Kinetics investigations for holographic Bragg grating based on polymer dispersed liquid crystal

This paper investigates the monomer kinetics of polymer dispersed liquid crystal （PDLC） grating. Fourier transform infrared （FTIR） spectra are used in the studies of photoreaction kinetics. The results indicate that there is a relative stable stage arises after a very short initial stage. Based on FTIR studies, the monomer diffusion equation is deduced and necessary numerical simulations are carried out to analyse the monomer conversion which is an important point to improve phase separation structure of PDLC grating. Some simulation results have a good agreement with experimental data. In addition, the effects induced by monomer diffusion constant D and diffusion-polymerization-ratio rate R are discussed. Results show that monomer conversion can be improved by increasing value of D. Besides, a good equilibrium state （R = 1） is more beneficial to the diffusion of monomer which is important in the process of phase separation.

Electrically tunable holographic polymer templated blue phase liquid crystal grating

In this paper, we demonstrate an alternative approach to fabricating an electrically tunable holographic polymer tem- plated blue phase liquid crystal grating. This grating is obtained by preforming a polymer template comprised of periodic fringes, and then refilling it with a blue phase liquid crystal. Compared with conventional holographic polymer dispersed liquid crystal gratings, our grating can remarkably reduce its switching voltage from 200 V to 43 V while maintaining a sub-millisecond response time. The holographic polymer templated blue phase liquid crystal （HPTBPLC） grating is free from electrode patterning, thus leading to a lower cost and more flexible applications.

Effect of BaTiO₃Nanoparticle on Electro-Optical Properties of Polymer Dispersed Liquid Crystal Displays

Ferro nematic suspensions are the prominent materials to enhance the electro optical performance of liquid crystal displays. Electro optical properties of polymer dispersed liquid crystal (PDLC) display with the introduction of Barium Titanate nanoparticles have been investigated in this article and it is shown that there is a considerable enhancement in electro-optical response of the displays. The nanoparticles lower the switch-on electric field and thereby increase the optical transmission at certain voltages of the displays. The electro-optical characteristics of the PDLC cells were investigated with a He-Ne laser followed by MatLab calculations.

PREPARATION OF POLYMER DISPERSED LIQUID CRYSTALS USING PHOTOPOLYMERIZATION

2-Hydroxyethyl methacrylate (HEMA) and styrene copolymers are prepared by photopolymerization. The electrooptical behavior and microstructure of the polymer dispersed liquid crystal films are investigated by using He-Ne laser and scanning electron microscopy, respectively. With increasing E7 content in the copolymer, droplet size increased, threshold voltage decreased.

Effect of Polymer Network Morphology on the Performance of Polymer Dispersed Liquid Crystal (PDLC) Composite Films

The effects of the morphologies of liquid crystal (LC) droplets left in polymer network on the performance of polymer dispersed liquid crystal composite films were investigated.By adjusting the relative content range of the crosslinking and diluents,the morphologies of polymer network can be changed.Therefore,the properties of PDLC composite films with imparity polymer morphologies were obtained by experiments and the finite element simulation.Results of the experimental and finite element simulation showed that the electro-optical properties of PDLC composite films were inversely proportional to the domain size of the polymer network and the mechanical properties were proportional to the domain size of the polymer network.

