A polarisation-independent blue-phase liquid crystal lens array using gradient electrodes

A polarisation-independent blue-phase liquid crystal lens array using gradient electrodes is proposed. A high dielectric constant layer helps to smoothen out the horizontal electric field and reduce the operating voltage. With gradient electrodes and a planar top electrode, gradient electric fields are generated and lens-like phase profile is obtained. When the applied voltage is changed, the focal length of the lens can be tuned from ∞ to 5.94 mm. Besides, the simulation results show that the lens is insensitive to polarisation while keeping parabolic-like profile.     

The in-plane switching of homogeneously aligned nematic liquid crystals

We have investigated the electro-optical effects and physical switching principle of homogeneously aligned nematic liquid crystals when applying an in-plane electric field with interdigital electrodes. By using the in-plane switching (IPS) of the liquid crystals which is achieved by the in-plane electric field, the viewing angle characteristics of the electro-optical effects were confirmed to be far superior to those of the conventional twisted nematic mode in which the electric field is applied along the direction perpendicular to the substrates. The non-reversal region of grey scales was extremely wide in which a high contrast ratio was kept, even along quite an oblique direction in the IPS mode. In order to clarify the switching principle of the liquid crystals in the IPS mode, a simplified expression describing the threshold behaviour of the device was derived with the assumption that a uniform in-plane electric field was applied along a direction perpendicular to the director and parallel to the homogeneously aligned nematic slab, and found to be sufficiently able to explain the experimental results. First, a critical field at which the liquid crystals just began to twist, was found to be proportional to the reciprocal of the cell gap. Second, it was the electric field and not the voltage that drives the liquid crystals. This relationship was due to the independence of the electric field regarding the liquid crystal layer normal direction. So the threshold voltage in the IPS mode was strongly dependent on the variation of the cell gap. For the dynamical response mechanism of the liquid crystals to the in-plane electric field, the switching on and off processes of the liquid crystals were analysed quantitatively. The relaxation time of the liquid crystals when removing the electric field could be described as proportional to the square of the cell gap. A thinner cell gap also proved to be effective in obtaining a fast response time in the IPS mode. In contrast, the switching on time when applying the in-plane electric field was found to be inversely proportional to the difference between the square of the electric field strength and the square of the critical electric field strength at which the liquid crystals began to deform.     

Effects of Applied Electric Fields on Drop—Interface and Drop—Drop Coalescence*

In this work, coalescence of a single organic or aqueous drop with its homophase at a horizontal liquid interface was investigated under applied electric fields. The coalescence time was found to decrease for aqueous drops as the applied voltage was increased, regardless of the polarity of the voltage. For organic drops, the coalescence time increased with increasing applied voltage of positive polarity and decreased with increasing applied voltage of negative polarity. Under an electric field, the coalescence time of aqueous drops decreases due to polarization of both the drop and the flat interface. The dependency of organic drop-interface coalescence on the polarity of the electric field may be a result of the negatively charged organic surface in the aqueous phase. Due to the formation of a double layer, organic drops are subjected to an electrostatic force under an electric field, which, depending on the field polarity, can be attractive or repulsive. Pair-drop coalescence of aqueous drops in the organic phase was also studied. Aqueous drop-drop coalescence is facilitated by polarization and drop deformation under applied electric fields. Without applied electric fields, drop deformation increases the drainage time of the liquid film between two approaching drops. Therefore, a decrease in the interfacial tension, which causes drop deformation, accelerates drop-drop coalescence under an electric field and inhibits drop coalescence in the absence of an electric field.     

