A single-cell-gap transflective liquid crystal display with a vertically aligned cell

A single-cell-gap transflective liquid crystal display with a vertically aligned cell using square ring electrode is demonstrated. The top substrate has a top planar common electrode, a square ring pixel electrode is coated on the bottom substrate, while a bumpy reflector is coated under the bottom substrate. In this device, the planar common electrode and square ring pixel electrode generate a strong longitudinal electric field in the transmissive region (T region) and a weak fringe field in the reflective region (R region). As result, the T and R regions accumulate the same optical phase retardation. The simulation results show that the display exhibits reasonably low operating voltage, high transmittance and well-matched voltage-dependent transmittance and reflectance curves. Besides, fabrication process of the transflective liquid crystal display is very simple.     

A transflective polymer-stabilised blue-phase liquid display with partitioned wall-shaped electrodes

A transflective polymer-stabilised blue-phase liquid crystal display (BP-LCD) with partitioned wall-shaped electrodes is proposed. The etched polymer layer contributes to balance the optical phase retardation between transmissive (T) and reflective (R) regions. The partitioned wall-shaped electrodes generate uniform and horizontal fields throughout the entire LC layer to induce isotropic-to-anisotropic transition in the blue-phase liquid crystal medium through Kerr effect. Consequently, the accumulated phase retardation along beam path is large, resulting in reasonable low operation voltage and high transmittance both in T and R regions. This approach enables the BP-LCD to be addressed by amorphous silicon thin-film transistors. Moreover, it exhibits wide viewing angle and a well-matched gamma curve.     

Transflective blue-phase liquid crystal display with polar opposite electrodes

A submillisecond response, wide view and single-cell-gap transflective (TR) display employing a blue-phase liquid crystal is proposed. The device employs polar opposite in-plane switching (IPS) electrodes. To balance the optical phase retardation between transmissive (T) and reflective (R) regions, the IPS electrodes are formed with unequal gaps in the two regions. This display exhibits reasonably high optical efficiency and well-matched voltage-dependent transmittance and reflectance curves.     

A simple transflective liquid crystal display with composite dielectric layer

ABSTRACT

A simple transflective liquid crystal display with a vertically aligned cell using a composite dielectric layer is demonstrated. The top substrate has a top planar common electrode, two transparent dielectric layers with different dielectric constants are coated on the bottom planar pixel electrode to generate linearly varying electric potential from the transmissive region (T region) to the reflective region (R region), while two bumpy reflectors are coated under the bottom substrate. In this device, with the composite dielectric layer, the common and pixel electrodes generate a strong electric potential in the T region and a relatively weak electric potential in the R region. Consequently, the T and R regions accumulate the same electro-optical characteristics. The simulation results show that the display exhibits reasonably low operating voltage, high optical efficiency and well-matched voltage-dependent transmittance (VT) and reflectance (VR) curves. Besides, the driving mode and the fabrication process of the transflective liquid crystal display are fairly simple and it is suitable for mobile applications.     

Transflective blue-phase liquid crystal display with dielectric protrusion

A transflective blue-phase liquid crystal display (TRBP-LCD) with dielectric protrusions is proposed. The dielectric protrusions are fixed on the in-plane-switching (IPS) electrodes. The potential drops very slowly in the dielectric protrusions, thus the total field penetrating depth is significantly enlarged and the operating voltage is lowered, which helps suppressing electrostriction effect. The different heights of the dielectric protrusions in the transmissive (T) and reflective (R) regions contribute to balance the optical phase retardation between the T and R regions. The simulation results verify that the proposed TRBP-LCD can achieve low operating voltage and good sunlight readability.     

The effect of terminal chain modifications on the mesomorphic properties of 4,4′-disubstituted diphenyldiacetylenes

The typical sidewalls produced in the fabrication of protrusion electrodes are proposed to create a low voltage (4.5 V_rms) and high transmittance (93%) blue-phase liquid crystal display (BP-LCD). The tilted electrodes produce a strong horizontal electrical field that reduces the operating voltage considerably. The common problem of the ‘dead zones’ is solved by reflecting the light onto the electrodes. In order to estimate the phase retardation of the reflected light, a ray tracing simulation program for anisotropic mediums has been developed. The proposed device is more competitive than vertical field switching based BP-LCD and also, has the advantages of protruded in-plane-switching structures. These facts make this technology a potential candidate for the next generation of BP-LCDs.     

