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Spontaneous formation of chiral domains such as a helical filament and a bent-broom texture was observed from the mixture of a rod-like liquid crystal octylcyano-biphenyl (8CB) and a tri boomerang-shaped 2,4,6-triphenoxy-1,3,5-triazine (triphenoxy) molecule. Although the constituent molecules were achiral, their mixture showed the chiral domains with the equal fraction of the opposite handedness. No tilt of 8CB molecules in the smectic layer was observed, implying the chirality is not due to the polar packing and tilt of the molecules. In addition, the splay and bend elastic constant of 8CB was decreased after doping triphenoxy. A structural conformation of triphenoxy and an orientational coupling between 8CB and triphenoxy are considered to be related to the chiral domain formation. [ABSTRACT FROM AUTHOR]

When an electric field is applied to a nematic liquid crystal cell with splay alignment layers, which is realized by mechanical parallel rubbing, the system exhibits abnormal reverse tilt domains. Even though the system has pretilt angle due to symmetry breaking by rubbing, existence of singular point in a cell by splay geometry and shift of that by locally asymmetric pretilt angle configurations result in the abnormal reverse tilt domains. On the basis of Oseen-Frank theory, dependence of singular point upon the abnormal reverse tilt domains is theoretically investigated for a splay alignment liquid crystal cell. By using the Dickman’s Q-tensor method [SID Int. Symp. Digest Tech. Papers 24, 638 (1993)], liquid crystal director field is calculated for the splay-aligned liquid crystal cell that an electric field is applied to. We presume a model to explain the abnormal reverse tilt domains, and derive the conditions required for the generation and elimination of these domains. [ABSTRACT FROM AUTHOR]

We propose an achromatic optical compensation method using uniaxial films to eliminate the off-axis light leakage in a homogeneously-aligned liquid crystal cell. In this technique, four uniaxial films with complementary dispersion characteristics are used to compensate for one another, resulting in achromatic effective phase retardation for off-axis angles. The retardation values are optimized with the aid of the Poincaré sphere and through numerical research. The contrast ratio of the proposed configuration for white light is higher than 2400:1 at a polar angle of ±60°, irrespective of the azimuthal angle. [ABSTRACT FROM AUTHOR]

We investigated the effect of the polarisation direction and incident angle of a UV light on the electrooptical properties of the polymer-stabilised vertically aligned in-plane switching (PS-VAIPS) liquid crystal. The PS-VAIPS sample cured with a UV light whose polarisation was parallel to the projected direction of the in-plane electric field showed greater transmittance, faster rising time and slower falling time than the sample cured with a UV light with a perpendicular polarisation to the electric field. In addition, the PS-VAIPS sample showed slower rising time and faster falling time with increasing incident angle of the UV light. [ABSTRACT FROM AUTHOR]

Three different types of polyols-poly(ethylene glycol) (PEG), poly(propylene glycol) (PPG), and poly(tetramethylene glycol)-with different molecular weights ( Mn) were incorporated into the prepolymer structure, and the effects were examined with regard to the morphology and performance of holographic polymer dispersed liquid crystal. Among them, PEG showing the lowest glass transition temperature ( Tg) exhibited the lowest threshold voltage ( Vth), lowest operating voltage ( Vop), and lowest diffraction efficiency with slow grating formation owing to its high viscosity of prepolymer mixture. The Tg decreased with increasing Mn because of the decreased crosslink density and hydrogen bonding, which reduced the anchoring strength, Vth and Vop. PPG400 gave Vth and Vop of approximately 7 and 24 V, respectively, with a contrast ratio of approximately 12. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012 [ABSTRACT FROM AUTHOR]

Spontaneous formation of a chiral structure of a polymer-stabilised achiral nematic liquid crystal with cylindrical geometry was suggested. A structurally achiral planar-radial configuration was converted to a coherently swirling twisted-escaped configuration with long time constant of about 10 h. This deformation is considered to be an energy minimising process and an asymmetrically covered polymer layer on the substrate surface seems to be responsible for the escaping process. By reducing the ultraviolet intensity, both substrates were symmetrically covered with the polymer layers and, consequently, a topologically different bipolar configuration was induced. [ABSTRACT FROM AUTHOR]

