Pretilt Angle Research Articles

27‐1: Study on the effect of controlling the pretitle angle using RM with multipolymerizable functional group

RM have played an integral role in the produce of generating the pretilt angle. In this study,we use Reactive Mesogen with multipolymerizable functional group and adopt UV curing process to investigate the pretilt alignment of liquid crystal ,and normal RM (RM with two polymerizable functional group) as a reference. The pretilt angle formation and reliability performance of different RM are discussed.

P‐205: Late‐News Poster: LED Induced Vertical Alignment Surface for High Performance Liquid Crystal Displays

Photoalignment is one of the best candidates of the proven market for multi domain display. It allows nearly free pattern to the liquid crystal alignment direction compared to the conventional rubbed polyimide. Most of the available photoalignment materials require polarized deep UV irradiation with a finite dosage. With the consideration of the current limitation with such a small working window, a vertical photoalignment surface by non‐polarized LED light irradiation with large wavelength is proposed and demonstrated. The alignment direction of proposed surface is generated by the inclined non‐polarized light. The measurement results show the alignment properties of this proposed alignment surface are comparable to conventional polyimide. It has stable and uniform pretilt angle, high polar anchoring energy and fast response time. As a result, the proposed alignment layer is robust and especially suitable for large‐area liquid crystal displays which require high performance with stable pretilt angles and multi‐domain purposes.

20‐1: Fast Switching Twisted‐Vertically Aligned Mode Reflective LCD using Mortar‐shaped Pixel Structure

We have developed fast switching twisted‐vertically aligned mode reflective LCD using mortar‐shaped pixel structure. We realized axially symmetric pretilt angle in each pixel by the mortar‐shaped pixel structure fabricated by the UV pattern exposure and achieved high quality reflective LCD with high reflectivity and wide viewing angle range.

Electro-optical and dielectric properties of TiO2 nanoparticles in nematic liquid crystals with high dielectric anisotropy

The electrical, optical and dielectric performance of high-dielectric-constant TiO2 nanoparticles (NPs) dispersed in nematic liquid crystals (NLCs) with high dielectric anisotropy is demonstrated. TiO2 doping decreases the pretilt angle of the NLC cell because of the increase in Van der Waals interaction between the NLC molecule and alignment layer. Moreover, TiO2 doping strengthens the electric field in the NLC bulk and suppresses the ionic screen effect on the substrate surface, thus decreasing the threshold and driving voltages of the NLC cell. The measured field-off response time and estimated conductivity initially increase and then decrease with increased TiO2 concentrations. This phenomenon is due to the antagonism between the entrained ion impurities during fabrication and the ion harvest effect of TiO2 NPs. Dielectric spectral measurements reveal that TiO2 doping changes the relative permittivity and dielectric anisotropy of NLCs because of the changed space–charge polarisation and order parameters in the NLC bulk. The physical mechanisms are discussed in detail accordingly.

Dynamic control of polarization mismatch and coma aberrations in rod-GRIN assemblies.

We describe the use of stacked electrically tunable liquid crystal lenses (TLCLs), along with rod gradient index (GRIN) fixed focus lenses, for endoscopic applications. Architectural and driving conditions are found for the optimization of total aberrations of the assembly. Particular attention is devoted to the coma and polarization aberrations. The coma aberration is reduced by stacking two TLCLs with "opposed" pre-tilt angles (all molecules are in the same plane), and then two such doublets are used with cross oriented molecules (in perpendicular planes) to reduce the polarization dependence. The obtained adaptive rod-GRIN lens enables a focus scan over 80μm (with exceptionally low RMS aberrations ≤0.16μm), making possible the high-quality observation of neurons at various depths.

Ion-beam irradiation modified chemical and physical surface characteristics of polyethylene glycol film for liquid crystal aligning

ABSTRACTThe characteristics of ion beam (IB) irradiated polyethylene glycol (PEG) films were analyzed to determine their potential use as a liquid crystal (LC) alignment layer. The transmittance of the PEG films at various IB intensities was measured to verify the possibility of using it as an alignment layer. Anti-parallel cells with the PEG film were fabricated to examine the LC alignment characteristics. Perfectly dark cross-polarized microscopy images were obtained at an intensity of 700 eV, which indicates uniform LC alignment, and pre-tilt angle measurements supported this finding. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) analyses were conducted to determine the effect of the IB irradiation on the PEG film on the surface modification. After exposure at an IB intensity of 700 eV where uniform LC alignment was achieved, remarkable chemical composition modification of the PEG film, including the reduction of C-O bonds that affected the uniform LC alignment, was observed via the XPS analysis. Furthermore, the AFM analysis revealed that low kurtosis value was obtained at this IB intensity. Therefore, we are convinced that the PEG films irradiated at this low IB intensity show potential as alternative alignment layer in LC applications.

