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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]

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 an optical configuration for a nematic liquid crystal (LC) device that is switchable between the reflective and the transmissive modes. By placing a reflective polarizer between the two LC layers, we obtain higher reflectance and reduce the parallax effect in the reflective mode. We can eliminate the parallax effect by using a wire-grid polarizer or other in-cell reflective polarizers. We expect that the proposed device can be used in various outdoor applications. [c] 2010 Optical Society of America OCIS codes: 230.0230, 230.3720.

We propose an optical configuration of a twisted nematic liquid crystal device driven by a fringe field for a single-cell-gap transflective display. The dark state of the reflective part is realized by a nematic liquid crystal layer with a twist angle of 63.6[degrees] and retardation of 194 rim, while a quarter-wave plate is inserted for the dark state of the transmissive part. Wavelength dispersion of the liquid crystal layer is suppressed by introducing a half-wave plate. Different directions of electric fields rotate liquid crystals to 15[degrees] for the bright state of the reflective part, but to -30[degrees] for that of the transmissive part. With the proposed configuration, we can realize a high-brightness single-gamma transflective display in a single-cell-gap structure without any in-cell retardation layers. OCIS codes: 230.0230, 230.3720.

As a new alternative countermeasure to riprap for scour protection around bridge piers, wire gabions were investigated experimentally for failure mechanisms, effects of significant parameters on failure and its sizing in a clear-water condition. The dominating failure mechanism was found to be a shear failure. Based on the experimental data, the controlling factors for the stability of wire gabions as a scour countermeasure at the pier are flow depth relative to pier diameter, length to thickness ratio, coverage, alignment and placement depth of wire gabions. An equation for sizing of a wire gabion is proposed in terms of Froude number and factors reflecting both the effect and limit of significant parameters. Comparison of the equation with those of ripraps shows that smaller wire gabions than ripraps provide an equivalent protection implying cost effective and improved stability. DOI: 10.1061/(ASCE)0733-9429(2005)131:11(942) CE Database subject headings: Bridges, piers; Gabions; Riprap; Scour; Shear failure; Stability.

A numerical model based upon a second-order upwind finite volume method on unstructured triangular grids is developed for solving shallow water equations. The HLL approximate Riemann solver is used for the computation of inviscid flux functions, which makes it possible to handle discontinuous solutions. A multidimensional slope-limiting technique is employed to achieve second-order spatial accuracy and to prevent spurious oscillations. To alleviate the problems associated with numerical instabilities due to small water depths near a wet/dry boundary, the friction source terms are treated in a fully implicit way. A third-order total variation diminishing Runge-Kutta method is used for the time integration of semidiscrete equations. The developed numerical model has been applied to several test cases as well as to real flows. Numerical tests prove the robustness and accuracy of the model. CE Database subject headings: Floods; Hydraulic models; Numerical models; Shallow waters; Unsteady flow.

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]

A self‐regulating liquid crystal (LC) smart window whose reflectance can be controlled by ambient conditions is demonstrated. Thermally‐ or optically‐induced switching between the transparent state and a near‐infrared (NIR) reflective state can be used for energy‐saving windows. Reflection of NIR can reduce the energy used for cooling while remaining transparent to visible light. [ABSTRACT FROM AUTHOR]

Reported herein is a method for the formation of a polymer structure on a plastic substrate through the phase separation of a liquid crystal mixture. Polymer walls can be formed on a specific location through phase separation induced by a spatial differences in elastic energy and electric field intensity. The fabricated polymer walls were observed through various methods. The measured aspect ratio of the fabricated polymer walls was about 12.9, with a 10.3 μm height and a 0.8 μm width. [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]

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]

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 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]

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]

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]

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]

Properties of nematic liquid crystals aligned on polyimide surfaces exposed to a low-energy Ar ion beam are investigated. The study revealed that there are few ions or radicals induced by broken bonds on polyimide surfaces bombarded with Ar ion beams.

We report a bistable smectic‐A (SmA) liquid crystal (LC) cell with crossed interdigitated electrodes. An SmA‐LC cell with crossed interdigitated electrodes is switchable between haze‐free transparent and high‐haze translucent states. It can be operated with very little power because it consumes power only while the state is being switched. Owing to the high diffraction efficiency, it can provide a high haze value of 92.2% in the translucent state. It has shown a clear transparent state with little haze and excellent optical characteristics in the translucent state. We expect that the device will be used for a window display application. [ABSTRACT FROM AUTHOR]

Autonomous stimulus-responsive polymer-stabilized cholesteric liquid crystals (PSCLCs) are promising materials for various applications. In this work, a PSCLC cell whose wavelength of selective reflection changes autonomously according to the temperature or can be controlled by applying an electric field was fabricated by using ultraviolet (UV) light absorbers. The UV light absorbers in the PSCLC cell are used not only for preventing the degradation of the substrate but also for stabilizing the polymeric network by converting the harmful UV radiation into harmless heat. To achieve the optimum conditions, different types of UV light absorbers were examined at various concentrations and UV light intensities. The results revealed that the benzophenone-type UV absorbers provide an extensive blue-shift tuning of the Bragg reflection in the PSCLC. By determining the molar extinction coefficient (ε) values, which provide a measure of UV light absorption at a given wavelength, at three important wavelengths―the maximum absorption wavelength (λmax) of the UV absorbers, λmax of the photoinitiator (345 nm), and the UV lamp wavelength (365 nm)―the UV light intensity gradient throughout the cell was defined. Reduction of the ε value indicates a sharp drop in the UV light intensity within a PSCLC cell. This phenomenon leads to the diffusion of reactive mesogens towards the UV lamp side of the cell to achieve a tight pitch gradient and extensive blue-shift tuning of the selective reflection. [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 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]