[Display omitted] • Our IR film is flexible, ultrathin, thermally-insulated, and transparent. • Our CLC polymer IR film shows high optical transmittance, and low haze. • It significantly reduces the greenhouse gas emissions. • It prevents energy consumption for cooling system and lighting in indoor spaces. • The proposed polymer IR film is a promising candidate for energy-efficient window. Transparent windows that insulate infrared (IR) light entering indoor spaces promise to reduce energy consumption. However, a long-standing challenge for an energy-efficient window is achieving compactness and flexibility simultaneously. In this paper, we report the fabrication of a transparent, flexible, ultrathin, and thermally-insulated IR reflector using a coatable chiral-nematic liquid crystal polymer and polyvinyl alcohol (PVA) as an alignment layer. PVA is transparent, biocompatible, thermostable, noncorrosive, and cost-effective. The fabricated IR reflector shows high optical transparency (∼91%) and low haze (≈9.8%) values in the visible spectrum of light. Moreover, it significantly reduces greenhouse gas emissions by preventing energy consumption for cooling systems and lighting in indoor spaces; specifically, it reduces electricity consumption in indoor spaces for lighting and cooling systems under hot weather conditions. To demonstrate the mechanical stability of the fabricated reflector, many mechanical, flexibility, and bending stability tests were conducted. The results show that our proposed IR reflector is a potential candidate for designing desirable shapes for many applications, such as anti-IR devices and energy-efficient windows, for achieving significant environmental and economic benefits. [ABSTRACT FROM AUTHOR]

We report experimental studies on optical (birefringence, Δn), dielectric (Δε) and bend-splay elastic anisotropies (ΔK = K 33 − K 11) of a few mixtures of two nematic liquid crystals, namely CCH-7 and CCN-47, made of highly polar molecules with identical cores and antagonistic orientation of permanent dipoles. In particular, the polar group (-CN) attached to the bicyclohexane core of CCH-7 is oriented along the longitudinal direction whereas, in CCN-47, it is oriented along the transverse direction. We show that apart from the significant contribution to the optical and dielectric anisotropies, the antagonistic orientation of strongly polar groups plays a crucial role in determining the bend-splay elastic anisotropy. The elastic properties are explained based on a model proposed by Priest, considering the effect of intermolecular association and the resulting length-to-width ratio of the molecules. • Binary mixtures of positive and negative dielectric anisotropy liquid crystals. • Antagonistic orientation of dipoles tends to cancels out their effect. • Antiparallel association increases effective length-to-width ratio of the molecules. • Orientation of dipole moments determines the elastic anisotropy of liquid crystals. [ABSTRACT FROM AUTHOR]

The optimized configurations to use a bistable chiral-splay nematic liquid crystal cell as transmissive and reflective display are calculated using the Mueller matrix method. By numerical calculation, nontwist 0° splay state of bistable states is optimized so that the dark state is completely achieved over the entire visible-wavelength range. Based on the optimized conditions, we have experimentally demonstrated a high-contrast ratio of 200:1 in transmissive display and 40:1 in reflective display without using a wideband retardation film. [ABSTRACT FROM AUTHOR]

Cholesteric liquid crystal elastomers (CLCEs) are unique anisotropic rubbers that can change their structural color in response to various stimuli such as heat, chemicals, electric fields, and mechanical stress. Methods such as anisotropic deswelling and surface alignment have been adopted to prepare CLCEs; however, they have limitations in creating spatially controlled CLCE geometries. In this work, a direct ink writing (DIW)‐based 3D‐printable CLCE that can be prepared by extruding viscous CLC ink is developed through a 3D printer nozzle, followed by photopolymerization. Interestingly, the helical axis is inclined to the printing direction by ≈32° due to a combination of the shear‐induced alignment causes during extrusion and the elongational force generated during deposition onto the substrate. This unusual helical axis distortion leads to both blue and red shifts of the reflection color depending on the direction of observation relative to the printing axis. Notably, the printed CLCE exhibits anisotropic mechanochromism upon stretching, because of the stretching‐direction‐dependent variations in the slant angle of the helical axis. This anisotropic mechanochromism can be harnessed to develop a unique CLCE‐based strain sensor displaying intricate color patterns upon stretching, with significant application potential in encryption, anticounterfeiting, and structural health monitoring. [ABSTRACT FROM AUTHOR]

It is shown theoretically that the directly modulated laser diode, with the modulation frequency of its injection current comparable to the relaxation oscillation frequency, exhibits period doubling route to chaos as the modulation index of current is increased. The effect of spontaneous emission factor on the chaotic behavior in the laser diode is also studied. [ABSTRACT FROM AUTHOR]