Physicochemical analysis of ion beam-induced surface modifications on polyethylene glycol films for liquid crystal alignment

ABSTRACTWe investigated the surface modification induced by the ion-beam (IB) irradiation of a polyethylene glycol (PEG) film and its liquid crystal (LC) alignment characteristics. The X-ray photoelectron spectroscopy analysis revealed the chemical modification; as the IB incidence angle increased, the number of surface C–O bonds decreased, inducing an anisotropic dipole moment on the PEG film surface. In addition, the physical modification was demonstrated via atomic force microscopy analysis using three-dimensional images as a function of the IB incidence angle. The surface roughness was analyzed; the modification with the smoothest surface was observed for an IB incidence angle of 45°. This modification affected the LC alignment state of the PEG film, as demonstrated by the polarized optical microscopy analysis with pre-tilt angle measurements. Furthermore, for the same IB incidence angle, the residual DC measured using the capacitance–voltage curves was extremely low. Hence, a PEG film irradiated with an IB incidence angle of 45° could be a suitable LC alignment layer.

Curvature-induced structural transition of nematic liquid crystals in coaxial cylinder [formula omitted] cell: From bulk to surface order reconstruction

The structural transition of asymmetric π cell under a certain voltage was investigated to understand the display mode and performance of flexible substrates. Nematic liquid crystals show a splay texture at ground state (off state) and bend texture at on state induced by electric field in planar π and coaxial cylinder π cells. Changes in the topological discontinuous transformation of liquid crystal directors can appear between on and off states, and the symmetric splay state can be directly transited to the bend state by order reconstruction under high voltage. This phenomenon cannot be explained by Frank theory. Thus, we used Landau–de Gennes theory to study the effects of curvature on order reconstruction and the splay–bend transition through the detailed process of time dynamics. Results show that bulk-order reconstruction appears in planar π cell, whereas surface-order reconstruction appears in coaxial cylinder π cell because of the existence of a finite curvature radius. Moreover, the results will not change when we exchange the inner and outer boundary conditions under coaxial cylinder π cell. By changing the setting of pretilt angle and comparing the results in planar π and coaxial cylinder π cells, we found that the position of order reconstruction is close to the boundary when the curvature is large.

High-Transmittance 2π Electrically Tunable Terahertz Phase Shifter with CMOS-Compatible Driving Voltage Enabled by Liquid Crystals

We have investigated tunable terahertz (THz) phase shifters that are based on a sandwiched liquid crystal (LC) cell with indium–tin–oxide (ITO) nanowhiskers (NWhs) as transparent electrodes. More than 360° of phase shift at 1.0 THz was achieved at a driving voltage as low as ~2.6 V (rms). This is approximately 40 times smaller than that reported in previous works using an electrically tuned LC device. Significance of the NWhs in reducing the required voltage is demonstrated. Overall transmittance of the device is as high as 30%, which is accountable by absorption losses of ITO NWhs, quartz substrate and LC. Experimental results are in good agreement with a theoretical formulism while taking into account super-thick LC cells (~1 mm) and pretilt angles. We also propose and demonstrate a novel THz technique for measuring pretilt angles of liquid crystals.

The Effect of Ion-Beam Bombardment on Solution-Processed Nickel Oxide Films Used for Liquid Crystal Alignment

We induced a homogeneous liquid crystal (LC) alignment state on ion-beam (IB)-irradiated NiO films fabricated via solution-processing. A topographical analysis was performed using field emission-scanning electron microscopy of the films after various annealing temperatures. After IB irradiation, the surface of the NiO films was rough irrespective of annealing temperature. IB-irradiated NiO films exhibited slightly reduced transparency in the visible region compared to as-deposited NiO film. Moreover, the IB-irradiated NiO films fabricated at the lowest annealing temperature of 100°C exhibited uniform homogeneous LC alignment caused by microgroove-like topographic modification and chemical modification of the NiO surface by the IB irradiation. The pretilt angle of the LC molecules on IB-irradiated NiO film annealed at 100, 200, 300, and 400°C were on average 0.02 0.05, 0.43, and 0.05o, respectively, making IB-irradiated NiO film eminently suitable for LC alignment.