A liquid crystal microlens obtained with a non-uniform electric field

Abstract

A homogeneously aligned nematic liquid crystal cell with a hole-patterned electrode and with an indium-tin oxide (ITO-) coated counter-electrode has been prepared. A non-uniform electric field can be produced by the asymmetrical electrode structure. The liquid crystal director can be reoriented by applying a voltage across the electrodes, and this produces an axially symmetrical profile of the refractive index. This liquid crystal cell is expected to have a lens effect and so its optical properties have been investigated. The profile of the output light intensity was measured by using a detecting system with an optical fibre. Some relationships between the lens properties, the diameter of the hole and the thickness of the liquid crystal layer have been examined. The liquid crystal cell becomes a convex (converging) lens with a relatively low voltage. A focal length of several millimetres can be obtained by applying voltages of 3-4 V. As the applied voltage increases, the focal length becomes longer, and the cell changes to a concave (diverging) lens when a high voltage is applied (? 20 V). These properties are discussed from the viewpoint of the director orientation effects resulting from the non-uniform electric fields in the cell.     

A liquid crystal microlens obtained with a non-uniform electric field

A homogeneously aligned nematic liquid crystal cell with a hole-patterned electrode and with an indium-tin oxide (ITO-) coated counter-electrode has been prepared. A non-uniform electric field can be produced by the asymmetrical electrode structure. The liquid crystal director can be reoriented by applying a voltage across the electrodes, and this produces an axially symmetrical profile of the refractive index. This liquid crystal cell is expected to have a lens effect and so its optical properties have been investigated. The profile of the output light intensity was measured by using a detecting system with an optical fibre. Some relationships between the lens properties, the diameter of the hole and the thickness of the liquid crystal layer have been examined. The liquid crystal cell becomes a convex (converging) lens with a relatively low voltage. A focal length of several millimetres can be obtained by applying voltages of 3-4 V. As the applied voltage increases, the focal length becomes longer, and the cell changes to a concave (diverging) lens when a high voltage is applied (≳ 20 V). These properties are discussed from the viewpoint of the director orientation effects resulting from the non-uniform electric fields in the cell.     

不同液体介质的高压静电雾化试验研究

自行设计、组装高压静电雾化试验装置,研究同一环境下煤油、乳化剂和酒精3种不同液体介质在高压静电场中的雾化过程.结果表明:液体介质的表面张力和粘性力越小、电导率越大,静电雾化效果越好.煤油、乳化剂和酒精分别在40 V,10 kV和25 kV时达到最佳的雾化效果.     

The optical response of liquid crystal cells to a low frequency driving voltage

This study investigates the optical response of liquid crystal cells to a low frequency square wave voltage of 0.1 Hz. It is found that there are three physical phenomena that dominate the overall properties of the device. The first is the discharging effect whereby the effective voltage over the liquid crystal layer decreases as a function of time; this occurs due to mobile ions being present within the liquid crystal material. The second is the charging-up of the cell where the effective voltage increases with time; this is attributed to charge separation taking place within the polyimide layer upon application of the d.c. voltage component. The third effect is cell asymmetry whereby the effective voltage depends upon the polarity of the externally applied field; this is the result of a locked-in d.c. holding voltage being present within the cell layers. These three effects are analysed in some detail with the view of developing a liquid crystal cell capable of being driven with a low frequency square wave voltage. A model of a liquid crystal cell in which the liquid crystal material can dissolve impurity ions from the alignment layers and in which the ions can then become re-adsorbed into the polyimide layer is deduced.     

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.     

Low-voltage blue-phase liquid crystal display with single-penetration electrodes

A blue-phase liquid crystal display (BPLCD) with single–penetration (S-P) electrodes is proposed to reduce the operating voltage. X-shape inclined-electric field is induced by the S-P electrodes with 2 ~ 3 μm height, which can lower the operating voltage by ~45%, and improve the transmittance compared with BPLCD with conventional in-plane electrodes. Moreover, the wide viewing angle and very small image distortion index can be obtained in this structure with a half-wave biaxial film. The proposed structure shows simple etching control and easy one-drop filling process of blue-phase liquid crystal compared with dual-convex-penetration electrodes.     