We propose a vertical alignment liquid crystal cell controlled by double-side in-plane switching with a positive dielectric anisotropy liquid crystal material. In this structure, the pixel electrodes are interdigital electrodes, which are deposited on the bottom and top substrates parallel to each other. In the voltage-off state, the liquid crystal molecules are vertically aligned under the crossed polarizers; hence the cell appears to be dark. When an in-plane field is applied, the liquid crystal molecules tilt down to the left or right along the field direction, which is at 45° with respect to the input polarizer, giving rise to maximum transmission of the incident light. We fabricated the proposed cells, which show higher transmittance and lower driving voltage compared with the conventional vertical alignment configuration with a positive dielectric anisotropy liquid crystal. The improved electro-optical properties are due to the stronger in-plane field compared with the configuration having one-side electrode. In this device, the response time and viewing angle characteristics are almost the same as the conventional structure. [ABSTRACT FROM AUTHOR]

Considering the surface distribution of polyimide chains, the properties of the unidirectional out-of-plane nematic liquid crystal tilt angle are investigated in view of the van der Waals interaction between nematic liquid crystal molecules and two polyimide layers: the anisotropic upper layer and the isotropic lower layer. The dependence of the pretilt angle upon the thickness of the upper polyimide layer oriented by rubbing is estimated from experiment and theory. Another experimental result shows that the relation between the anchoring energy and the thickness of the polyimide layer could be dependent on lower material. This was also explained in view of the nonretarded van der Waals interaction. [ABSTRACT FROM AUTHOR]

Self-switching smart windows, which can be switched between the transparent and opaque states by ambient conditions, have applications in buildings, automobiles, and switchable sunglasses. In particular, technologies for transmittance control without light scattering are highly desirable owing to their ability to control the throughput of sunlight and solar heat through a window without blocking the view. In this study, a self-shading window based on liquid crystals doped with push-pull azobenzene with a haze-free opaque state for transmittance control is demonstrated. For the realization of the haze-free opaque state (or a low-transmittance state), the isotropic phase was used, which can be induced either thermally or optically. [ABSTRACT FROM AUTHOR]

Asymmetrically anchored liquid crystal (LC) cells have different anchoring energies between the top and bottom substrates. A substrate with patterned electrodes has comparatively weak anchoring energy. Therefore, asymmetrically anchored LC cells exhibit more twisted deformation in the on-state than conventional in-plane switching or fringe-field switching cells. In this study, we introduced asymmetrically anchored LC cells for display and photonic applications. We first introduced asymmetrically anchored LC cells to achieve high transmittance for LC displays. The LC molecules can rotate between the two substrates more easily because one of the two substrates has weaker anchoring energy. This resulted in a significant increase in transmittance. Three-terminal electrodes can be used to provide a vertical trigger pulse to an LC cell, thereby overcoming the delayed turn-off switching of an asymmetrically anchored cell without reducing transmittance. Next, we introduced an adjustable polarisation rotator with an asymmetrically anchored LC cell. To offer optical waveguiding, the arrangement of LC molecules can be controlled into a twisted configuration. During the cover of the wavelength range of 400–800 μm, we confirmed that the proposed LC cell can rotate the polarisation axis of linearly polarised light by up to 90°. [ABSTRACT FROM AUTHOR]

We propose a method for fast switching of vertically aligned (VA) negative liquid crystals (LCs) by hiding the relaxation process of LCs. During the turn-off process, a strong in-plane electric field is applied for a short duration of time instead of relying solely on the slow relaxation of LCs. The LC molecules are rotated to the transmission axis of one of the polarisers by the applied in-plane electric field, resulting in turn-off switching that is 5.8 times faster than that of a conventional VA cell. By applying an overdriving scheme, we experimentally obtained a total response time of 3.3 ms. [ABSTRACT FROM AUTHOR]

In this paper, we introduce technologies for fast switching of nematic liquid crystals (LCs) using three-terminal electrodes. Fast switching of LCs can be achieved by employing a vertical trigger pulse, by applying a vertical bias field, and by random alignment of LCs. [ABSTRACT FROM PUBLISHER]

In an article published in Advanced Functional Materials, Suk‐kyun Ahn and their colleagues discuss the creation of cholesteric liquid crystal elastomers (CLCEs) with slanted helices using direct ink writing. The researchers observed an anisotropic mechanochromic response in the printed CLCEs when they were stretched in relation to the printing direction. This unique property allows for the development of strain sensors that display intricate and programmable color patterns when stretched. The study was conducted by Jihye Choi, Yeongyu Choi, Jin‐Hyeong Lee, Min Chan Kim, Sungmin Park, Kyu Hyun, Kyung Min Lee, Tae‐Hoon Yoon, and Suk‐kyun Ahn. [Extracted from the article]

