Angle Of Liquid Crystal Molecules Research Articles

Mathematical modeling of inhomogeneous electric field impact on a liquid crystal layer

AbstractThe authors analyze the Fréedericksz transition phenomenon of reorientation of molecules in the plane liquid crystal layer in inhomogeneous electric field generated by parallel plate capacitor using the Oseen–Frank mathematical model. The capacitor is a set of short metal plates periodically located on both sides of the extended liquid crystal layer, connected in series in two circuits. When electric charges of different signs appear on opposite plates of the capacitor, the electric field in the periodicity cell turns out to be significantly inhomogeneous both in length and in thickness of the layer. Governing equations of the model represent Euler's variational equations in the problem on minimization of the potential energy of liquid crystal. Numerical solution of the equations uses the authorial variational difference scheme. The Laplace equation for electric potential in the exterior of the liquid crystal layer is solved using the method of lines. The electric field and the patterns of orientation angles of molecules inside the layer are determined by iterating with numerical solution of Poisson's equation using the fast Fourier transform at each iteration step. The algorithm is implemented by means of CUDA technology for computing systems with graphics accelerators. The scale of the mesh to ensure the computation accuracy is selected from calculation of Tsvetkov's order parameter in a rectangular cell pattern. Verification of the algorithm and program is implemented by way of comparing the computational results and the exact solution of the problem on the homogenous electric field with the constant initial orientation angle of liquid crystal molecules. The computations accomplished yield the patterns of the electric potentials and orientation angles of molecules depending on the position of the capacitor plates at uniform and s‐shaped initial distribution of the orientation angles through the thickness of the liquid crystal layer.

P‐108: Study of Trace Mura in ADS LCD

When the picture of L255 is pressed or slid, the cell gap is changed and the arrangement of liquid crystal molecules(LC) is disordered, resulting in the decrease of the brightness of the corresponding position, which cannot be recovered within the specified time (≤5s), it is called trace Mura. In this paper, the principle of trace Mura is introduced in detail, and a new simulation model is proposed. Using TechWiz software, the risk of trace Mura can be accurately simulated and quantified, and the simulation results are consistent with the actual phenomena. It is confirmed that the square angle of LC at the end of the electrode is changed suddenly (i.e. the opposite direction of the normal deflection direction of LC), and the mutation angle is −20°, which prone to trace Mura. In addition, four groups of influence factors (total 12 splits) are proposed for physical and simulation verification, and the optimized design scheme of pixel electrode is obtained. The following conclusions are obtained: the inner corner is cancelled, the length of the outer corner is ≥ 3um, and the angle of the outer corner on the right side (which has been referred to in Figure 4, and other pixel directions can be adjusted accordingly) is ≥ 45°, and the turning direction of the left side is in the same direction as the slit or at an acute angle with the slit direction; This scheme can reduce the dark area of the opening area and maximize the transmittance without risk of trace Mura.

Diffraction characteristics of a non-mechanical beam steering system with liquid crystal polarization gratings.

The non-mechanical beam steering system is composed of multiple liquid crystal polarization gratings (LCPGs) cascaded by binary or ternary technologies. However, cascading multiple LCPGs cause the beam from one LCPG to obliquely enter the subsequent LCPGs, changing their diffraction efficiency and working voltage at different steering angles. This paper uses the elastic continuum theory of liquid crystals to simulate the tilt angle of liquid crystal molecules under different voltages. The transmission process of the beam in the system at oblique incidence is described with an extended Jones matrix, and the highest diffraction efficiency and working voltage of each LCPG at different steering angles are calculated using vector diffraction theory. It is convenient to calibrate the LCPGs' working voltage and analyze the system's diffraction characteristics. In addition, we used an improved binary cascade technology to design a LCPG non-mechanical beam steering system with a steering angle of ±10° and an angular resolution of 0.67°. Compared with binary cascade, this technology can effectively reduce the number of cascaded devices and increase the system throughput under the same maximum beam steering angle and angular resolution.