Polarisation-independent blue-phase liquid crystal microlens array with different dielectric layer

A fast response (sub-milliseconds) and polarisation-independent blue-phase liquid crystal (BPLC) microlens array with periodical double layer electrodes using different dielectric layers is proposed. The bottom double layer electrodes are coated with transparent and different dielectric layers to generate linearly varying electric potential from the centre to the edge, while the top planar electrode iridium tin oxide (ITO) electrode has a constant potential. As a result, gradient vertical electric fields are generated, and a gradient refractive index profile is obtained. When the applied voltage is changed, the focal length of the BPLC microlens array can be tuned from ∞ to 12.05 mm while keep a low operating voltage (~35V_rms). Besides, the driving mode (simplification driving) and fabrication process (using printing method or mold-pressing method) of the BPLC microlens array is very simple. The simulation results show that the BPLC microlens array is insensitive to the polarisation of incident light while keeping parabolic-like phase profile.     

Dynamics and rheology of immiscible polymer-liquid-crystal systems

The morphology evolution in immiscible polymer-liquid-crystal systems is quite different from flexible polymer-polymer mixtures due to the anisotropic properties of liquid crystals. The dynamics and rheology of such system are discussed. A theoretical model is proposed to describe the dynamics of liquid-crystal droplets in a flow field and the rheological properties of immiscible liquid-crystal/polymer mixtures. The deformation of liquid-crystal droplet is found to be greatly dependent on the interfacial properties of polymer-liquid crystal. The scaling relationships of interfacial contribution to the stresses are found to be quite different from the isotropic mixtures with droplet morphology.     

Macroscopic Networks of Carbon Nanotubes in PMMA Matrix Induced by AC Electric Field

It has been proven that electric fields can be used to improve the dispersion and alignment of carbon nanotubes (CNTs) in liquid media. In this article, an AC electric field is applied to blending of suspension of CNTs in methlmethacrylate (MMA) monomer during the polymerization of the MMA monomer initiated by 2 2‐azoisobytyronitrile (AIBN). Polymethlmethacrylate (PMMA) composites with macroscopic CNTs networks are prepared. It is found that morphologies of the CNTs networks are strongly dependent on the electric field parameters and polymerization conditions, such as the voltage, frequency, exerting time of the electric field, shapes of the electrodes for introducing the electric field, and the polymerization temperature. Increased voltage and frequency are found to be beneficial for the improvement of the CNTs dispersion and alignment, while fine CNTs networks are formed with optimized polymerization temperature and exerting time of the electric field.     

Polymer liquid crystalline composite for optical irradiation control

A composite material based on a liquid-crystalline gel has been prepared via the polymerization of diphenylolpropane dimethacrylate in the presence of the commercial nematic liquid crystal LC-1277 (94.3 wt %). Polymerization is performed under the action of UV irradiation. In the presence of the applied electric voltage, light scattering and birefringence of the samples are changed. The critical field of the electrooptical effect is found to be 2 V, the turn-on time of the effect is 9 ms (this time decreases with increasing voltage), and the turnoff time is 6 ms (independent of voltage). This material can be used in devices for optical irradiation control.     

Dependence of the anchoring energy on the applied voltage in a nematic cell

A nematic liquid crystal cell in the shape of a slab of thickness d and containing ionic impurities is considered in the presence of a dc voltage. A complete theoretical model to determine the electric field distribution across the sample is used to explain the experimental dependence of the effective anchoring energy of the cell on the applied voltage, in the limit of high voltage.     

Electrooptic properties of polymer dispersed liquid crystals

An investigation of the electrooptic properties of polymer dispersed liquid crystals (PDLC) is presented. These materials are light modulating systems. They show a reversible optical response from an opaque state to a highly transmitting state under the action of an appropriate electric field which aligns the liquid crystal director. The switching voltage required to establish such an electric field has been monitored as a function of (i) the starting materials used for the preparation of the PDLCs, (ii) the ageing (curing time) of the PDLC cells. Other physical properties, such as the electrical resistivity and the dielectric constant of the materials, have been measured. The correlations between these properties have been studied. The PDLC switching voltage appears to be strongly correlated with the resistivity. Our data suggest that ionic impurities play a dominant role with respect to the electrooptic response of PDLC films.     

