Homogeneous Liquid Crystal Research Articles

Homogeneous self-aligned liquid crystals on wrinkled-wall poly(dimethylsiloxane) via localised ion-beam irradiation.

We demonstrate self-aligned liquid crystals (LCs) using a wrinkled-wall polydimethylsiloxane (PDMS) wrinkle structure, which is a key factor to obtain a stable homogeneous alignment state with positive LCs. We constructed the wrinkled walls via localised surface exposure to IB radiation, which passed through a long length localised pattern mask. The creation of the wrinkled wall helped to align the LC molecules homogeneously because the wrinkled wall acted as a guide for the arrangement of positive LC molecules. In addition, we confirmed the stability of the alignment state as the width of the wrinkled wall was changed. Although this wrinkled-wall method is a non-contact method, LC alignment is achieved via an anisotropic topographical guide, which provides the LC molecules with stable homogeneous alignment.

Photoalignment behaviour on polystyrene films containing chalcone moieties

A series of polystyrene derivatives containing chalcone (one of the biological compounds) side groups, poly(4-(4-vinylbenzyloxy)chalcone) (PCHAL#), where # is the molar content of chalcone using polymer modification reactions, were prepared in order to study the effect of the chalcone side groups on the liquid crystal (LC) alignment properties. The LC alignment behaviour of the polymer was investigated using photoalignment method. The LC cells made from photoirradiated PCHAL# films exhibited homogeneous planar LC alignment with an extremely low pretilt angle of approximately 0°. We found that LC aligning ability of the LC cells made from photoirradiated PCHAL# films was affected by the molar content of chalcone side groups. For example, the azimuthal anchoring energy of a PCHAL100 (9 × 10−6 J/m2) was found to be much larger than that of PCHAL18 (5 × 10−7 J/m2). In addition the electro-optical characteristics of the LC cells fabricated with PCHAL100 films such as threshold voltage, driving voltage, and response time were as good as those fabricated from rubbed polyimide films, the most commonly used LC alignment layers.

Enhanced Electro-Optical Properties of Electrically Controlled Birefringence Cells on Solution-Derived Lanthanum Oxide Films Treated with Ion Beam Irradiation

Herein we demonstrate the improved performance of electrically controlled birefringence (ECB) cells fabricated on solution-derived La2O3 films pre-treated with ion beam irradiation. Treatment by an ion-beam (IB) irradiation system and appropriate annealing temperature allowed La2O3 surfaces to support homogeneous liquid crystal (LC) alignment. The EO characteristics of the aligned homogenous LCs and ECB modes in cells fabricated on La2O3 layers were comparable to those of cells fabricated on polyimide, and IB-irradiated La2O3 film surfaces showed good potential for use as an alignment layer.

Liquid Crystal Alignment Behaviors of Polystyrene Derivatives Containing Coumarin Moieties

We synthesized a series of polystyrene derivatives containing coumarin side groups, poly(7-(4-vinylbenzyloxy)coumarin) (P7COU#) and poly(7-(4-vinylbenzyloxy)4-phenylcoumarin) (P7COU4P#), where # is the molar content of 7-hydroxycoumarin and 7-hydroxy-4-phenyl coumarin, respectively, using polymer analogous reaction, in order to study the effect of the 7-hydroxycoumarin and 7-hydroxy-4-phenyl coumarin side groups on the liquid crystal (LC) alignment properties. The LC alignment behavior of these two series was investigated by photoalignment or rubbing alignment. The LC cells made from photoirradiated P7COU# and P7COU4P# films showed homogeneous planar LC alignment. We found that LC aligning ability of the LC cells made from rubbed P7COU# and P7COU4P# films were affected by the structure and molar content of coumarin side groups. For example, anchoring energy of the LC cell fabricated with rubbed P7COU82 (7 × 10−5 J/m2) and P7COU4P81 (7 × 10−7 J/m2) film was increased drastically and slightly compared to polystyrene (10−7−10−8 J/m2), respectively. Particularly, anchoring energy of the LC cell made from rubbed P7COU# having more than 51 mol % of the 7-hydroxycoumarin as a side groups is comparable to that of the conventional polyimide in the LCD industry.

