Liquid Crystal Display Devices Research Articles

Stokes-Mueller calculus and θ-scan technology for investigating optical effects in liquid crystals doped with nanoparticles

The Stokes-Mueller calculus and θ-scan technology were used to investigate optical effects in liquid crystals doped with γ-Fe2O3 nanoparticles. The results showed that the dichroism decreased monotonously with increasing nanoparticle concentration, while the ellipticity decreased when the nanoparticle concentration increased from 0 to 0.06 wt%, but increased when the nanoparticle concentration increased from 0.06 wt% to 0.1 wt%. The apparent phase delay can be used to distinguish between different values of Nπ, revealing the intrinsic birefringence of the liquid crystal. The intrinsic birefringence decreases monotonically with increasing nanoparticle concentration. These results suggest that the optical properties of liquid crystals can be significantly modified by doping with nanoparticles. The findings of this study have important implications for the development of new liquid crystal display devices.

(Invited) Electrodeposition of In and Ga from Non-Aqueous Electrolytes

Indium and gallium are metals whose applications have increased during the last decades. Both metals are primarily used in the form of binary, tertiary or quaternary (semi)conductor compounds in integrated circuits, photovoltaics, liquid crystal display devices, lasers and light-emitting diodes.In the past, the electrodeposition of indium and gallium has been investigated from both aqueous and non-aqueous electrolytes. Due to the negative standard reduction potentials of the two metals (E°In(III)/In(0) = −0.34 V and E°Ga(III)/Ga(0) = −0.53 V), their electrodeposition from aqueous electrolytes is hampered. This is especially true for gallium. In this talk, the electrodeposition of indium and gallium was investigated from several organic solvents. The investigated electrolytes are 1,2-dimethoxyethane (DME), polyethylene glycol (PEG), dimethyl sulfoxide (DMSO), and acetonitrile, containing chloride, bistriflimide, or methanesulfonate-based indium or gallium precursors.The electrochemistry and the electrodeposition of indium and gallium was studied using various electrochemical methods in combination with quartz crystal microbalance (QCM) and rotating (ring) disk electrodes. DMSO-based electrolytes enabled the electrodeposition of indium at room temperature and above its melting point (159.6 °C), while DME electrolytes gave rise to gallium electrodeposits composed of small liquid gallium spheres (Fig 1). In all the investigated electrolytes, the formation of intermediate monovalent indium(I) or gallium(I) species during reduction and oxidation was demonstrated. These species are unstable and react away via disproportionation reactions. Yet, it was found that the extent of their formation and their stability depends on the nature of the electrolyte. In addition, the electrodeposition of indium antimonide (InSb) films and eutectic gallium indium (EGaIn) liquid metal lines and patterns will be discussed, as well as the electrochemical synthesis of spherical indium nanoparticles.

Temperature dependence of dynamic response of liquid crystal materials

Most properties of liquid crystal (LC) materials will change with the change of temperature, which makes the performance of liquid crystal display (LCD) and other devices change. However, at low temperature, the properties of LC will mutate with the decrease of temperature, which directly leads to the defects of LC devices. This paper makes use of the developed homemade temperature control device to realize the construction of high temperature to low temperature environment, using precision LCR meter (Agilent E4980A) and self-built optical path, combined with LC cell capacitance model and dual-cell model, the dynamic response properties of LC materials with temperature change law was explored. The results show that the decay time τ d of the LC with positive dielectric anisotropy increases from 12.04 ms to 159.7 ms, and the rotational viscosity coefficient γ 1 increases exponentially from 12.04 mPa·s to 1582.45 mPa·s. While τ d of the LC with negative dielectric anisotropy increases from 13.10 ms to 408.1 ms, γ 1 also increases exponentially from 162.73 mPa·s to 7903.69 mPa·s. The conclusions presented in this paper provide some guidance for the improvement of low temperature properties of LC.