We propose a single-layered electrode structure using three voltage levels instead of two to achieve high transmittance in an in-plane switching liquid crystal display device. The proposed structure consists of two pixel electrodes and one common electrode. By using three voltage levels, we can generate an in-plane electric field higher than that in a conventional in-plane switching device. We confirmed that by using the proposed structure, the transmittance of a liquid crystal device can be increased from 29% to 35% at a slightly lower operating voltage without using the double-layered electrode structure required for the fringe-field switching mode. The transmittance of the proposed device is higher than that of the fringe-field switching device. [ABSTRACT FROM AUTHOR]

Abstract: This paper investigates the nematic liquid crystal (NLC) alignment on ion beam-exposed zinc oxide (ZnO) films. The ZnO films are deposited by a radio frequency magnetron sputtering. During the deposition of ZnO film, we supplied sufficient oxygen gas for high resistivity and transmittance. The deposited films show a high transmittance of over 90% and high resistivity of over 1010 Ωcm. The ZnO films show a high deposition rate of 26.7Å/min. Images obtained via scanning electron microscopy of the ZnO film surfaces, before and after the ion beam exposure, show that groove patterns are formed being to be parallel to the ion beam exposure direction. LC cells are fabricated with the ion beam-exposed ZnO films. The NLC molecules align parallel to the ion beam exposure direction. The electro-optic and response characteristics of fabricated cells show the possibility of application to liquid crystal displays. [Copyright &y& Elsevier]

A tunable liquid crystal (LC) polarization rotator that can rotate the polarization axis of linearly-polarized broadband light is achieved by using an asymmetrically-anchored negative LC cell. Interdigitated electrodes are used to apply an in-plane field to control the twist angle. The use of the asymmetrical anchoring in the LC cell enables continuous change of the twist angle by increasing the applied electric field. For uniform transmission, we used an LC that has negative dielectric anisotropy to avoid tilting of LC molecules by the vertical component of the electric field. We theoretically and experimentally confirmed that the fabricated LC cell could continuously change the twist angle and rotate the polarization axis of the linearly-polarized broadband incident light. [ABSTRACT FROM AUTHOR]

Chiral photonics has emerged as a key technology for future optoelectronics, such as quantum information and encryption, by making use of photonic waves from enantiomeric structures. An inevitable challenge for realizing such chiral optoelectronics is the development of near‐infrared circularly polarized (NIR CP) light‐sensing photodetectors that convert optical power and circular polarization direction into distinguishable electrical signals. Herein, a simple and promising strategy for high‐performance NIR CP light‐sensing organic phototransistors (NIR CPL‐OPTRs) applicable to highly secure optoelectronic encryption is proposed. By directly assembling a standalone cholesteric liquid‐crystal network film in a thin‐film NIR CPL‐OPTR, remarkable responsivity and distinguishability are achieved. The synergetic effect of amplification of the photocurrent signal by the applied electric field and improved light absorption by the reduced reflection in the multilayered structure leads to high responsivity. As a proof‐of‐concept, the chiral phototransistor arrays are demonstrated as a physically unclonable function device and exhibit enhanced cryptographic characteristics. [ABSTRACT FROM AUTHOR]

Organic light emitting diodes with enhanced external light coupling efficiency are demonstrated by incorporating a polymeric diffraction grating fabricated directly on top of the indium tin-oxide (ITO) electrode. Compared to the previous inorganic diffraction gratings fabricated under the ITO electrode, the polymer grating prepared by convenient lithography facilitates the fabrication process and provides good compatibility with conventional production facilities. In spite of the reduction in the emitting area, the luminance efficiency is improved by 72% by imbedding the polymer grating. The strong scattering of the guided mode enables the device to have negligible wavelength dispersion. [ABSTRACT FROM AUTHOR]

We propose methods to obtain multi-domains with different threshold voltages for vertically aligned liquid crystal displays without additional transistors or capacitors. We exposed an ultraviolet light through a photomask and spatially varied the surface anchoring energy by partially decomposing the polyimide or inducing the adsorption of reactive monomers. The threshold voltage was reduced with smaller surface anchoring, and the reduction of the threshold could be qualitatively interpreted using a model describing a weak anchoring condition. [ABSTRACT FROM AUTHOR]

The bistability in a chiral-splay nematic liquid crystal cell, which is obtained by adding a chiral additive to a splay cell, is proposed. In this letter, we describe a horizontal way of switching between the two states of the bistable chiral-splay cell, one state being characterized by a nontwisted director field with splay, the second state showing a director-field with 180[SUP°] twist. The optimization of the various parameters of the device is described. [ABSTRACT FROM AUTHOR]