High performance twisted nematic liquid crystal display with solution-derived YZO surface modification via ion-beam irradiation.

Solution-derived YZO films were investigated as liquid crystal (LC) alignment layers modified by ion beam (IB) irradiation. Solution processing was adopted in place of the sputtering method for the deposition of YZO films as LC alignment layers. Uniform and homogeneous LC alignment was achieved to produce a high performance LC system. X-ray photoelectron spectroscopy analysis showed that surface reformation of YZO films by annealing and IB irradiation affects the uniformity of the LC alignment. Superior electro-optical characteristics of twisted nematic LC cells constructed from IB-irradiated YZO films were observed, which indicates that the proposed solution-derived YZO films have strong potential for use in the production of advanced LC displays.

High Performance of the Electrically Controlled Birefringence Mode in Solution-Derived La2O3 Film Using Low Temperature

We demonstrated the electro-optical characteristics of multi-stacked solution-derived La2O3 films in low temperature. Uniform and homogeneous liquid crystal (LC) alignment was achieved, and the films showed high performance. The electro-optic characteristics of the electrically controlled birefringence (ECB) mode with La2O3 layers were comparable to layers derived from polyimide, which indicated that La2O3 film had potential as an alignment layer due to its low threshold voltage (1.70 V) and fast response time (3.17 ms). The LC alignment on the solution-derived La2O3 surfaces was attributed to Van der Waals forces between LC molecules and La2O3 films. X-ray photoelectron spectroscopy demonstrated that the number of layers of coating changed the chemical structure, thereby shifting the binding energy and altering the bonding intensity.

Polystyrene Blend Alignment Layers for Pretilt Angle Control of Liquid Crystal

We prepared blend alignment layer based on polystyrene containing 7-hydroxycoumarin (P7COU) and polystyrene containing 2-naphthoxy (P2NAP) side groups for liquid crystal (LC) alignment. The LC cells made from the rubbed P7COU/P2NAP blended films exhibited a shift of the LC alignment direction by approximately 20° compared with those made from a polystyrene film. Stable and homogeneous planar LC cells having pretilt angles adjustable from 0° to 5° were obtained from these polymer films having molar contents of P7COU and P2NAP in the ranges of 100–80 and 0–20 mole%, respectively. The LC alignment behavior was well correlated with the wettability of the polymer films.

The interaction of colloidal particles with weak homeotropic anchoring energy in homogeneous nematic liquid crystal cells

We have investigated interactions of colloidal particles with weak homeotropic anchoring energy in homogeneous nematic liquid crystal cells. Particle-wall and inter-particle interactions were observed experimentally and analyzed using typical dipole-dipole and quadrupole-quadrupole interactions, including substrate effects as the image charges. Both experimental results matched well with the calculated results for the effective particle radius reflecting the weak anchoring. The effective radius is reduced by the amount of extrapolation length than the actual particle radius. The effective radii of polyethylene micro-particles were reduced to a coefficient ζ (0.78 ≥ ζ ≥ 0.52) times the actual radius with anchoring coefficients in the range of 3.8 × 10(-6) to 1.4 × 10(-6) J m(-2). The anchoring energy of the particles is, therefore, a key component for explaining liquid crystal colloidal systems.

Liquid Crystal Microlens Array Using Double Lenticular Electrodes

A liquid crystal (LC) microlens array using double lenticular electrodes is proposed. Two identical substrates with a lenticular electrode on each surface are prepared. The two lenticular electrodes are placed in parallel position with a gap. When a voltage is applied across the electrodes, a periodically inhomogeneous electric field can be generated. Such an electric field can cause a homogeneous LC with a gradient refractive index distribution. Our experiment results show that the lens cell can present good focusing property. The shortest focal length (~ 1.1 mm) of the lens cell can be obtained at a low operating voltage (18 Vrms).