High-performance narrow-band green-emitting phosphor enabled by substituting Na with Rb

Exploring green phosphors with satisfactory peak position (525–535 nm) and full width at half-maximum (FWHM) to replace the commercial narrow-band green β-SiAlON:Eu2+ phosphor (λem = 540 nm, FWHM = 54 nm) is crucial for realizing wide-gamut full-color liquid crystal display (LCD) devices. Here, taking the UCr4C4-type tetragonal phase RbNa3(Li3SiO4)4:3%Eu2+ (RN3(LSO)4:Eu2+) blue phosphor as starting model, we substitute Na+ with Rb+ to synthesize a series of Rb1+xNa2.97-x(Li3SiO4)4:3%Eu2+ (0.1 ≤ x ≤ 2.5) (R1+xN2.97-x(LSO)4:Eu2+) phosphors that exhibit tunable emission from blue to green. We demonstrate that Rb+-substitution triggers tetragonal-to-monoclinic phase transition, making Eu2+ ions enter two new, cuboid-like Rb and Na sites and resultant green emission. With optimized content of Rb+, Rb3Na(Li3SiO4)4:3%Eu2+ (R3N(LSO)4:Eu2+) green phosphor not only shows appropriate peak position (∼526 nm) and FWHM (∼43 nm) compared to β-SiAlON:Eu2+ phosphor, but also high internal quantum efficiency (IQE) of 90.2% and superior thermal stability (integrated emission intensity at 150 °C is 105.7% of room-temperature performance). Using the green R3N(LSO)4:Eu2+ phosphor, white light-emitting diode prototype shows a wide-color-gamut (111.2% National Television System Committee, NTSC). This work demonstrates that as-prepared green R3N(LSO)4:Eu2+ phosphor has a potential application in LCD backlight display, and may stimulate more researches on exploring high-performance narrow-band UCr4C4-type phosphors.

AYOLOv3-Tiny: An improved convolutional neural network architecture for real-time defect detection of PAD light guide plates

Light guide plates (LGPs) are the main component of the backlight unit of liquid crystal display (LCD) devices, and defective LGPs directly affect the display effect of LCDs. In view of the features of portable Android device (PAD) LGP images, such as complex texture background, low contrast, different defect sizes and various defect types and their optical properties, light-spot distribution, defect formation principle and imaging characteristics, this paper proposes an AYOLOv3-Tiny network for the defect detection of LGPs. First, by combining overlapping pooling and the spatial attention mechanism, the overlapping pooling spatial attention module (OSM) is constructed to replace the traditional convolution operation of the YOLOv3-Tiny backbone network. Overlapping pooling can improve the accuracy and prevent overfitting, and the spatial attention mechanism can help the network better extract defect features. Second, a dilated convolution module (DCM) is constructed in the detection branch. The module can expand the receptive field of the convolution kernel and improve the detection ability of large defects by integrating the dilated convolution into the residual network structure. Third, a large number of experiments based on the self-built dataset PAD LGP SDD are carried out. The experimental results show that the mean average precision (mAP) and F1-score of the LGP defect detection system can reach 99.50% and 99.61% respectively, and the detection speed can reach 144 fps. Finally, by testing on the PAD LGP images with defects, it is verified that the proposed network meets the application requirements of high precision and real-time online detection of PAD LGP images.

Rodlike 4,6-diamino-1,3,5-triazine derivatives, effect of the core length on mesophase behavior and their application as LE-LCD device

Three series of diaminotriazine derivatives with different core length have been synthesized, and the influence of the structural variation as well as the temperature on their mesophase behaviour were systematically investigated. With focus on the formation of CubI/Im3¯m phase, multiple 2D/3D phases were discovered. Confirmed by polarized optical microscope, small/wide angle X-ray scattering, grazing incident small-angle X-ray scattering as well as molecular dynamics simulation, the results indicate that molecular curvature is critical to self-assembly structures. Moreover, the prerequisite for the formation of the CubI/Im3¯m phase is intermediate molecular curvature on the surface of the micelle to allow the intercalation of the alkyl chains. Finally, the potentials for such compounds as light-emitting liquid crystal display (LE-LCD) device has been initially demonstrated.

A Light‐Emitting Liquid Crystal Display Device without Polarizers and Alignment Layers

AbstractLight‐emitting displays become the future direction of display technology for the radical requirement of reducing energy consumption. Here, an approach of fabricating a luminescent liquid crystal (LE‐LC) display device without polarizers and alignment layers is reported, achieved by using an aggregation‐induced emission (AIE)‐active LE‐LC mixture. Through studying the relationship between emission of the LE‐LC at several orientation modes and the concentration of the AIE‐featured fluorescent dye, the difference of fluorescence at aggregation state is revealed. When the concentration of the fluorescent dye is high enough, the emission of the planar‐aligned LE‐LCs is ≈4 times of the vertical‐aligned LE‐LCs. An electronically controlled LE‐LC cell is thus constructed, in which the homeotropic alignment of liquid crystals is induced by doping of CuInS2 nanoparticles. Therefore, this simple LE‐LC display avoids the use of polarizers and alignment layers, raising the exciting possibility of development of high efficiency and low energy‐consumption LE‐LC devices.