Random lasing in dye-doped polymer dispersed liquid crystal film

A dye-doped polymer-dispersed liquid crystal film was designed and fabricated,and random lasing action was studied.A mixture of laser dye,nematic liquid crystal,chiral dopant,and PVA was used to prepare the dye-doped polymer-dispersed liquid crystal film by means of microcapsules.Scanning electron microscopy analysis showed that most liquid crystal droplets in the polymer matrix ranged from 30 μm to 40 μm,the size of the liquid crystal droplets was small.Under frequency doubled 532 nm Nd：YAG laser-pumped optical excitation,a plurality of discrete and sharp random laser radiation peaks could be measured in the range of 575–590 nm.The line-width of the lasing peak was 0.2 nm and the threshold of the random lasing was 9 m J.Under heating,the emission peaks of random lasing disappeared.By detecting the emission light spot energy distribution,the mechanism of radiation was found to be random lasing.The random lasing radiation mechanism was then analyzed and discussed.Experimental results indicated that the size of the liquid crystal droplets is the decisive factor that influences the lasing mechanism.The surface anchor role can be ignored when the size of the liquid crystal droplets in the polymer matrix is small,which is beneficial to form multiple scattering.The transmission path of photons is similar to that in a ring cavity,providing feedback to obtain random lasing output.

A Dual Effect of Au-Nanoparticles on Nucleic Acid Cholesteric Liquid-Crystalline Particles

Au-nanoparticles (size about 2 nm, but not 5 or 15 nm) are capable of effectively incorporating into quasinematic layers of particles of cholesteric liquid-crystalline dispersion formed by double-stranded nucleic acid molecules of various families (DNA and poly(I)xpoly(C)). This Au-size-dependent process is accompanied by a decrease in amplitudes of abnormal bands in the CD spectra specific to initial cholesteric liquid-crystalline dispersions and simultaneously by an appearance of plasmon resonance band in visible absorption spectrum. The study of properties of particles of cholesteric liquid-crystalline dispersion treated with Au-nanoparticles by means of various physico-chemical methods demonstrates that incorporation of Au-nanoparticles into quasinematic layers of these particles results in two effects: i) it facilitates reorganization of the spatial cholesteric structure of particles, and ii) it induces the formation of Au-clusters in the content of particles. It is not excluded that these effects represent a possible reason for genotoxicity of Au-nanopar- ticles.

Electrically tunable holographic waveguide display based on holographic polymer dispersed liquid crystal grating

In this Letter, we present an electrically tunable holographic waveguide display(HWD) based on two slanted holographic polymer dispersed liquid crystal(HPDLC) gratings. Experimental results show that a see-through effect is obtained in the HWD that both the display light from HWD and the ambient light can be clearly seen simultaneously. By applying an external electric field, the output intensity of the display light can be modulated,which is attributed to the field-induced rotation of the liquid crystal molecules in the two HPDLC gratings.We also show that this electrically tunable performance enables the HWD to adapt to different ambient light conditions. This study provides some ideas towards the development of HWD and its application in augmented reality.

Dynamic shaping of vectorial optical fields based on two-dimensional blazed holographic grating

We propose a vectorial optical field generation system based on two-dimensional blazed grating to high-efficiently generate structured optical fields with prescribed amplitude,phase,and polarization.In this system,an optimized blazed grating hologram is written on a spatial light modulator(SLM)and can diffract the majority of the incident light into the first-order diffractions of the x and y directions,which then serve as base vectors for synthesizing desired vector beams.Compared with the conventional cosine grating used in the previous work,the proposed two-dimensional,blazed grating has a much higher efficiency.Both computer simulation and optical experiment validate that a conversion efficiency up to 5 times that of the former work is achieved.Our method can facilitate applications of the optical field manipulation.

Passive patterned polymer dispersed liquid crystal transparent display

A patterned polymer dispersed liquid crystal transparent display using one-time UV exposure is demonstrated.The device is fabricated by exposing the cell with a uniform UV light through a mask with selective attenuation of the UV light.The voltage-transmittance response of the device is different for the corresponding regions.Thus,three different states of total scattering,patterned transparent,and total transparent can be realized by controlling the applied voltages.The proposed device used in shutter mode as smart windows and in projected display mode is demonstrated,which shows great potential for smart windows with customized patterns or logos and has potential application in the field of projected transparent displays.