Liquid-Crystal-on-Silicon for Augmented Reality Displays

In this paper, we review liquid-crystal-on-silicon (LCoS) technology and focus on its new application in emerging augmented reality (AR) displays. In the first part, the LCoS working principles of three commonly adopted LC modes—vertical alignment and twist nematic for amplitude modulation, and homogeneous alignment for phase modulation—are introduced and their pros and cons evaluated. In the second part, the fringing field effect is analyzed, and a novel pretilt angle patterning method for suppressing the effect is presented. Moreover, we illustrate how to integrate the LCoS panel in an AR display system. Both currently available intensity modulators and under-developing holographic displays are covered, with special emphases on achieving high image quality, such as a fast response time and high-resolution. The rapidly increasing application of LCoS in AR head-mounted displays and head-up displays is foreseeable.

Liquid crystal alignment properties on surface-reformed solution-derived lanthanum-doped zinc oxide films

ABSTRACTLiquid crystal (LC) alignment characteristics were investigated using a solution-derived lanthanum-doped zinc oxide (La:ZnO) film that was exposed to various intensities of ion-beam (IB) irradiation. At an IB intensity of 1700 eV, uniform and homogeneous LC alignment was achieved, as revealed by cross-polarized optical microscopy and pre-tilt angle measurement. Field-emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) were used to verify that the IB irradiation induced physical and chemical surface reformation of the La:ZnO film that relate to LC alignment. FE-SEM and AFM revealed that the IB irradiation reformed the existing surface structure into a new structure with an altered surface roughness. The XPS results showed that the van der Waals force with anchoring energy increased as the IB intensity increased, and this profoundly affected the state of LC alignment. The capacitance-voltage (C-V) hysteresis curve was measured as a function of IB intensity to characterize the accumulated charge as a residual DC. Nearly zero C-V hysteresis was achieved at an IB intensity of 1700 eV. Therefore, a solution-derived La:ZnO film with an IB intensity of 1700 eV has great potential for high-quality LC applications.

Magnetic Freedericksz transition in a ferronematic liquid crystal doped with spindle magnetic particles

In this work we studied new composite ferronematic system based on the liquid crystal 4-n-hexyl-4′-cyanobiphenyl (6CB) doped with hematite spindle-like magnetic particles. We experimentally showed that magnetic moments of the elongated spindle particles are oriented perpendicularly to their main axes. It is a fundamental difference of our systems from ferronematics, which were synthesized before by many authors. For a research of magnetic and orientational properties of new composite materials, the ferronematic samples were prepared with different length of the particles and with the volume concentrations of solid impurity ϕ1=10−3, ϕ2=10−4 and ϕ3=10−5. The structural Freedericksz transition in ferronematic samples were observed by capacitance measurements in a capacitor made of ITO-coated glass electrodes. Experimental results showed a decrease of the critical field in the ferronematic samples in comparison with the pure 6CB, and an increase of the threshold shift with a growth of both the volume fraction of solid impurity and the length of particles. The response of capacitance to low external magnetic field - far below the magnetic Freedericksz transition threshold of prepared samples was also observed experimentally. For a theoretical description of this magnetically induced behavior of composite systems, the continual model of ferronematics with bistable coupling between colloidal particles and the nematic matrix was used. This theory permits the equilibrium tilted orientation of the particles with respect to the nematic director. We showed that it creates a so-called “pretilt angle effect” which explains the behavior of the ferronematic systems in a low field regime as well as decrease of the threshold field and the dependence of this field on the volume fraction of solid impurity and the length of the particles.

Influence of Pre-Tilt Angles of Liquid Crystalline Molecules Placed Onto Orienting Substrates on Characteristics of Liquid Crystalline Modulators Based on π-Cells

Influence of Pre-Tilt Angles of Liquid Crystalline Molecules Placed Onto Orienting Substrates on Characteristics of Liquid Crystalline Modulators Based on π-Cells

New Photo-Crosslinkable Benzaldehyde Polymers for Creating Liquid Crystal Lenses

We have studied new photo-crosslinkable benzaldehyde polymers with fragments including long hydrocarbon substituents in a side chain, as materials for creating a specified distribution of the pretilt angle of the director in a liquid crystal cell. We show that by changing the UV radiation exposure dose after rubbing the polymer layers, we can specify any pretilt angle in the range 0–90o. We have obtained the distribution of pretilt angles needed for creating liquid crystal lenses, where the maximum azimuthal anchoring energy of the liquid crystal with the alignment layer is increased to 2.5·10–5 J/m2, which allowed us to substantially reduce the number of defects and to improve the optical quality of the liquid crystal lens.