Mesomeric Effects of Azobenzene Bearing Natural Product-Based Molecules for Liquid Crystal Materials: An Overview.

Latest progress in the liquid crystal (LC) field related to azo molecules incorporated into natural product- based moieties for the improvement of LC texture and mesomeric phases has received great interest among researchers. A LC containing natural product-based moieties i.e. menthol, kojic acid, cholesterol and chalcone with stable azo and azobenzene scaffolds with specific optical tunability, has been widely used in photo-active materials such as Liquid Crystal Display (LCD), LC films, smart windows and other devices. This review discusses the influence of azobenzene, a renowned photo-responsive and stable LC scaffold, in mesogenic phases due to photo-isomerization and optical switching. The incorporation of mesomeric phases of natural product moieties to azo molecules has improved the properties of LC, i.e, from the nematic phase to the smectic phase with proper magnetic field alignment. Natural product-based LC can be useful in numerous applications, especially practical electronic or optic devices such as optical image storage, display devices, solar cells, optical switching.

P‐148: Investigation of photoluminescence and birefringence of nanoparticles dispersed nematic liquid crystal and its application towards liquid crystal display and optoelectronic devices

In the present investigation nanoparticles (NPs) have been dispersed into the pure nematic liquid crystal (NLC). NPs have been dispersed into the NLC with two different concentrations. Polarizing optical microscope (POD imnages have been recorded for pure NLC and NP dispersed system in the planar aligned liquid crystal cell. The dispersion of NPs in NLC increases the photoluminescence intensity which is an important finding of this study. Birefringence has also been measured here with the help of transmittance technique and it has been observed that the birefringence got increased after the dispersion of NPs into pure NLC. This is the key finding of the present reported work. Relative electric permittivity has also been measured here and found to be increased for the dispersed system as compared to the pure NLC. It is suggested that the output of the present work may be very useful in liquid crystal display and photonic applications.

P‐11.15: The Influence of chiral dopant on the Rewriting Speed of Optically Driving Liquid Crystal Display

For a liquid crystal display device, like optically driving liquid crystal display (ODLCD), the response time plays a crucial role. In this paper, a new method is proposed to increase the rewriting speed of ODLCD. With chiral dopant mixing with the liquid crystal 5CB, the rewriting time can be increased by 1.5 times.

Surface Processing of Polyethylene Terephthalate for Orientation of Nematics in Display Devices

Thermoplastic polymers have found widespread applicability in electronic industry owing to their facile processing and relatively low costs. Transparent polymer foils, like polyethylene terephthalate (PET), can be utilized in manufacturing components for liquid crystal display (LCD) devices. This work is focused on surface processing of PET through different procedures. The induced surface modifications of polymer samples were analyzed by optical microscopy. Contact angles of nematic drops on PET film are measured to evaluate how the method of surface modification reveals that the surface texturing affects the interactions of polymer with the liquid crystal. The influence of created surface anisotropy on the work of adhesion at polymer/liquid crystal interface is analyzed. Preliminary assessment of nematic orientation on the surface of modified PET foils is performed using polarized light. The results were discussed in regard with the used methodology to adapt the surface of the PET films to achieve optimal orientation of nematic molecules. The obtained data will open new perspectives on processing polymer foils as alignment layers used in LCD devices.

Nano P(VDF-TrFE) doped polyimide alignment layers for twisted nematic liquid crystal devices

ABSTRACTThe rapid development of consumer electronics and portable devices imposes a great demand for energy efficient information display systems. Among the information display devices, liquid crystal display (LCD) devices stands in the front. The fabrication of energy-efficient LCD systems demands new material and techniques. In this work, the conventional polyimide alignment layer of twisted nematic liquid crystal device (TNLCD) was replaced with ferroelectric polymer nanoparticle doped alignment layer. Morphology of the alignment layer was analysed using field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). The ferroelectric nature of the polymer alignment layer was studied using dynamic contact electrostatic force microscopy (DC-EFM). TNLCD cells are fabricated with this modified alignment layer and the switching characteristics are compared with the conventional TNLCD devices. The TNLCD with modified alignment layer has shown a reduction of 50% in threshold (Vthr) and 47% reduction in saturation voltage (Vsat).

