行表征;用光子相关光谱(PCS)研究了乳液的稳定性能,NCO/OH=1.3,w(DMPA)=6%时可以得到稳定的HBAPU乳液;采用旋转黏度计、差式扫描量热仪(DSC)、热失重分析仪(TG)、电子拉力机对产物的流变行为和各种性能进行了测试。结果表明,相对于线性水性聚氨酯(LAPU),HBAPU产物具有较低的黏度、良好的热稳定性、较高的Tg和拉伸强度。     

Optical transmission of polymer dispersed liquid crystals doped with carbon nanotubes

The optical transmission of polymer-dispersed liquid crystals (PDLCs) doped with multiwall carbon nanotubes (MWNTs) has been studied in comparison to the analogous system without MWNTs. The transmission of MWNT-doped PDLC cells in crossed polarizers exhibits an anomalous dependence on the control voltage. The anomalous behavior is attributed to a preliminary partial orientation of molecules in the presence of carbon nanotubes in the dispersed liquid crystal droplets.     

Investigation of nonionic diazo dye-doped polymer dispersed liquid crystal film

Sudan black B (SBB) was used to investigate as the nonionic diazo dye-doped in polymer dispersed liquid crystal (PDLC) display, by polymerization-induced phase separation (PIPS) method. The maximum absorbance, contrast ratio, dichroic ratio and the order parameter of nonionic diazo dye in nemetic host (TL203) were investigated using UV?CVis polarized spectroscopy. The orientation of the dye molecules was controlled by electric field, which enabled the contrast ratio of the dye to be obtained by electrically switching. The change occurring on droplet morphologies and electro-optical properties of PDLC film with the change in contents of Sudan black dye and liquid crystals (LC) contents was investigated. We found an increase in LC droplet sizes with the increase of diazo dye and LC contents. Moreover the addition of small amount of nonionic diazo dye reduced the threshold voltage (V $_{\boldsymbol{\rm th}})$ , increased off-state transmittance, enhanced the contrast ratio and decreased the response time of dye-doped PDLC. Additionally the change in transition temperature of LC and changes in LC droplet morphologies with the addition of dye were also observed. Such changes were observed with the images taken by polarized optical microscope (POM). The detail discussions on such behaviours were also made.     

Advances in the display quality of dye-doped polymer-dispersed liquid crystal films by addition of disc-shaped multidirectional light-control film

Typically, the addition of a dye is considered to increase the contrast ratio (CR) of a polymer-dispersed liquid crystal (PDLC) display; however, with the addition of a small amount of dye, the contrast ratio (CR) unexpectedly decreased as compare to the CR of a normal white PDLC display, attributed to various reasons. In this study, an additional multidirectional light scattering polymer film is developed over a conventional dye-doped polymer-dispersed liquid crystal (DPDLC) film to enhance the CR. For this, a disc-shape (DS) pattern on PN393 film is coated. This structure is believed to enhance the scattering properties of DPDLC displays via multiple-directional scattering nature of DS pattern film. Fabrications of such devices are simple and have advantageous of its low-cost production. This optimal designed disc-shaped light-scattering (DSS) film resulted in the enhancement of the CR of the DPDLCs.     

Fabrication of flexible polymer dispersed liquid crystal films using conducting polymer thin films as the driving electrodes

Conducting polymers exhibit good mechanical and interfacial compatibility with plastic substrates. We prepared an optimized coating formulation based on poly(3,4-ethylenedioxythiophene) (PEDOT) and 3-(trimethoxysilyl)propyl acrylate and fabricated a transparent electrode on poly(ethylene terephthalate) (PET) substrate. The surface resistances and transmittance of the prepared thin films were 500-600 Ω/□ and 87% at 500 nm, respectively. To evaluate the performance of the conducting polymer electrode, we fabricated a five-layer flexible polymer-dispersed liquid crystal (PDLC) device as a PET-PEDOT-PDLC-PEDOT-PET flexible film. The prepared PDLC device exhibited a low driving voltage (15 VAC), high contrast ratio (60:1), and high transmittance in the ON state (60%), characteristics that are comparable with those of conventional PDLC film based on indium tin oxide electrodes. The fabrication of conducting polymer thin films as the driving electrodes in this study showed that such films can be used as a substitute for an indium tin oxide electrode, which further enhances the flexibility of PDLC film.