The polar anchoring energy of nematic liquid crystals with polyvinylidene fluoride alignment layer

ABSTRACTIt has been proved that the high dielectric polyvinylidene fluoride (PVDF) could be used as an alignment layer in liquid crystal device. In this paper, the transmittance, pretilt angle and the polar anchoring energy of the substrates with PVDF alignment layer were researched. Theoretical results and the experimental results about the reflectivity RSS (polarisation-conserving signals) recorded by full-leaky guided mode in liquid crystal technique are analysed to evaluate the anchoring energy of PVDF alignment layer. The result shows that the polar anchoring energy between PVDF alignment layer and liquid crystal molecules is 2.80 × 10−4 J/m2.

Conjugation of Nanomaterials and Nematic Liquid Crystals for Futuristic Applications and Biosensors.

The established role of nematic liquid crystals (NLCs) in the recent rapid development of displays has motivated researchers to modulate the electro-optical properties of LCs. Furthermore, adding nanomaterials into NLCs has led to enhancements of the properties of NLCs, like reduced threshold of the operating voltage, variation in pretilt angle, reduced switching time, etc. These enhanced properties, due to interfacial dynamics, are enabling wider applications of NLCs and nanomaterials. The recent literature of nanomaterial-doped NLCs is rich with various kinds of nanomaterials in a variety of NLCs. The light has been focused on the most widely used and studied gold nanoparticles in NLCs. The intrinsic inherent property of easy excitation of surface plasmons polaritons (SPP) is the mediating interaction of NLC electric dipoles and the polarization of charges in the GNP surface. The concepts and methods for the application of metal nanomaterials as dopants in NLCs are discussed for future applications, especially biosensors. The biosensing application of NLCs alone has already been proven in the literature. However, it is always desirable to further enhance the detection efficiency and selectivity, which have been achieved by the conjugation of GNPs and nickel nanoparticles with NLCs and their compatibility with biological materials. This aspect of future application of nanoparticles and NLC makes the point more selective to be included in the present manuscript.

Optics of light scattering caused by liquid-crystal-director fluctuations

ABSTRACTWe have applied the light-scattering equation caused by liquid-crystal (LC)-director fluctuations as derived by De Gennes [1] to the case where the polarization direction of the incident light is at an arbitrary angle with respect to the LC directors within the cell. Based on the De Gennes’s equation, we have used an out-of-plane (OPR) cell-rotation method to measure the pretilt angles of a tilted-homogeneously aligned LC cell. Our measured pretilt angles are in good agreement with that obtained by the published OPR-rotation method [2] based on a different mechanism. Our method is simple in setup and requires no complicated data-fitting calculations when the pretilt angles are below about 30°. In addition, there is no need to know cell parameters except the ordinary and extraordinary refractive indices of the LC medium at the wavelength of incident light.

Growth of ZnO Nanorods and Their Applications for Liquid Crystal Devices

Different morphologies of ZnO nanorods were synthesized by using the two-step hydrothermal method, and they were applied to liquid crystal (LC) alignment films. The morphology of the ZnO nanorods, including length, diameter, and density, were controlled by the growth time, which ranged from 16 to 26 min. The morphology and the chemical features both contributed to the surface wettability of the ZnO nanorods. The LC pretilt angle on the ZnO nanorods was successfully controlled from homeotropic (∼89.0°) to homogeneous (∼1.7°) alignments, as the contact angle of water on ZnO nanorods was changed from 93 to 28° with the growth time. The analysis of X-ray diffraction and X-ray photoelectron spectroscopy showed that the crystallite size of ZnO nanorods increased with the growth time, while the oxygen vacancy decreased. The ZnO nanorods grown on the ITO glass substrate also improve the transmission of LCDs due to the antireflection effect.

39.1: Invited Paper: Novel Photo-Alignment Material for Ultra-High Definition VA LCDs

Ultra-high definition vertically photo-aligned LC-displays inherently suffer from lower backlight transmittance. We proved, experimentally and by simulation, that the transmittance is increased by lowering the pre-tilt angle. Novel material based on Rolic's proprietary photo-alignment technology yielding low pre-tilt angles and high reliability is developed and qualified for mass production by CEC Panda.