Recycling of waste glass generated from end-of-life LCD devices: A feasibility study using simulated waste glass

The liquid crystal display (LCD) industry has undergone drastic growth over the past decade. Considering that the lifetime of an LCD device is approximately ten years, a huge end LCD waste glass (ELWG) is being produced from end-of-life LCD devices. The recycling of ELWG derived from LCD device produced before 2011 is limited by the presence of toxic components such as As, Sb and Ba. In this work, the potential of recycling ELWG was examined to be used in the glass wool industry. 17 glass batches using four different simulated ELWGs (mixtures corresponding to LCD glasses produced in 2006, 2008, 2009, and 2010) were prepared and melted. ELWG was introduced up to 20% of the total glass. Two fixed viscosity points (Tm, Tw) corresponding to 102 and 103 dPas, and the liquidus temperature (TL) were determined in the melt state, and leaching tests of the glass powder in an acidic solution based on the toxicity characteristic leaching procedure (TCLP) were also carried out. As the ELWG content was increased, the Tm, Tw, and TL values did not show a linear relationship with the ELWG content, but some fluctuation in the values was observed. The Tm value showed a larger deviation of 28–36 °C from that of the original glass than the Tw (6–14 °C) and TL (2–16 °C) values. As and Sb were not detected in the leaching tests, and the Ba concentration (1.232–2.279 mg/L) was much lower than the TCLP regulatory level (100 mg/L). The observed TW-TL values suggested that the replacement of 20% or more of the total glass by ELWG is possible. Additionally, the economic and environmental effects of the recycling process were discussed.

Photo‐aligning of polyimide layers for liquid crystals

A series of soluble and highly transparent semi‐alicyclic polyimides (PIs) with designed flexible linkages have been synthesized derived from an alicyclic aromatic dianhydride (1,2,3,4‐cyclobutanetetracarboxylic dianhydride, CBDA) and various aromatic ether‐bridged diamines. The semi‐alicyclic PIs were evaluated as the photo‐alignment layers of liquid crystal (LC) molecules in liquid crystal display (LCD). Experimental results indicate that the photo‐alignment characteristics of LC molecules induced by the photo‐aligned PI layers and the electro‐optical (EO) properties of the LC cell devices are closely related with PI backbone structures. The retardation of the photo‐aligned PI layers is correlated with the ultraviolet (UV) absorption intensity of PI at 220 to approximately 330 nm. The higher UV absorption intensity PI has, the higher retardation and lower pre‐tilt angle the photo‐aligned PI layer exhibits. The defect‐free and photo‐aligned PI layer could result into the uniform LC texture, which is highly desired for in‐plane switching (IPS) mode LCD devices. In comparison, PI layer containing trifluoromethyl moiety shows poor photo‐aligning performance because of the strong electronic withdrawing effect of the fluorinated linkage.

Power-Constrained Image Enhancement Using Multiband Processing for TFT LCD Devices With an Edge LED Backlight Unit

This paper presents a subband-decomposed image-enhancement algorithm that can preserve the luminance and contrast levels in power-controllable thin-film-transistor liquid-crystal display devices. The proposed algorithm consists of three steps. First, an input image is decomposed to multiscale subbands via subband decomposition. Second, luminance compensation and contrast preservation are achieved simultaneously by adjusting the gain of each subband properly. Third, additional power consumption caused by excessive boosting, while coping with the local dimming through specific clipping, is prevented. The experimental results show that the proposed algorithm provides more natural details and contrast, while preserving more similarities with the original, than the existing methods. Even in terms of the peak signal-to-noise-ratio and the structural similarity index, the proposed algorithm has 27.8% and 3.8% higher values compared to a state-of-the-art method. The real-time operation of the proposed algorithm was verified through intensive optimization and the Compute Unified Device Architecture implementation. In addition, the power-reduction effect of the proposed algorithm on commercial monitors was investigated experimentally.