聚合物分散液晶器件概述、发展趋势及应用研究进展

本文概述了聚合物分散液晶器件的基本结构、原理和制备方法,重点介绍了目前聚合物分散液晶器件(包括基于二色性染料的彩色器件以及基于柔性透明电极的柔性器件)的发展现状和趋势,总结了聚合物分散液晶在智能窗、防窥和传感器等方面的应用,最后对聚合物分散液晶器件色彩和柔性化方面的问题进行陈述,并对其研究方向进行了展望。

采用丙烯酸酯双单体的高空间频率透射式体全息H-PDLC光栅的研制

全息聚合物分散液晶(holographic-polymer dispersed liquid crystal, H-PDLC)体全息光栅因其化学状态稳定、制作简单、价格低廉等优势为全息光波导耦合器件提供了一个更优的思路。本文提出了采用复合型丙烯酸酯类高/低折射率匹配调制的H-PDLC透射式体光栅的研制。首先结合耦合波理论及分子扩散理论介绍了H-PDLC光栅的形成机理。然后,通过实验对不同官能度单体的光栅材料进行筛选,并研究其全息衍射特性。在此基础上,进一步采用提高引发剂含量的方式优化了高频体全息H-PDLC光栅性能。实验结果表明,该双单体的H-PDLC配方可实现在可见光波段透过率大于90%,在空间频率为973 lp/mm下,衍射效率达到90%,响应带宽为99 nm;在2 941 lp/mm下,衍射效率为75.4%,响应带宽为29 nm。该H-PDLC光栅作为波导显示系统的耦合器件有可观的应用前景。

聚氨酯丙烯酸酯的分子结构对聚合物分散液晶形貌和性能的影响

聚合物分散液晶(PDLC)是液晶畴均匀地分散在聚合物基体内形成的一种复合材料,因其制备简单、无需偏振片和取向层,在智能窗、柔性显示和可穿戴设备等领域具有广泛的应用前景。为了拓宽其在柔性显示器件上的应用,本文以聚氨酯丙烯酸酯(PUA)低聚物作为聚合物基体,采用紫外光聚合法制备PDLC器件,研究PUA的分子结构对聚合物分散液晶的形貌和性能的影响。实验结果表明,以丙烯酸酯基团进行封端的聚合物单体聚合速率快,形成了聚合物网孔状结构,且随着分子结构由脂肪族到芳香族的变化,聚合物网孔尺寸逐渐减小,使PDLC的驱动电压增高。利用聚氨酯中氨基甲酸酯键在分子链间形成的氢键增强与塑料基板的粘附性,获得了具有优异综合性能的PDLC器件。对比芳香族PUA,脂肪族PUA制备的PDLC样品具有较低的驱动电压(V_(th)=9.14 V,V_(sat)=35.50 V)、较高的对比度(CR=73.25)、较好的粘附性(20.11 N/cm^(2))以及在弯曲曲率半径为4 cm下弯曲前后光电性能变化幅度较小的特点,基本满足柔性PDLC在安全隐私保护以及弯曲表面的使用要求。

含氟单体材料对全息聚合物分散液晶Bragg光栅电光特性的影响

在全息聚合物分散液晶的预聚物体系中添加含氟的单丙烯酸酯单体,制备全息聚合物分散液晶Bragg光栅,通过AFM、He-Ne激光器观察分析,发现甲基丙烯酸十二氟庚酯(Actyflon-G04)的添加不仅改善聚合物基质的形貌,同时也影响光栅的电光特性。实验结果表明,光栅的衍射效率从78%上升到90%,驱动电压V90大幅降低。分析认为,Actyflon-G04的添加降低了聚合物界面的表面张力,影响液晶微滴的分子取向,从而实现了光栅电光特性的改善。

全息液晶/聚合物光栅的制备

将具有光敏特性的预聚物与向列相液晶按一定比例混合 ,以Ar+激光器为光源 ,使混合物在激光干涉光场的引发下发生光化学反应 ,从而导致液晶与预聚物发生相分离 ,形成全息液晶 /聚合物相位光栅。采用光学显微镜和He Ne激光器对所制样品进行测试 ,结果表明 ,当液晶含量在 30 %～ 45 %范围时 ,所制样品具有较好的栅结构 ,其衍射效率具有电场可调性。