We proposed a new method for designing graded index lens using liquid crystal infiltration into annular photonic crystals. Applying an external nonuniform voltage in the transverse direction perpendicular to the direction of light propagation yields different orientation of liquid crystal molecules inside the photonic crystal unit cells. As a result, a gradient refractive index was modulated. We numerically investigate focusing properties of the designed graded index structure using plane-wave expansion and finite-difference time-domain methods. The gradient refractive index profile was adjusted by varying the nonuniform voltage excitations, which consequently altered the focal distance of the graded index structure. A wide tuning range of 1856 nm was achieved for focal distance by the proposed graded index structure. This feature can be implemented for planning a flat lens with tunable focal distance based on electro-optic effect. These achievements may have future applications in some optical devices such as near-field imaging and scanning. [ABSTRACT FROM AUTHOR]

We propose a method to confirm the biaxial phase in thermotropic nematic liquid crystals from measurement of the electro-optic characteristics. The electro-optic transmittance curve shows monotonic decrease to zero in the uniaxial phase but the curve shows a U-shaped behavior (or a monotonic decrease to nonzero transmittance) in the biaxial phase. In a bent-core mesogen 4,4′(1,3,4oxadiazole2,5diyl)dipheptylbenzoate (ODBP-Ph-C7), known to be in the nematic phase at temperatures between 173 and 222 °C, it has been found that its electro-optic curve at 190 °C shows a U-shaped behavior, while the curve at 210 °C shows a monotonic decrease to zero transmittance. We believe that these experimental results confirm the biaxial nature of ODBP-Ph-C7. [ABSTRACT FROM AUTHOR]

We propose a dual mode liquid crystal display (LCD), which can realize dynamic and memory operating LCD modes in a display panel. Horizontal switching and bistable chiral splay nematic LCD modes are used for the dynamic and memory operations, respectively. As the horizontal switching is applied to the dynamic operation, it is possible to use the same LC texture of splay for realizing dark states of both the dynamic and memory operations. Because, for each operation, pixel division is not required in the proposed dual mode LCD, there is no decrease in aperture ratio and resolution. In order to obtain superior display performance for both operations, a wideband half-wave configuration is employed to the proposed dual mode LCD. Due to the wideband configuration, very low light leakages at the dark state and good dispersion characteristics for the entire visible range are obtained. As a result, the proposed dual mode LCD shows a high contrast ratio of over 100:1 for both the dynamic and memory operations. [ABSTRACT FROM AUTHOR]

The authors demonstrate through dark injection space-charge-limited current (DI-SCLC) and trap-free SCLC measurements that an indium tin oxide (ITO)/buckminsterfullerene (C60) electrode can form a quasi-Ohmic contact with N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl) benzidine (NPB). The DI-SCLC results show a clear peak current along with a shift of the peak position as the field intensity varies, implying an Ohmic (or quasi-Ohmic) contact. A theoretical simulation of the SCLC also shows that ITO/C60 forms an Ohmic contact with NPB when the electric field intensity is higher than 30 kV/cm. The Ohmic contact makes it possible to estimate the NPB hole mobility through the use of both DI-SCLC and trap-free SCLC analysis. [ABSTRACT FROM AUTHOR]

Abstract Tristate switching of a liquid-crystal (LC) device among transparent, haze-free dark, and high-haze dark states is presented. In the haze-free dark state, LCs and dye molecules are twisted so that the incident light is absorbed without light scattering. In the high-haze dark state, LCs and dye molecules are randomly oriented by electrohydrodynamic instability so that the incident light is not only absorbed but also simultaneously scattered. Depending on the application, the optical characteristics of the proposed LC device can be tuned by employing an LC material with the appropriate birefringence value. Since the polymer structure is not used, it shows a clear transparent state with little haze. Owing to its simple switching process and excellent optical performance, the proposed LC device is very promising for the development of a multipurpose switchable window, which can be used for energy saving and privacy protection. Highlights • Tristate switching of a liquid-crystal device among transparent, haze-free dark, and high-haze dark states • The proposed LC device can be switched among the three states simply by controlling the applied voltage. • We use an LC device doped with ionic and chiral materials • The optical characteristics can be tuned by employing an LC material with the appropriate birefringence value. • Since the polymer structure is not used, it shows a clear transparent state with little haze. [ABSTRACT FROM AUTHOR]

Abstract A dye-doped LC/polymer light shutter with a polymer structure that is formed using the thermally-induced phase separation (TIPS) method is demonstrated. The TIPS method does not include any chemical reaction, and thus there is no degradation of the dye during the fabrication process. The light shutter can be fabricated quickly because the optical performance is not affected by the cooling time. The fabricated TIPS cell exhibits excellent optical performance, such as a low haze value of 0.5% in the initial transparent state, and a high haze value of 99.1% in the opaque state with a superior black color. This approach can be used for the high image quality of see-through displays using organic light-emitting diodes. Highlights • We report the fabrication of an initially-transparent dye-doped LC/polymer light shutter. • The fabricated cell exhibits very low haze in the initial transparent state, and high haze in the opaque state. • Thermally induced phase separation method has easy fabrication process and reduces the fabrication time. • Our fabricated cell shows superior black color without dye degradation. [ABSTRACT FROM AUTHOR]

