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.

NOVEL POLYMER WIDE VIEWING ANGLE COMPENSATION FILMS FOR LIQUID CRYSTAL DISPLAYS(LCDS)

We report on generating uniaxial negative birefringent compensation films, made of specifically designedpolyimides. These polymers were synthesized via a polycondensation of dianhydride [such as 2, 2' -bis(3, 4-dicarboxyphenyl)hexafluoropropane dianhydride] and 2, 2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl. The uniaxial negative birefringent (n_x =n_y > n_z) polyimide substrates are achieved using a solution-casting method in conventional solvents, which exhibit thedesirable optical phase retardation [(n_x - n_z)×d] values from 50 to 400 nm varying with the film thickness. In thesepolyimide films, the long chain rigid molecules adopt intrinsic planar orientaion. In detail, the majority of phenylene-imiderings and phenylenes preferentially adopt nearly planar conformations parallel to the film substrae. In addition, these filmsalso possess high transparency (or transmittance) and little color shift. The unique color dispersion curve indicates that thistype of materials is very suitable for the applications in LCDs due to an excellent mimic for the retardation color dispersioncurve with respect to LC molecules. Significantly low in-plane retardation (< 1 nm) allows this new technology based film toachieve sufficiently high contrast ratio while highly negative retardation dramatically suppresses the gray scale inversion toimprove the viewing angle performance in a variety of new mode LCDs.

Fabrication and structure of Langmuir-Blodgett films of ferroelectric liquid crystal

The molecular aggregation, orientation, and structure in Langmuir-Blodgett films of ferroelectric liquid crystal were studied by ultraviolet and Fourier transform infrared spectra. The results show that medium strong (H-aggregates) in the Langmuir-Blodgett films of ferroelectric liquid crystal are formed by chromophores where the alkyl chains are nearly perpendicular to the film surface. Compared with the cast films, the CO stretching bands, due to the rotational isomerism around the O—C axis of the chiral part, can be identified clearly in Langmuir-Blodgett films.

Near-field lithography on the azobenzene polymer liquid crystal films

In this article, we reported near-field research on azobenzene polymer liquid crystal films using scanning near-field optical microscopy （SNOM）. Optical writing and subsequently topographic reading of the patterns with subwavelength resolution were carried out in our experiments. Nanometer scale dots and lines were successfully fabricated on the films and the smallest dot diameter is about 120 nm. The width of the line fabricated is about 250 nm. This method is also a choice for nanolithography. The mechanism of the surface deformation on the polymer films was briefly analyzed from the viewpoint of gradient force in the optical near field. The intensity distribution of the electric field near the tip aperture was numerically simulated using finite-difference time-domain （FDTD） method and the numerical simulation results were consistent with the experimental results.

Helix unwinding in ferroelectric liquid crystals induced by tilted electric field

Helix unwinding in ferroelectric liquid crystals induced by an electric field is theoretically studied on the basis of the continuum theory. By applying a weak electric field tilted to the smectic layers, the contribution of the dielectric interaction energy density to the total free energy density is increased. Approximation methods are used to calculate the free energy for different tilt angles between the electric field and the smectic layers. The obtained results suggest selecting the optimal number of pitches in the film that matches to the minimum of the free energy.

Optical Properties of Aligned Nematic Liquid Crystals in Electric Field

In this study, the optical transmittance of aligned nematic liquid crystals (ANLCs) was investigated in terms of temperature variations through electrooptic effects under DC electric field. The optical transmittances of the planar and homeotropically aligned liquid crystal cells, which were prepared by conventional rubbing and photolithographic technique on the polyimide thin films for molecular alignment, were measured in their phase transition region. The results of measurement for both orientations, the distribution curve of the optical transmittance exhibits displacement toward to low level at the beginning and then to high level by the temperature variations, while the electric field increases. It was also observed that the domain structure of the materials were affected considerably by the applied electric field and phase transition region of the aligned structures had broader range than by the pure crystalline structure and its phase transition temperature was changed by the molecular anisotropy. Finally, in photolithographic method strong bonds between the molecules and the orienting surface were observed in high contrast to rubbing method.