Electrooptic properties of polymer dispersed liquid crystals

An investigation of the electrooptic properties of polymer dispersed liquid crystals (PDLC) is presented. These materials are light modulating systems. They show a reversible optical response from an opaque state to a highly transmitting state under the action of an appropriate electric field which aligns the liquid crystal director. The switching voltage required to establish such an electric field has been monitored as a function of (i) the starting materials used for the preparation of the PDLCs, (ii) the ageing (curing time) of the PDLC cells. Other physical properties, such as the electrical resistivity and the dielectric constant of the materials, have been measured. The correlations between these properties have been studied. The PDLC switching voltage appears to be strongly correlated with the resistivity. Our data suggest that ionic impurities play a dominant role with respect to the electrooptic response of PDLC films.     

The principle of parametric fractionation (separation) of substances in biological systems and technology

The parametric fractionation (separation) of substances is based on simultaneous exposure of a heterogeneous system with the phases (solid and liquid or liquid and gaseous) including components subject to be separated to the influence of two periodic fields of different nature. One field, “parameter” (for instance, temperature, pH) causes periodical redistribution of the components between phases, and the other field (for instance, mechanical forces, surface tension, electric field) effects synchronous shift of the components of one phase with respect to the other. As a result a counter flow of components to be separated formed against the gradient of their chemical or electrochemical potentials. This method underlain by the general principle of synchronous detection by no means is connected with definite mixtures or sorbents, it operates spontaneously in the inanimate and animate natural systems and can be applied to quite unexpected technologies.     

A guided wave study of the voltage dependent director configuration in a nematic liquid crystal layer with finite surface tilt

Prism coupling techniques have been used to excite optical modes in a thin nematic liquid crystal with finite surface tilt in order to study the voltage dependent director profile. The surface tilts are opposite in character and it is found that at zero applied volts the stable configuration is the substantially horizontal state. On applying the field this state is broken, probably transforming to the twisted vertical state. By modelling all the data obtained, the detailed behaviour of the director profile has been fully characterized yielding much information, including the change of surface tilt with applied voltage. For the nematic liquid crystal E7, this gives a voltage induced surface tilt of approximately 0.67° V^-1 for a 5.65 μm thick cell. Also using a boundary layer model, it has been possible to analyse the free energy in the cell and hence show that the observed twisted vertical state is the expected stable state under the field applied.     

Convective flow in the liquid crystal heat switch

The 'heat switch' is based on the fact that in some liquid crystal (LC) materials heat transfer depends on the voltage applied between two parallel electrodes containing the sample. The rate of heat transfer depends on the voltage rather than the electric field intensity, but is not understood. Since the heat switch can involve electric field intensities up to at least the breakdown field of air, it is important to understand the mechanism responsible for heat transfer. Results are presented indicating that a mechanism described earlier is involved. A proposal for a refrigerator using LC heat switches is also made.     

Optimal pixel design for low driving, single gamma curve and single cell-gap transflective fringe-field switching liquid crystal display

When a dielectric layer, in-cell retarder (ICR) is formed between the electrode and LC layer to obtain a single-gap transflective fringe-field switching (FFS) display, the driving voltage is highly increased due to the thickness of the dielectric material. In particular, the driving voltage of the transmissive part becomes very high, and goes beyond the driver integrated circuit (IC) range for mobile application because the homogenously aligned liquid crystal director should rotate twice as far as that in the reflective part. The correlation between the driving voltage and electrode structures was investigated. It was found that the problem could be solved by optimisation of the common electrode structure such that the electrode structure changed from a plane to slit shape (in-plane field is mainly used instead of fringe field), realising a high performance FFS transflective display.