Liquid crystal orientation on solution processed zinc oxide inorganic films according to molecular concentration

In this paper we present the characteristics of molar concentration-dependent zinc oxide (ZnO) inorganic films deposited by the solution process for application in liquid crystal displays. ZnO surfaces supported homogeneously aligned liquid crystal (LC) molecules based on an ion-beam (IB) irradiation system. Uniform LC alignment was obtained at ZnO molar concentrations greater than 0.25moll−1. X-ray photoelectron spectroscopic (XPS) analysis revealed that changes in the orientation of LC molecules occurred on the ZnO layer. The electro-optic characteristics of the aligned homogenous LCs and twisted nematic (TN) mode based on the ZnO layer were comparable to those based on polyimide, which showed good potential as ZnO surfaces as an alignment layer.

Paper No 15.4: A Working Prototype of Flickerless Full‐Screen Resolution Autostereoscopic Display With Simultaneous Reproduction of Two Image Elements in One Display Pixel

AbstractThe design and key components of working prototype of the flat autostereoscopic display with full‐screen resolution for each of the two image views of 3D scene are presented. Simultaneous reproduction of two image elements in one display pixel is implemented using polarization coding by standard liquid crystal (LC) matrices. Polarization decoding of two image elements is implemented by static phase‐polarization parallax barrier based on column‐addressed twist or homogeneous birefringent LC structures. Stereoscopic image flicker is absent even at 60 frame rate. Although autostereoscopic image is observed only by a single user in definite viewing zones, the same display design allows to observe stereoscopic images by many users wearing passive polarization glasses (if to switch off the parallax barrier and to remove the output polarizer sheet).

Adjustable Bistability and Hysteresis Loop in a Nd:GdVO4 Laser with an Intracavity Liquid Crystal Cell

Adjustable optical bistability and spatial hysteresis appearing in a Nd:GdVO4 laser with an intracavity liquid crystal (LC) cell were achieved. On the basis of optically induced LC reorientations and the varying magnitude of the order parameter, two types of LC were used to easily control the characteristics of hysteresis with a single control variable. Using an electrically driven twisted-nematic LC, an adjustable hysteresis area as well as a switching-on pump power was demonstrated and periodic spatiotemporal patterns were observed. By contrast, amplified hysteresis loops were obtained by increasing the rotation angle of homogeneous LC cells with a nearly invariable switching-on pump power.

Liquid crystal phase shifters with a twist

The phase-shift per unit-length of microwave radiation passing through a liquid crystal cell is calculated. By using twisted nematics, as compared to the standard homogeneous nematic liquid crystal, the phase-shift per unit-length is increased over the transition region. This has the potential to lower the operating voltage and decrease the size of such phase shifters. In particular, the phase shifts for microwave radiation produced by the liquid crystals K15, E7, and E44 are calculated. It is found that liquid crystals with large values of the elastic constant ratio K22/K11 have their performance most improved when a twist is introduced.

Measurement of the liquid crystal pretilt angle in cells with homogeneous and inhomogeneous liquid crystal director configuration

Optical and electro-optical methods of liquid crystal (LC) director pretilt angle measurement are described for LC cells with homogeneous and inhomogeneous LC director distribution. The LC pretilt on both LC substrates can have the same or opposite direction. The phase retardation difference of both extraordinary and ordinary polarized rays passing through an LC cell with homogeneous and inhomogeneous LC director distribution has been calculated versus the LC pretilt angle θ(0) on the cell's substrates in the range 0≤θ(0)≤90°. The experimental procedure for phase retardation difference determination by measurement of the LC cell transmission between crossed polarizers for cells with LC tilted alignment is described. The method developed can also be used in optical compensator design.

Superior electro-optic properties of liquid crystal system using cobalt oxide nanoparticle dispersion

In this article, we study the electro-optical (EO) properties of the homogeneous aligned nematic liquid crystal (N-LC) doped with cobalt oxide (Co3O4) nanoparticles (NPs). The EO characteristics of Co3O4 doped N-LC are higher performance, indicating lower threshold voltage (1.33 V), faster rising time (1.479 ms), and faster falling time (9.343 ms) than pure liquid crystal (LC) cells. We have demonstrated these results by investigating the relationship between dielectric constants and LC device properties. Furthermore, we proved NPs doped N-LC cells drive low power operation without capacitance hysteresis. Our experimental results were verified by software simulation based on general physical properties.