Homogeneous liquid crystal alignment on poly(vinylidene fluoride-trifluoroethylene) films subjected to ion-beam irradiation

We demonstrate homogeneous and uniform liquid crystal (LC) alignment on poly(vinylidene fluoride-trifluoroethylene) [PVDF-TrFE] films using ion-beam (IB) irradiation and a performance improvement of twisted nematic (TN) cells using IB-irradiated PVDF-TrFE films. Spontaneous ferroelectricity of the PVDF-TrFE films was modified by IB irradiation, which affected the LC alignment properties. The variation in the pre-tilt angles of the LC molecules on the IB-irradiated PVDF films is attributed to surface reformation, including defluorination and oxidation because the pre-tilt angles of LC molecules can be controlled by adjusting the fluorine content. The results of contact angle measurements supported this phenomenon. A 58% reduction in the switching voltage was observed for TN cells, indicating that the IB-irradiated PVDF-TrFE films are a promising candidate for use as an alignment layer.

Investigation of Liquid Crystal Ripple Using Ericksen-Leslie Theory for Displays Subject to Tactile Force

Liquid crystal display panels subjected to tactile force will show ripple propagation on screens. Tactile forces change tilt angles of liquid crystal molecules and alter optical transmission so as to generate ripple on screens. Based on the Ericksen-Leslie theory, this study investigates ripple propagation by dealing with tilt angles of liquid crystal molecules. Tactile force effects are taken into account to derive the molecule equation of motion for liquid crystals. Analytical results show that viscosity, tactile force, the thickness of cell gap, and Leslie viscosity coefficient lead to tilt angle variation. Tilt angle variations of PAA liquid crystal molecules are sensitive to tactile force magnitudes, while those of 5CB and MBBA with larger viscosity are not. Analytical derivation is validated by numerical results.

Dependence of pretilt angle on orientation and conformation of side chain with different chemical structure in polyimide film surface

A series of polyimide films were synthesized based on various side-chained diamines, 4-phenylphenyl-3,5-diaminobenzoate (DABB), 6-(4-phenylphenoxy)hexyl-3,5-diaminobenzoate (C6BB), 6-(4-(4-butoxylphenyl)phenoxy)hexyl-3,5-diaminobenzoate (C6BBC4) and 4-(4-butoxylphenyl-phenyl-3,5-diaminobenzoate (BBC4), the side chains of which contain a rigid biphenyl linked with flexible alkyl. The pretilt angle of liquid crystal molecules on the side-chained polyimide films based on C6BBC4 or BBC4 (PI-C6BBC4 or PI-BBC4) increased obviously with increasing side chain content and even achieved 87–89°. In contrast, the polyimide film based on C6BB or BB (PI-C6BB or PI-BB) even with a high side chain content could only achieve the homogeneous alignment. The properties and microscopic structure of the functionalized polyimide films were analyzed by polarized ATR-FTIR, computer simulations and surface energy etc. It was found that the side chains with different chemical structure get the different orientation and conformation in the outmost layer of polymer film, affecting the pretilt angle of liquid crystal molecules on this film surface. For PI-BBC4 and PI-C6BBC4, the side chains with the non-polar group at the tail take the vertical conformation in the outer layer of the polymer surface, which benefited the liquid crystal to get a large pretilt angle, even vertical alignment on the film surface. The side chain of PI-C6BB with the flexible alkyl spacer is equipped with good mobility. It is easy for its polar mesogen groups at the surface to take the conformation parallel to the polymer film, which leads to the formation of homogeneous alignment of LC molecules.