Low voltage and high transmittance transflective blue-phase liquid crystal display with opposite polar electrodes

A single-cell-gap transflective polymer-stabilised blue-phase liquid crystal display with opposite polar pixel electrodes on an etched substrate is proposed. In the proposed structure, the space between common electrodes is adopted as transmissive region, and the space above the common electrode is adopted as reflective region. By optimising the electrode parameters of the transmissive and reflective regions, well-matched voltage-dependent transmittance and reflectance curves can be obtained. In addition, the device has good performances of low operating voltage (~3.2 V), high optical efficiency and a wide viewing angle.     

Blue-phase liquid crystal display with insulating protrusion

In order to lower the saturation voltage and enhance the transmittance of in-plane switching blue-phase liquid crystal display (IPS-BPLCD), IPS-BPLCD with insulating protrusion is proposed. The single-protrusion (only set on the top of pixel electrode) and double-protrusion (set on the top of pixel and common electrodes) structures are investigated in this work. The potential distribution changes when the protrusion is used. There is a thicker transverse electric field in BPLC range, because the stronger electric field at the edges of the electrodes is decentralised into BPLC range. As a result, the saturation voltage is reduced from 36.3 V to 28.9 V when the double-protrusion structure is used, and transmittance is increased by ~20%. The contrast ratio is larger than 1000:1 in 60° viewing cone using a half-wave biaxial film. Both single-protrusion and double-protrusion structures have the uniform gamma curves at large oblique viewing angles. Moreover, the off-axis image distortion index is 0.1590 at 60º polar angle when zigzag electrodes are used.     

Low-voltage and high-transmittance blue-phase liquid crystal display with concave electrode

A low-voltage and high-transmittance blue-phase liquid crystal display (BPLCD) with concave electrodes is proposed. We use in-plane switching electrodes on the etched substrates to generate the concave electrodes. The proposed device can generate a strong in-plane field with a large horizontal component to increase the transmittance and reduce the operating voltage. As a result, a low voltage ~9 V and reasonably high transmittance ~71.7% can be achieved. Moreover, due to the generated multi-domain structures in the etched areas, this BPLCD can obtain a symmetric and wide viewing angle and the contrast ratio of 1000:1 is obtained over 60° viewing cone.     

Effects of rubbing angle on maximum transmittance of in-plane switching liquid crystal display

Measurements of the maximum transmittance of an in-plane switching liquid crystal display showed that it increases as rubbing angle is increased from 10 to 20°. This dependence was analysed in terms of the local variation of electric field intensity between electrodes, which in turn makes liquid crystal at various positions between the electrodes rotate to different angles. The local variation of electric field becomes prominent, especially in the case that the distance between the electrodes is much larger than the cell gap or electrode width.     

High-transmittance polymer-stabilised blue-phase liquid crystal display with double-sided protrusion electrodes

A polymer-stabilised blue-phase liquid crystal display (PSBP-LCD) with double-sided protrusion (DSP) electrodes structure is proposed. The oblique electric field between the protrusion electrodes inside both top and bottom glass substrates can induce more isotropic-to-anisotropic transition in the polymer-stabilised blue-phase liquid crystal (PS-BPLC) medium through Kerr effect than using the in-plane switching electrode. For the same electrode width, spacing and cell gap, the transmittance of PSBP-LCD with the DSP electrodes is ～29% higher than that using the IPS electrode.     

Reflective blue phase liquid crystal displays with double-side concave-curved electrodes

Reflective blue phase liquid crystal display (BPLCD) is a promising candidate for field sequential colour displays with reflective liquid-crystal-on-silicon (LCoS). However, the issue of high operation voltage still hinders its widespread applications. We propose a reflective BPLCD with double-side concave-curved electrode and research its operation voltage and electro-optic characteristics in simulation, which is compared to the transmissive mode. The effect of double-side electrodes on horizontal electric field and operation voltage is analysed. The improvement of concave-curved electrodes on reflectance is discussed. A reflective BPLCD has two times the optical path difference compared to the transmissive mode. By using double-side concave-curved electrodes, the reflectance increased by 23% and the operation voltage reduced by 32% compared to the traditional in-plane switching mode. This work enables BPLC to be integrated with reflective LCoS.     