Abstract It is well-known that orientational order of nematic liquid crystals (NLCs) is converted during phase transition from the long-range order (LRO) in the nematic phase to the short-range order (SRO) in the isotropic state. Finding the initial temperature range of SRO in the isotropic state can be a challenging issue because most of the physical constants disappear after this phase transition. For the first time, to resolve this issue, we introduced a new method based on the electro-optic Kerr (EOK) effect in NLC mixtures. In this method, the coherence length (ξ), which was qualitatively estimated by employing the pre-transitional temperature (T ⁎) according to the de Gennes phenomenological theory, and the refractive index (n) were correlated with the Kerr constant (B) at the same temperature in the isotropic phase. Because molecular interaction in the NLCs is one of the essential factors in the investigation of the orientational ordering, we used n and ξ as described intra- and intermolecular interactions, respectively. In other words, n attributes to the polarization and dipole moment as an important parameter of the intramolecular interaction and ξ demonstrates the intermolecular interaction and domains of SRO interaction in the isotropic phase. Finally, the initial temperature range of SRO in the isotropic phase was found from the temperature dependence with B of the normalized values of influential coefficients n and ξ at the similar temperatures. Our proposed method appropriately can provide a suitable approach to distinguish the preservation of the anisotropy effect in the isotropic phase of NLCs. Graphical abstract Unlabelled Image Highlights • Initial temperature range of SRO defined in isotropic phase of NLC by electro-optical Kerr effect. • The ξ and refractive index (n) were correlated with B at the same temperature in the isotropic phase. • The proposed approach distinguishes preservation of anisotropy effect in isotropic phase of NLC. [ABSTRACT FROM AUTHOR]

Abstract Transmittance-control liquid crystal (LC) devices require a high transmittance difference between their transparent and opaque states. Dye-doped cholesteric LC (CLC) cells have been widely used for transmittance control because they provide the highest transmittance difference among LC modes. However, the color of a CLC cell is different from that of a homogeneously-aligned LC cell. In this paper, we present a systematic approach to find the optimal dye concentrations for the desired black color in a dye-doped CLC cell. To achieve the desired black color in a dye-doped CLC cell, we consider its transmission spectrum in our numerical calculations. The optimal concentration for each individual dye is found through an iterative process. We demonstrate that a dye-doped CLC cell designed by considering its transmission spectrum can provide a true black color in the CIE 1931 color space. Highlights • We present a systematic approach to find the optimal dye concentrations for the desired black color in a dye-doped CLC cell. • It offers an effective method for the fabrication of transmittance-control LC device. • To find the optimal dye concentrations, we considered the transmission spectrum of a dye-doped CLC cell. [ABSTRACT FROM AUTHOR]

Abstract The temperature dependence of optical birefringence, order parameter, effective geometry parameter, and normalized polarizability was determined for nematic liquid crystal mixtures by measuring the refractive indices. The effects of the adjustable parameters obtained from temperature-dependent refractive indices were analyzed appropriately for the crossover temperature and order parameter values. Besides, a four-parameter power law expression method was used for the optical birefringence measurement to address inappropriate fits in the weak first-order phase transition region. From this method, the effective second order phase transition temperature T ⁎⁎ was determined by showing the slightly higher values than phase transition temperature. The value of the order parameter critical exponent λ obtained from this method showed a good agreement with the mean field theory by demonstrating closeness to the tricritical hypothesis (β = 0.25). As a consequence, the measurement of the temperature-dependent optical birefringence was successfully verified the pre-transitional phenomena accurately, and it can facilitate an insightful description of that region. Graphical abstract Unlabelled Image Highlights • Temperature dependence of high birefringence (∆ n) liquid crystals was analyzed. • The temperature dependent order parameter was sorted based on ∆ n values. • Lower (∆ n) o and β values were valuable factors for increasing T co at the same T NI. • A four-parameter power law expression shows the high critical exponent value. [ABSTRACT FROM AUTHOR]