基于聚合物分散液晶全息光栅的可调增益均衡器

从理论和实验两方面分析研究了聚合物分散液晶全息光栅在632.8nm光波的入射下的衍射谱特性和电压可调特性,实验结果与耦合波理论的计算结果具有很好的一致性,从实验上验证了用耦合波理论来描述聚合物分散液晶全息光栅的衍射特性是恰当的.并且提出了利用聚合物分散液晶全息光栅对掺饵光纤放大器增益谱进行平坦化的方法,利用聚合物分散液晶全息光栅的电压可调特性可实现动态增益均衡.运用该方法,可使掺饵光纤放大器在C波段1530～1560 nm内,温度在0℃～65℃范围内变化,掺饵光纤放大器自发辐射谱的不平坦度从3.3dB降到0.2dBp-p(峰-峰值).

聚合物分散液晶膜中液晶分子的电场取向效应

制备了液晶微滴在聚合物基体中呈独立分散且具有不同尺度的ＰＤＬＣ复合膜，利用偏光显微镜实时地观察了微滴内液晶织构在适度电场作用下的变化特性，获得了有关微滴内液晶分子的动态取向信息。实验发现，当施加的电压由饱合值降低时，不同尺度的微滴内液晶分子呈不同的电场取向效应，对直径大于十几微米的微滴，液晶分子易呈现较强的取向滞后效应，而直径在微米量级的液滴其液晶分子的电场取向滞后效应相对减少。微滴内液晶分子的这种取向滞后效应正是ＰＤＬＣ膜在宏观上呈现光透过率滞后现象的反映。从作用能的角度出发，讨论了影响微滴内液晶分子取向滞后效应的因素，如微滴与基体的界面作用、液晶微滴的形状、电容效应以及工作温度等。

应变液晶调光玻璃显示

介绍了聚合物分散液晶和应变液晶(SLC)的性质,SLC调光玻璃的结构特点,调光原理和光学特性以及制备方法。在SLC调光玻璃制备时,采用文字图案遮挡部分区域进行曝光,得到有文字图案的制品,遮光处形成透明状态,无遮光处处于散射状态。对制品施加剪切应力,散射区域变成半透明状态,文字图案消隐。依据此原理用SLC调光玻璃制作出一种特殊应力显示玻璃,可以开发成为节能的门窗等实用产品、在商场、公司以及酒店等场所装修上具有应用前景。

新型聚合物网络稳定液晶光栅的制备

将具有光敏特性的预聚物与向列相液晶按一定比例混合,注入液晶盒,以紫外灯为光源,通过光掩模法使混合物在紫外光的引发下产生相分离,形成聚合物网络稳定液晶光栅。采用光学显微镜和He Ne激光器进行测试,结果表明该光栅获得了周期性的栅结构,且衍射效率具有电场调谐性。

低阈值电压聚合物分散性液晶膜的电光特性

采用聚合物诱导相分离(PIPS)方法制备了PDLC膜,研究了不同单体材料、温度、光强等对PDLC膜电光特性的影响。发现Bi-EMA-2和EHMA混合单体(质量组分为1∶9)与液晶C70/02CN在折射率方面匹配较好,且在偏光显微镜下液晶微滴与聚合物单体的晶相边界清晰,易制备成对比度较高、阈值电压和饱和驱动电压较低的PDLC膜。温度和光强是控制和维持液晶与单体之间相分离速度平衡的重要工艺因素,直接影响到相分离过程中的液晶微滴形貌尺寸及其分布均一性,进而影响PDLC膜电光性能的优劣。通过工艺条件的优化,最终制备出了阈值电压为0.18 V/μm、饱和驱动电压为0.4 V/μm的PDLC膜。