热致液晶高分子膜的表面处理及化学镀铜

论文采用氢氧化钠(NaOH)溶液对Vecstar型热致液晶高分子(TLCP)膜表面进行刻蚀粗化,然后通过3-氨丙基三乙氧基硅烷(KH550)在膜表面引入氨基,利用氨基络合银离子使膜表面活化,再进行无钯化学镀铜,提升了TLCP膜与金属铜之间的黏附力。借助扫描电子显微镜(SEM)、接触角测量仪、X射线衍射仪(XRD)和剥离测试等对经表面处理及化学镀铜后的TLCP膜进行表征,探讨了NaOH溶液浓度、表面粗化温度和时间、活化溶液组成等对TLCP表面化学镀铜的影响。结果表明,经表面处理后TLCP膜表面产生均匀的孔洞,接触角下降至29.30°,亲水性大幅提高;所镀铜层呈光亮的粉色,带有金属光泽,致密平滑,纯度高,镀层厚度可达2.78μm,与TLCP膜间的附着力等级达到了5B。

聚乙二醇/纤维素纳米晶体复合液晶薄膜微观结构及湿度响应行为

【目的】探索聚乙二醇(PEG)对纤维素纳米晶体(CNC)液晶薄膜湿度响应的影响,阐明其响应机制,旨在为开发低成本、可重复使用和高灵敏度的PEG/CNC复合薄膜湿度传感器提供理论基础。【方法】将CNC与PEG共组装,制备了一种具有湿度响应性能的虹彩色手性向列相光子液晶薄膜,系统考察了PEG质量分数对液晶薄膜的微观结构、显色、力学性能及湿度响应的影响,在此基础上,研究了PEG/CNC复合液晶薄膜在不同湿度条件下的响应循环性能。【结果】对于纯CNC体系,CNC质量分数由3%增加到7%,CNC液晶薄膜的螺距减小,最大反射光波长由596.5 nm蓝移至511.0 nm;对于添加PEG的CNC体系,随着PEG质量分数的增加,PEG/CNC复合液晶薄膜的螺距由394.0 nm减小到244.0 nm,最大反射光波长由613.5 nm蓝移至350.5 nm,韧性先提升后下降,PEG质量分数为5%时为最佳,断裂能为31.9 J·m^(-2),较纯CNC薄膜提升了138%;液晶薄膜经过5次吸湿-解湿,表现出良好的湿度响应重复性,平衡波长的变化率小于0.6%。【结论】制备了一种对湿度具有敏感响应的虹彩色光子PEG/CNC复合液晶薄膜,PEG可以调控复合薄膜螺距,起到调节结构色的作用。

液晶高分子薄膜的热处理及结晶行为

为探究液晶高分子(LCP)薄膜在热处理过程中结晶行为,利用差示扫描量热(DSC)仪对LCP薄膜进行热处理,考察了在不同热处理条件下LCP薄膜熔点和熔融焓的变化,并分析其结晶转变。非等温结晶实验结果表明LCP薄膜熔融后的再结晶快过程难以避免,且形成新晶体的熔融特征与降温速率无关。等温结晶实验结果表明慢过程无法完全抑制快过程,且LCP薄膜经慢过程形成新晶体的温度上限为270℃。不同条件的等温热处理实验结果表明,低温段热处理有利于提高熔融焓,熔程上限以下的高温段热处理则更有利于提高熔点,在240℃等温热处理60 min得到最大熔融焓为3.87 J/g,在290℃等温热处理60 min得到最高熔点为306.8℃。通过分峰定性LCP薄膜在不同热处理温度下的结晶趋势,分析得到慢过程中形成新晶体、原晶体生长(包括熔融-再结晶的晶体)与冷却快过程形成新晶体的最佳温度分别为LCP薄膜的结晶温度、熔程下限温度与熔程上限温度。最终,结合LCP薄膜热处理前后的晶体结构模型,总结LCP薄膜在热处理中的结晶转变,为规模化制备高性能LCP薄膜提供参考。

密封沉积处理对纤维素纳米晶体薄膜光学特性的调控

纤维素纳米晶体(Cellulose nanocrystal,CNC)在特定浓度下可自组装排列,赋予体系独特的光学性能。为阐明CNC薄膜形成过程中CNC自组装行为机制,本文通过分析CNC薄膜在宏观颜色、紫外可见光谱、偏振光学、微观形貌以及晶体结构等方面的变化,探究了密封沉积时间和CNC浓度对自然蒸发干燥薄膜内部胆甾相液晶形成与排列的影响。结果表明,当密封沉积时间延长至48 h后,CNC薄膜的结构色显色范围、胆甾相结构的长程有序性均得到明显提升。随着浓度的升高,CNC颗粒间距减小,相邻颗粒间扭转角增大,螺距被压缩,从480 nm减小至344 nm。此外,密封沉积处理对高浓度CNC悬浮液形成长程有序性胆甾相结构具有明显优势。本研究结果表明,延长密封沉积时间和提高CNC浓度可以提高薄膜中长程有序性的提高,并促进胆甾相结构域的形成。这进一步完善了CNC基智能包装材料制备的科学基础,对于新型可视化食品包装和检测材料的开发具有积极作用。