SYNTHESIS OF (E,E)-AZOAZOMETHINES BASED ON 4-AMINOAZOBENZENE

Liquid crystal display devices are widely used in industries such as measuring instrumentation, consumer and industrial electronics, medical equipment and others. The production of these devices is a promising and growing branch of industry in Belarus. The analysis of the liquid crystal device market suggests that the demand for film polarizers of all types (transmissive, reflective and permeable-reflective) will increase due to the constant growth of liquid crystal device manufacture and their scope expanding. Currently, manufacturers of liquid crystal devices in Belarus buy polarizers abroad, and the price is determined by the manufacturers. Obviously, the researches aimed at creating domestic film polarizers of various functional purposes and for the development of technologies for their manufacture, are relevant. 4-aminoazobenzene (aniline yellow colorant) is used in the production of more complex intermediates, dyestuffs, chemical additives to polymers, pharmaceuticals, pesticides, etc. 4-aminoazobenzene is an accessible parent compound for the synthesis of promising compounds for the development of optical materials. By reaction of 4-aminoazobenzene series with vanillin aldehydes in a medium of boiling absolute methanol in the presence of catalytic amounts of glacial acetic acid, (E,E)-azoazomethynes with 75–88 % yields were synthesized.

Optical rewritable liquid crystal displays without a front polarizer.

A front polarizer-free optically rewritable (ORW) liquid crystal display (LCD) has been made via a hybrid alignment configuration with dye-doped LCs. The hybrid structure consists of one optically active planar and one optically passive homeotropic alignment layer. The rewritability of the device is achieved by photo-reorienting the azo dye molecules in the active planar alignment layer. The dye is doped in LCs to function as a polarizer by following the LCs' direction via a guest-host effect so that the front polarizer can be eliminated. This makes the device more compact and easier to operate for image erasing and rewriting. The image rewriting time only requires ∼9.0 s, which is determined by the exposure energy and LC parameters. The hybrid-mode dye-doped ORW LCD devices could find applications in E-paper, transparent display, and various photonics devices.

Tailoring arbitrary hybrid Poincaré beams through a single hologram

Hybrid Poincaré beams (HPBs) are a kind of structure field with anisotropic polarizations. Here, we demonstrate an approach to tailor HPBs with arbitrary states, through encoding a single hologram on a liquid-crystal display device along with a stable optical system. The state of the obtained HPB is determined only by the encoded holograms with special design, which means it is not necessary to adjust any optical elements or hardware when generating various HPB states. Moreover, perfect HPBs can also be generated through the proposed scheme. In the experiment, the obtained HPBs are analyzed through a polarizer and a special parameter S3/S0, showing good agreement with prediction. This work opens an insight in encoding single holograms for tailoring arbitrary HPBs and inspires various applications.

Increasing the rewriting speed of ORW e-paper by electric field

ABSTRACTFor a liquid crystal display device, like optically rewritable (ORW) e-paper, the response time plays a crucial role. In this article, a new method is proposed to increase the rewriting speed of ORW e-paper. Effective rotational viscosity is very important for the dynamic result, the rewriting time can be increased by four times by applying electric field across the liquid crystal cell, i.e. decrease the effective rotational viscosity .

Partially biobased processable polyimides based on aromatic diamine derived from cardanol

A partially biobased aromatic diamine – namely, 1,1-bis(4-aminophenyl)-3-pentadecylcyclohexane (BAC15) – was synthesized starting from cardanol. A series of polyimides were synthesized by one-step high-temperature solution polycondensation of BAC15 with aromatic dianhydrides. Copolyimides were also synthesized by polycondensation of various compositions of BAC15 and 4,4′-oxydianiline with 3,3′,4,4′-biphenyl tetracarboxylic dianhydride. The inherent viscosities and number-average molecular weights of (co)polyimides were in the range of 0·33–1·4 dl/g and 14 700–31 900 g/mol, respectively, indicating formation of reasonably high-molecular-weight polymers. Polyimides were soluble in common organic solvents such as chloroform, dichloromethane and tetrahydrofuran and could be cast into transparent, flexible and tough films from their solutions in chloroform. (Co)Polyimides exhibited glass transition temperatures (T g) in the range of 161–254°C. The lowering of T g could be attributed to the presence of flexible pentadecyl chains, which act as ‘packing-disruptive’ groups. The temperature at 10% weight loss (T 10) of (co)polyimides was in the range of 490–515°C, demonstrating their good thermal stability. The virtue of solubility and the large gap between T g and T 10 offers (co)polyimides opportunities of both solution and melt processability. Copolyimides containing pendent pentadecyl chains exhibited pretilt angles in the range of 2·51–2·75°, indicating their potential application as an alignment layer in liquid crystal display (LCD) devices.