Mueller–Stokes polarimetric characterization of transmissive liquid crystal spatial light modulator

In the twisted nematic liquid crystal spatial light modulators (TN-LCSLM), distortion of uniform twist and decrease in tilt angle of liquid crystal molecules on application of an electric field lead to amplitude and phase modulations of the transmitted or reflected wavefront, respectively. The amplitude and phase modulation characterization of TN-LCSLM using Jones calculi is simple and extensively used but does not give any information about important polarimetric parameters such as diattenuation and depolarizance. On the other hand, the characterization using Mueller calculi provides all information in terms of polarimetric properties such as diattenuation, retardance (birefringence) and depolarization. In this paper, polarimetric properties of the transmissive TN-LCSLM (HOLOEYE LC2002) are characterized measuring 17 different Mueller matrices at different addressed gray scale through Mueller Matrix Imaging Polarimeter (MMIP) at 530 nm wavelength. Lu–Chipman polar decomposition for Mueller matrix is utilized to separate out three independent Mueller matrices for diattenuation, depolarization and retardance as a function of addressed gray scale. Further, Mueller–Stokes combined formulation is used to examine the effect of depolarization present in the TN-LCSLM on six different states of polarization and evaluation of eigenpolarization states for the TN-LCSLM has been presented.

Effect of the skeleton structures in the side chain of polyimides on their film surface properties and pretilt angles of liquid crystal molecules

Polyimides (1c–4c, 1c'–4c') with side chains (1–4) containing four different skeletons were synthesised and characterised. Results showed that a similar high side chain abundance took place on the surface of the films, which was independent of the skeleton structures, while the pretilt angles of liquid crystal molecules were considerably affected by the skeleton structures. 1c, 1c' and 2c, 2c' achieved vertical alignment while 3c, 3c' and 4c, 4c' only obtained low pretilt angles. The main reason, based on surface testing results and molecular modelling, was the different interactions between liquid crystal molecules and the skeletons in the side chains.

Nanoparticle-doped polyimide for controlling the pretilt angle of liquid crystals devices

The pretilt angles of liquid crystal molecules can be controlled by using conventional polyimide (PI) alignment material doped with different concentrations of Polyhedral Oligomeric Silsequioxanes (POSS) nanoparticles, which have been observed to spontaneously induce vertical alignment. The addition of POSS in the homogenous PI changes the surface energy of the alignment layer and generates a variable pretilt angle. Experimental results demonstrate that the pretilt angle thetap is a function of the POSS concentration, and can be tuned continuously over the range of 0 degrees <thetap<90 degrees. The polar anchoring energy of POSS/PI alignment layer is almost constant regardless of the POSS concentration. This technique is very simple and is compatible with methods familiar in the current LCD industry.

Effect of a biphenyl side chain of polyimide on the pretilt angle of liquid crystal molecules: molecular simulation and experimental studies

The side chain structure of polyimides (PIs) exerts an important effect on the pretilt angle of liquid crystal molecules. Three PIs with different side chain structures were prepared based on 3,3′,4,4′-biphenyl dianhydride (BPDA) and 1,3-phenylene diamine (m-PDA), 3,5-diaminobenzoic-4′-biphenyl ester (DABBE) and 4′-(tert-butyldimethylsiloxy) biphenyl-4-yl 3,5-diaminobenzoate (DPA). The surface properties of the PI films and the pretilt angles of the liquid crystal molecules on them were examined with experimental and molecular simulation methods, showing a good agreement between two methods. Molecular simulation showed that the BPDA-DPA system had the lowest surface energy for its side chain enriched on the PI surface, which was driven by the low polar silyl end group of side chain. The phenyl ring in the PI backbone tended to be arranged parallel with the surface, while the phenyl ring in the side chain inclined to align vertical to surface. By incorporation of the biphenyl group and the silyl end group, the pretilt angle of the PI increased from 3° to 89°. This was attributed to the enrichment degree of the side chain on the surface and the configuration of the biphenyl group in the side chain. The main interactions between the liquid crystal molecule, 4-n-pentyl-4′ -cyanobiphenyl (5CB) and the PIs was a π–π interaction between the biphenyl group in 5CB and the PIs.