用于防伪商标的液晶柔性显示薄膜

本文设计了一款机械性能优异和具有独特防伪功能的液晶柔性显示薄膜。首先,基于光控取向技术设计了一款具备双通道显示功能的液晶显示器件,通过光场调控实现两个通道的独立显示。其次,以液晶盒厚度作为对照组确定了最佳厚度,使两个独立图案形成主副显示效果,从而隐藏防伪信息。最后,通过在液晶-聚合物复合材料中掺杂银纳米线(AgNWs)改善了液晶显示薄膜的机械拉伸性能。实验结果表明,在液晶柔性显示薄膜厚度为60μm时,其呈现令人满意的图案显示效果。同时,与未掺杂AgNWs的液晶显示薄膜相比,掺杂了AgNWs的液晶柔性薄膜的模量参数提高了30%以上,具备更大的应力承受能力和应变范围。本研究对于制备信息丰富且稳定性强的液晶防伪商标具有积极意义。

冷气流量比对三维涡轮导叶全气膜冷却效率的影响

为了研究不同主流湍流度下冷气质量流量比对三维涡轮导叶全气膜冷却特性的影响,使用热色液晶测量了在主流湍流度为1%和15%,流量比为5.5%、8.4%和12.5%下三维涡轮导叶的全气膜冷却效率分布。结果表明:在不同的叶片区域和主流湍流度下,流量比对气膜冷却特性的影响规律也有所不同;在低主流湍流度下,冷却效率整体上随着流量比的增大而升高,但是在叶片的叶尖和吸力面中截面区域冷却效率在大流量比下降低,且叶片吸力面中弦区域的冷气呈波纹状分布;高主流湍流度使冷气射流与主流之间的掺混更加剧烈,可以抑制吸力面的冷气脱离壁面且使其分布更加均匀,冷却效率随流量比增大而升高。

Al_xGa_(1-x)As/GaAs Solar Cell Grown by Multi-substrate Liquid Phase Epitaxy

A novel horizontal push-pull multi-substrate epitaxy boat with three separate cells is introduced in this article, with which multi-substrate LPE processing is feasible in horizontal LPE furnace. The processes of LPE AlxGa1-x)As/ GaAs solar cells are studied and the efficiency of the solar cells achieved 19.8% （AMO, 25℃, 120 mW/cm2）.

Electro–optic response in thin smectic C* film with chevron structures

The effects in electrostatic models of chevron surface-stabilized ferroelectric liquid crystals are investigated through numerical modeling. To study smectic C＊ director distribution within the cell, we consider two nonlinear approaches： the chevron interface does not interplay with the electric field; the electric field interplays with the chevron interface. The obtained results of the director field distribution are compared with the earlier linearized studies. We find that whether or not the electric field interplays with the chevron interface, the electro-optic response requires a generalized approach for its description. The threshold electric field, which is necessary for switching between two stable director states in the chevron cell is evaluated. This study suggests that, in many cases of practical interest, electro-optic response to the electric field and the threshold electric field can be precisely estimated. We argue that, beside being numerically efficient, our approach provides a convenient and a novel standpoint for looking at the electro-optic response problem.

基于Swin Transformer轻量化的TFT-LCD面板缺陷分类算法

在TFT-LCD面板缺陷检测中,检测对象背景复杂、缺陷细微且种类繁多,而工业生产实时性要求高,传统的缺陷分类算法往往难以兼顾精度和速度要求,无法适用于实际生产应用。为均衡TFT-LCD面板缺陷分类的准确率和速率,提出一种基于Swin Transformer的轻量化深度学习图像分类模型。首先对模型每层输入的特征图进行Token融合以减少模型计算量,从而提高模型的轻量化水平。其次引入深度可分离卷积模块以帮助模型增加卷积归纳偏置,从而缓解模型对海量数据的依赖问题。最后使用知识蒸馏方法来克服模型轻量化导致的检测精度下降问题。在自制TFT-LCD面板缺陷分类数据集上的实验表明,本文提出的改进模型相比基线模型,FLOPs计算量降低了2.6 G,速度指标提升了17%,而Top-1 Acc精度仅损失1.3%,且与其他图像分类主流模型相比,在自制数据集和公开数据集上都具有更均衡的精度和速度。