Continuous hydrophoretic separation and sizing of microparticles using slanted obstacles in a microchannel

We report a microfluidic separation and sizing method of microparticles with hydrophoresis--the movement of suspended particles under the influence of a microstructure-induced pressure field. By exploiting slanted obstacles in a microchannel, we can generate a lateral pressure gradient so that microparticles can be deflected and arranged along the lateral flows induced by the gradient. Using such movements of particles, we completely separated polystyrene microbeads with 9 and 12 microm diameters. Also, we discriminated polystyrene microbeads with diameter differences of approximately 7.3%. Additionally, we measured the diameter of 10.4 microm beads with high coefficient of variation and compared the result with a conventional laser diffraction method. The slanted obstacle as a microfluidic control element in a microchannel is analogous to the electric, magnetic, optical, or acoustic counterparts in that their function is to generate a field gradient. Since our method is based on intrinsic pressure fields, we could eliminate the need for external potential fields to induce the movement of particles. Therefore, our hydrophoretic method will offer a new opportunity for power-free and biocompatible particle control within integrated microfluidic devices.     

Cell gap‐dependent transmission characteristics of a fringe‐electric field‐driven homogeneously aligned liquid crystal cell,for a liquid crystal with negative dielectric anisotropy

Transmittance characteristics were studied as a function of cell gap for a homogeneously aligned liquid crystal (LC) cell driven by a fringe‐electric field—named fringe‐field switching (FFS) mode. The light efficiency of a conventional LC cell using in‐plane switching and twisted nematic modes, where the LC director is determined by competition between elastic energy and electrical energy, does not depend on cell gap as long as the cell retardation value remains the same; i.e. only dielectric torque contributes to the deformation of the LC director. However, the transmittance of the FFS mode is dependent on the cell gap such that it decreases as the cell gap decreases, although the cell retardation value remains the same. This unusual behaviour (unlike that of conventional LC cells) arises because in the device the elastic and dielectric torques have the role of determining the LC director, such that the driving voltage giving rise to maximum transmittance becomes strongly dependent on the electrode position when the cell gap is as small as 2?µm. In addition, the LCs at the centre of the pixel and common electrodes are not sufficiently twisted because of a competition between the two elastic forces, which tries to twist the LCs in plane and hold them in their initial state by surface anchoring.     

Image analysis method to study electro-optic parameters of nematogens

This paper demonstrated the image analysis technique for the investigation of electro-optic behaviour of homogeneously aligned nematic liquid crystals p-n alkyl benzoic acids (nBA) where n = 5 and 6 under the application of direct current (DC) electric field. Textures of the liquid crystals in the mesophase region of particular temperature were recorded in three monochromatic image planes at the wavelengths of 635 (red), 530 (green) and 475 nm (blue) as a function of applied DC voltage. Electro-optic properties such as transmittance, birefringence, phase retardation and contrast ratio were measured by analysing the optical intensities of the recorded textures using MATLAB software. The changes in the textural features and formation of new textures as a function of voltage provided information for better understanding of the electro-optic characteristics of liquid crystals. Results of this study were compared with the data of the other standard techniques: laser source (633 nm) experiment and United Detector Technology (UDT) sensor of model UV- 35P silicon photo diode which uses white light as source and filters the wavelengths using three colour filters of wavelengths 635, 530 and 475nm.     

Manipulating particles in microfluidics by floating electrodes

Various particle manipulations including enrichment, movement, trapping, separation, and focusing by floating electrodes attached to the bottom wall of a straight microchannel under an imposed DC electric field have been experimentally demonstrated. In contrast to a dielectric microchannel possessing a nearly uniform surface charge (or ζ potential), the metal strip (floating electrode) is polarized under the imposed electric field, resulting in a nonuniform distribution of the induced surface charge with a zero net surface charge along the floating electrode's surface, and accordingly induced-charge electroosmotic flow near the metal strip. The induced induced-charge electroosmotic flow can be regulated by controlling the strength of the imposed electric field and affects both the hydrodynamic field and the particle's motion. By using a single floating electrode, charged particles could be locally concentrated in a section of the channel or in an end-reservoir and move toward either the anode or the cathode by controlling the strength of the imposed electric field. By using double floating electrodes, negatively charged particles could be concentrated between the floating electrodes, subsequently squeezed to a stream flowing in the center region of the microchannel toward the cathodic reservoir, which can be used to focus particles.     