Phase retardation vs pretilt angle in liquid crystal cells with homogeneous and inhomogeneous LC director configuration

Phase retardation of both extraordinary and ordinary polarized rays passing through a liquid crystal (LC) cell with homogeneous and inhomogeneous LC director distribution is calculated as a function of the LC pretilt angle θ₀ on the cell substrates in the range 0 ≤ θ₀ ≤ 90°. The LC pretilt on both substrates can have the same or opposite direction, thereby forming homogeneous, splay, or bend director configurations. At the same pretilt angle value, the largest phase retardation ΔΦ is observed in splay LC cells, whereas the smallest phase retardation is observed in bend cells. For the θ₀ values close to 0, 45°, and 90°, analytical approximations are derived, showing that phase retardation depends on LC birefringence variation.

Chirally Homogeneous and Heterogeneous Dendritic Liquid Crystals

We have coupled methyl α-d-glucoside (G) and methyl α-d-mannoside (M) as the chiral structural variant moieties in the core and at the branching sites within dendritic scaffolds surrounded by 12 cy...

Application of Magnesium Fluoride $(\hbox{MgF}_{2})$ Thin Films for Liquid Crystal Alignment Using Ion-Beam Irradiation

This letter introduces the characteristics of the magnesium fluoride ( MgF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) inorganic film deposited by an electron-beam evaporation system for liquid crystal display (LCD) applications. We first achieved homogeneous liquid crystal (LC) alignment by controlling the ion-beam (IB) irradiation energy intensity. We also showed that MgF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> is more transparent than spin-coated polyimide (PI) in the visible wavelength. By chemical analysis, IB irradiation selectively broke the Mg-F bonding structure because of the IB energy intensity; thus, the MgF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> surface was turned to an unstable MgF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2-x</sub> surface, resulting in homogeneous LC orientation. Moreover, the electrooptic characteristics of a homogeneously aligned twisted nematic (TN)-LCD on the MgF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> layer showed good performance as the TN-LCD on the polyimide, showing a strong possibility of the MgF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> material as an LC alignment layer.

Surface reformation on solution-derived zinc oxide films for liquid crystal systems via ion-beam irradiation

We investigated solution-derived ZnO films as liquid crystal (LC) alignment layers via ion-beam (IB) irradiation. Solution processing was adopted to replace the sputtering method for the deposition of ZnO films as LC alignment layers. Uniform and homogeneous LC alignment was achieved, and a high-performance LC system was achieved using these substrates. X-ray photoelectron spectroscopy (XPS) analysis showed that surface reformation of ZnO films by annealing and IB irradiation affects the uniformity of the LC alignment and allows control of the pretilt angle. Superior electro-optical (EO) characteristics of twisted nematic-LC cells constructed with IB-irradiated ZnO films were observed, which indicates that the proposed solution-derived ZnO films have strong potential for use in the production of advanced LC displays.

Electro-Optical Characteristics of ZrO2 Nanoparticle Doped Liquid Crystal on Ion-Beam Irradiated Polyimide Layer

It is well known that doping liquid crystals (LCs) with nanoparticles can readily change the physical and electro-optical properties of LC mixture. In this paper, we report on how the electro-optical properties and thermal stability of an LC system were enhanced by dispersing zirconia (ZrO2) nanoparticles in nematic LCs on ion-beam irradiated polyimide layers. Homogeneous LC alignment was achieved and ZrO2/LC mixture was applied in twisted-nematic (TN) mode. The addition of ZrO2 nanoparticles contributed to improvement of electro-optical properties in the TN LC cell by lowering voltage operation and decreasing response time. The TN LC cells with a ZrO2 nanoparticle concentration of 2.0 wt% showed the lowest threshold voltage of 2.0 V and the fastest response time of 15.3 ms. This enhanced electro-optical performance was likely due to van-der waals interactions and the screening effect of the ZrO2 nanoparticles in the LC medium. The thermal stability of the ZrO2/LC mixture was also improved compared to a pristine LC system.