多色柔性自支撑胆甾相液晶薄膜反射器件

一维手性软光子晶体胆甾相液晶(CLC)在防伪标签、纳米激光器和传感等领域具有广泛的应用。本文采用多步图案化紫外固化方法并结合清洗-重填工艺,实现了多色的柔性自支撑CLC薄膜反射器件。采用标签打印机打印PET图案作为掩膜版,对可聚合的CLC材料进行紫外固化,得到图案化的柔性自支撑CLC薄膜反射器件。在此基础上,将非固化区域的液晶材料洗去并重新填充不同手性剂含量的CLC,再次图案化紫外曝光,即可实现多色的柔性自支撑CLC薄膜反射器件。研究了不同入射角、弯曲曲率半径和温度对反射器件光学性能的影响。实验结果表明,采用上述方法制备的多色可自支撑反射器件具有良好的柔性,不同曲率半径下的布拉格反射中心波长基本不变。随着温度升高,布拉格反射中心波长红移,且具有良好的线性度。多色的可自支撑柔性薄膜反射器件可拓展CLC在显示、传感、激光防护和微纳光学等领域的进一步应用。

联苯类液晶改性纤维素膜的制备及其抗紫外性能

以1,6-二溴己烷、氰基联苯酚和N-甲基咪唑为主要原料,合成含有咪唑基团的联苯类液晶(CbP)。以离子液体1-烯丙基-3-甲基咪唑氯盐(AMIM·Cl)为溶剂,将木浆纤维素(WPC)与CbP共混得到铸膜液,再通过浸渍沉淀相转化技术将铸膜液制成纤维素液晶膜(WPC/CbP)。采用哈克流变仪对溶液性能进行表征,用傅里叶红外光谱(FT-IR)、X-射线光电子能谱(XPS)、差示扫描量热(DSC)等对膜结构和性能进行表征。结果表明,CbP的引入改变了纤维素分子内及分子间的氢键作用,提高了纤维素膜的热稳定性。当CbP在铸膜液中的质量分数为3%时,溶液黏度最低。与纯纤维素膜相比,此WPC/CbP膜的拉伸强度提高了27.56%,紫外光透光率降低了35%左右。

刺激响应性胆甾型液晶软光子彩膜

为实现软光子晶体图案的多重信息加密或存储,本文基于硫醇-丙烯酸酯Michael加成和光聚合反应设计并制备了一种刺激响应性胆甾型液晶(cholesteric liquid crystal,CLC)软光子彩膜。首先,通过改变反应混合物中手性剂的比重调节初始彩膜结构色;其次,用小分子液晶稀释液晶前聚体;最后,通过紫外光固化对单层软光子彩膜进行交联密度的时间编程,同时借助掩膜曝光技术对其纳米结构进行空间编程。实验结果表明,虽然在超600 min的反应过程中软光子彩膜的布拉格反射中心波长仅移动了19 nm,但是通过时间-空间双重编程局部修改其变色响应,可使带有隐形图案的软光子薄膜在应力作用下逐渐呈现从红到绿的多彩外观,反射波长覆盖范围超过100 nm。这种刺激响应性软光子彩膜在光子晶体图案的动态显示、防伪、信息存储等领域具有重要的应用价值。

液相外延法制备的掺杂石榴石单晶薄膜

以高纯氧化物为原材料,采用液相外延法(LPE)制备直径3英寸、厚度20μm以上的掺杂钇铁石榴石(YIG)单晶薄膜,通过离子掺杂对薄膜的饱和磁化强度进行调控,范围为800~1750 G。X射线衍射分析表明薄膜仅有单一衍射峰,且半高宽值约为0.007°。磁性能测试结果表明,制备的薄膜饱和磁化强度可宽幅调控,且呈现明显的平面磁各向异性。同时对薄膜的截面及表面形貌进行观测,发现薄膜与衬底间界面清晰,薄膜表面粗糙度小于1nm,离子掺杂均匀,为后续的器件应用打下良好的基础。

Investigations of the mechanism of liquid-crystal alignment onrubbed polyimide films

Liquid crystals (LCs) can be easily oriented by surfaces on a macroscopic scale. Thisphenomenon, known as alignment or anchoring, plays a dominant role in the fabrication ofLC devices. Studying the alignment technique of LCs is of great importance from bothpractical and theoretical points of view. Recently, rubbed polyimide-coated glass substrates have been widely used in LC align-ment. A general belief about the mechanism by which such a polymer alignment methodworks is that alignment acts through the interaction between LC molecules and orientedpolymer chains. This assumption was demonstrated by Barmentlo et al. through surfacesecond-harmonic-generation and optical phase retardation measurements. However, theseoptical techniques can only provide the macroscopic and average information because