Movement of colloidal particles in two-dimensional electric fields

We characterize the movement of carbon black particles in inhomogeneous, two-dimensional dc electric fields. Motivated by display applications, the particles are suspended in a nonpolar solvent doped with a charge control agent. The two-dimensional fields are generated between strip electrodes on a glass slide spaced 120 microm apart with field strengths up to 10(4) V/m. Such fields are insufficient to drive either electrohydrodynamic instabilities or natural convection due to ohmic heating, but they move the particles between the electrodes in about 30 s. In the center region between the strip electrodes, the particles move by electrophoresis; that is, the particle velocity is proportional to the electric field. However, when imposing a constant-potential or constant-current boundary condition at the electrodes to derive the electrical field, the electrophoretic mobility calculated from the measured particle velocities is outside the range of mobilities predicted from the theory of O'Brien and White. Near the electrodes the particles either speed up or slow down, depending on the polarity of the electrode, and these changes in velocity cannot be explained simply by electrophoresis in a spatially varying electric field. We suggest that this anomalous motion arises from electrohydrodynamic flows originating from the interaction between the space charge of the polarized layers above the electrodes and the electric field. Approximate calculations indicate such flows could be sufficiently strong to explain the anomalous trajectories near the edges of the electrodes.     

Electrochromism of amorphous WO<Subscript>3</Subscript> films under the conditions of proton deficiency

In the paper, the dynamics of electrical coloring of amorphous WO₃ films is studied in a planar system with aluminum electrodes. Photography and computer processing of images is used. Several types of heterogeneities are found in the distribution of the coloring centers: longitudinal and transverse failures in the colored phase (cracks), saw-tooth optical density waves. To explain these phenomena, a model was suggested based on the assumption that circulation of electric current appears in the regions with a highly heterogeneous coloring and the hence generated magnetic field stabilizes these heterogeneities.     

Electrically developed morphology of carbon nanoparticles in suspensions monitored by in situ optical observations under sinusoidal electric field

In situ optical observations were performed for suspensions composed of carbon nanoparticles under the sinusoidal electric field with an amplitude around 20 kV/mm (volt per micrometer) and various frequencies. For extremely diluted suspensions of mixed fullerenes or multiwalled carbon nanotubes (MWNTs) in a silicone oil, the dark-field optical microscopy was effective for the in situ observation of the particle behavior under the electric field. The nanoparticles in a fullerene suspension under the sinusoidal electric field with a frequency of 100 Hz (in short, 100 Hz electric field) were aggregated to form a rigid spherical microstructure around the halfway between the electrodes. On the other hand, the nanoparticles in an MWNT suspension under 100 Hz electric field were also aggregated but aligned to form a chain-like microstructure which spans the electrodes. Both of the aggregated particles were stable even after the removal of the electric field, and they were redispersed by application of 10 Hz electric field.     

Dielectric relaxation studies and electro‐optical measurements in poly(triethylene glycol dimethacrylate)/nematic E7 composites exhibiting an anchoring breaking transition

Electric field driven anchoring breakage in poly(triethylene glycol dimethacrylate)/nematic E7 composites was studied using dielectric spectroscopy and transmittance measurements. The transmittance hysteresis observed on increasing and decreasing an applied electric field, associated with different alignment states of the liquid crystal (LC), was monitored through dielectric loss. Essential changes are felt mainly in the δ‐peak, i.e. the dielectric response of the nematic when the director lies parallel to the applied electric field. An irreversible effect persists after the field had exceeded a critical value, which was manifest in a higher transmittance and a higher dielectric strength of the δ‐peak in the OFF state. The initial scattering/opaque state of the sample can only be recovered by heating to the clearing temperature of the nematic LC. The effect referred, commonly called memory effect, is rationalized in terms of anchoring breakage of the LC at the polymer–LC interfaces. The electro‐optical response was tested for different poly(triethylene glycol dimethacrylate)/nematic E7 composites in different composition ratios prepared by polymerisation‐induced phase separation. The lowest threshold field was observed for the 30:70 composite.