In this paper, we present the effects of curing temperature on switching between the transparent and translucent states in a polymer-stabilized liquid-crystal (PSLC) cell. When cured at a low temperature, polymer structures are formed without disturbing the initial alignment of LCs so that haze in the transparent state is dramatically reduced. Moreover, we can achieve very fast switching between the haze-free transparent and high-haze translucent states because there is a little degradation in the performance of the transparent and translucent states when the polymer concentration is increased. We demonstrated an ON–OFF response time of less than 3 ms and a gray-to-gray response time of less than 6 ms in a PSLC cell. [ABSTRACT FROM AUTHOR]

We report a method to control the haze value by dynamic scattering in a liquid crystal mixture without ion dopants. The liquid crystal (LC) mixture consists of chiral smectic C (SmC*) and nematic (N) LC molecules. In the absence of an electric field, LC molecules in the SmC* phase are oriented by the neighboring vertically-aligned N-LC molecules so that the LC cell is transparent. When a vertical electric field is applied to the LC cell, N-LC molecules with negative dielectric anisotropy tilt down in a random direction parallel to the two substrates, whereas SmC*-LC molecules are rotated with the polarity reversal of the applied field. During the switching process, we observed dynamic scattering because the random orientation of N-LCs is maintained via the rotation of SmC*-LCs, resulting in a high-haze translucent state without the use of ionic dopants. The LC mixture exhibited a very high haze of 96.1% in the translucent state while maintaining the haze-free (<1%) transparent state owing to the use of an LC layer without a polymer structure. [ABSTRACT FROM AUTHOR]

We report control of the haze value in a liquid crystal (LC) cell driven by a fringe electric field. When a fringe field is applied to a vertically aligned (VA) cell, a large spatial phase difference with a short grating period is induced in the LC layer. The average grating period of a VA cell driven by a fringe field is a quarter of the pitch of the interdigitated electrodes, which is half of the grating period of a VA cell driven by an in-plane field. Moreover, a sharper spatial phase profile is built around the edges of the interdigitated electrodes, which led to a high haze of 84.3% in the translucent state. The device was haze-free in the transparent state owing to the use of an LC layer without a polymer structure. To increase the haze value of the LC device while retaining a short response time, we developed an LC cell with crossed interdigitated electrodes where a large spatial phase difference is induced with little dependence on the azimuth angle. By applying a fringe electric field to a 20 μm thick LC cell using crossed interdigitated electrodes, we demonstrated a very high haze of 95.4% and a response time of less than 5 ms. [ABSTRACT FROM AUTHOR]

A dye-doped cholesteric liquid crystal (LC) cell with the focal-conic initial state is demonstrated. Although dye-doped LC/polymer composites have been widely used for LC light shutters, dye-doped LC cells with polymer structures suffer from the degradation of dichroic dyes during the UV curing process. To avoid this problem, we propose a dye-doped cholesteric LC cell using vertical alignment layers instead of polymer structures. We have shown that the focal-conic initial state can be obtained by homeotropic anchoring without the polymer structure. The proposed device not only provides the black color but can also hide objects behind a display panel in the focal-conic initial state without the degradation of dichroic dyes. [ABSTRACT FROM AUTHOR]

We demonstrate an ion-doped liquid-crystal (LC) cell that can provide a very low specular transmittance in the opaque state using the electro-hydrodynamic effect. In the opaque state, the LC and dye molecules are oriented randomly in planes parallel to the substrates because of the electrohydrodynamic effect. We found that the total transmittance of an ion-doped LC cell is almost the same as that of a light shutter based on light absorption and its haze value is the same as that of a light shutter based on light scattering. Moreover, an ion-doped LC cell can be fabricated without an ultraviolet curable process. Owing to its excellent opaque state properties, an ion-doped LC cell can be used in see-through display and smart-window applications. [ABSTRACT FROM AUTHOR]

In this paper, we present a diffractive liquid crystal (LC) device capable of rapid switching between the transparent and translucent states for window display applications. In contrast to previously reported LC light shutters based on light scattering, the proposed LC device relies on diffraction of white incident light by an electric field-induced periodic continuous LC profile. It can be switched between the transparent and translucent states without a complicated driving scheme or a polymer structure. This device exhibits outstanding features for window display applications, such as a high transparency and a wide viewing angle in the transparent state, a low operating voltage, and a short response time. [ABSTRACT FROM PUBLISHER]

Pretilt angle measurable by using the conventional crystal rotation method is limited to about 0°-20° and 700-90°. We propose a method by which we can measure the pretilt angle by using the crystal rotation method even if the pretilt angle is between 20° and 70°. In this method, the determination of a pretilt angle is achieved by finding the rotation angles where transmittances are maximum and minimum in the periodic transmittance characteristics obtained with the variation of rotation angle. [ABSTRACT FROM AUTHOR]

We report a thermal curing method for fabrication of a dye-doped polymer-stabilized liquid crystal (PSLC) light shutter, which can prevent the decrease in absorption and discoloration of the dye caused by the UV curing process. We found that the measured transmittance in the opaque state of a dye-doped PSLC cell fabricated by thermal curing was approximately 35% lower than that of a dye-doped PSLC cell fabricated by UV curing. Thermal curing can be an alternative approach for fabrication of a dye-doped PSLC light shutter which can be used to provide high visibility of a see-through display. [ABSTRACT FROM AUTHOR]

We fabricated a light shutter using plastic substrates for high visibility of a flexible see-through display. To achieve a flexible light shutter using liquid crystals (LC), it is essential to maintain the cell gap when the light shutter is bent. We studied methods to fabricate flexible LC light shutters using plastic substrates. We demonstrated light shutters that are initially transparent and flexible with or without polymer walls. We have elucidated that polymer walls and networks provide mechanical stability against the bending of an LC light shutter without any degradation in the electro-optic characteristics. We predict that a flexible light shutter provides not only high visibility but also mechanical stability to a flexible see-through display by positioning it at the back of a flexible see-through display panel. [ABSTRACT FROM AUTHOR]

By switching a light shutter placed at the backside of a see-through display, we can select the transparent or high-visibility mode of the display panel. In this paper, we introduce technologies for liquid crystal (LC) light shutters that can scatter and absorb the incident light simultaneously, which is preferable for display applications. A light shutter for display applications can be realized in the normally-opaque mode by using a double-layered structure using cholesteric LCs or a single-layered structure using dye-doped cholesteric LCs. Whereas, it can be realized in the normally-transparent mode by using dye-doped polymer-networked LC cells using negative or positive LCs. Operation of each of the technologies is reviewed and the performance of these technologies is compared in this paper. [ABSTRACT FROM AUTHOR]

A light shutter, which consists of a dye-doped cholesteric liquid crystal (ChLC) layer and a polymer-dispersed liquid crystal (PDLC) film, for simultaneous control of haze and transmittance is demonstrated. In the opaque state, it can not only provide a black color by using the dye-doped ChLCs but also hide the objects behind the display panel by using the PDLC film. The proposed light shutter shows a high haze value of 90.7% with a low specular transmittance of 1.20%. By switching the proposed light shutter placed at the back of a see-through display, we can choose between the see-through mode and the high-visibility mode in a see-through display. [ABSTRACT FROM AUTHOR]

Low-frequency driving of a liquid crystal display (LCD) panel to minimise power consumption has drawn much attention recently. In case an LCD panel is driven by a low-frequency fringe field, image flickering phenomenon is detected by the naked human eye when the sign of the applied electric field is reversed. We investigated the effect of electrode spacing on the image flickering phenomenon induced by the flexoelectric effect in a fringe-field-switching (FFS) liquid crystal cell. We found that the image flicker in an FFS cell under low-frequency driving can be eliminated in a simple manner by changing the electrode spacing. [ABSTRACT FROM PUBLISHER]

We propose a homogeneously aligned liquid crystal (LC) cell with double-side protrusion electrodes for fast response and low-voltage operation. In the proposed device, both the bottom and top substrates have pixel electrodes to generate the fringe electric field. Because the penetration depth of the electric field is increased owing to the protrusion electrodes, the operating voltage is very low and the turn-on time is dramatically reduced compared with the conventional in-plane switching (IPS) mode. Moreover, LC molecules anchored strongly to the penetrated protrusion electrodes on both substrates exert a strong restoring force, resulting in a fast turn-off time. We found that the total response time of the LC cell with the proposed structure is three times faster than that of the conventional IPS mode. [ABSTRACT FROM AUTHOR]

We propose a light shutter device using dye-doped cholesteric liquid crystals for a high-visibility see-through display. In the focal-conic state, the proposed device can perfectly block the background image through simultaneous use of light scattering and absorption effects in a single-layered structure. By switching the proposed device placed at the backside of a see-through display, we can choose transparent or high-visibility display modes in a see-through display. [ABSTRACT FROM PUBLISHER]

We found that we can increase the transmittance of a liquid crystal (LC) cell by doping the alignment material with nanoparticles. We fabricated an LC cell using indium–tin–oxide glass substrates coated with SiO2-doped polyimide. We confirmed that the transmittance of LC cells fabricated using SiO2-doped polyimide was higher than that of LC cells fabricated using pure polyimide. To account for the increase of transmittance, we measured the order parameter of the fabricated LC cells and investigated the surface morphology of the alignment layer using atomic force microscopy. [ABSTRACT FROM PUBLISHER]