Anisotropic Reflectivity of Rubbed Polyimide Liquid Crystal Alignment Layer

The surface optical anisotropy of rubbed polyimide films has been detected using reflection anisotropy spectroscopy. The amplitude of the reflection anisotropy signals increases with the rubbing strength. Rubbing also causes changes in pretilt angle of liquid crystal molecules which are in contact with the rubbed polyimide. An increase in rubbing strength results in an increase in the pretilt angel. The pretilt of the liquid crystal molecules was found to linearly correlate with the amplitude of the RA signals.

Long-Range Interactions between Nematicons

We theoretically and experimentally investigate the long-range interaction between nematicons. It is demonstrated that the interaction becomes strongest when the pretilt angle of liquid crystal molecules is nearly π/4 for a given single-beam input power P0, and that the interaction becomes stronger when the incident power P0 increases at a given pretilt angle. In this way, the interaction is still observed when the initial separation is 43 times of the soliton width, much larger than that implemented in lead glasses [Nature Phys. 2 (2006) 769].

Preparation of vertical alignment layers by blending polyimide precursors with and without side chains

A series of polyimides (PIs) were prepared from the precursors, blends of a poly(amic acid) and a side-chain poly(amic acid), based on a diamine 4′-(tert-butyldimethylsiloxy)biphenyl-4-yl 3,5-diaminobenzoate (DPA). The blended polyimide (bl-PI) films were relatively tough. The surface properties of the bl-PI films were characterised by surface energy measurement, X-ray photoelectron spectroscopy (XPS) and attenuated total reflectance infrared spectroscopy (ATR-IR). The results showed that the non-polar side chains were highly enriched on the surface and 90° pretilt angles of liquid crystal molecules were generated regardless of side chain content. For comparison, the copolyimides (co-PI) with different DPA contents were synthesised. It was found that the enrichment of the side chain on the surface increased with increasing DPA content and the pretilt angles of liquid crystal molecules rose from 3° to above 20° when DPA content increased from 10% to 30%. For the polyimides based on a diamine without a non-polar end group, 4′-biphenyl-4-yl 3,5-diaminobenzoate (DABBE), both bl-PIs and co-PIs could only generate the same low pretilt angles. In conclusion, by blending poly(amic acids) based on DPA, tough vertical alignment layers could be prepared.

3A11 アゾベンゼンを主鎖に含むポリイミドの光誘起傾斜配向と液晶のプレチルト角の関係(物理・物性)

3A11 アゾベンゼンを主鎖に含むポリイミドの光誘起傾斜配向と液晶のプレチルト角の関係(物理・物性)

Control of Pre-Tilt Angles of Liquid Crystal Molecules Using a Chemically Adsorbed Monomolecular Layer as an Alignment Film in Liquid Crystal Cells

Photoaligned monomolecular layers containing two materials were formed to control pre-tilt angles (θp) of liquid crystal molecules for twisted nematic (TN) type liquid crystal displays (LCDs) by a chemical adsorption (CA) technique and a photoalignment technique. One was a new chlorosilane type surfactant, 4′-(6-trichlorosilyloxyhexyloxy) chalcone (CO), having photopolymerizablity, and the other was a surfactant having a straight carbon chain (SC). Although we tried screening six different surfectants as an additive to CO, a surfactant having a long straight hydrocarbon chain (octadecyl-trichlorosilane: C18) was the most suitable for the TN type LCDs. By changing the molecular ratio of CO and C18, pre-tilt angles of liquid crystal molecules in a test liquid crystal (LC) cell could be controlled from 0 to 8° with perfect mono-domain alignment. When surfactants having short hydrocarbon chains and those having fluorocarbon chains were used, the quality of the TN type LC cells obtained was not good.

Syntheses and characteristics of polyimides for the applications to alignment film for liquid crystal display

AbstractIn this work, several polyimides (PIs) containing diphenyl ether group were synthesized and characterized by Fourier transform infrared spectroscopy and thermogravimetric analysis. The relationship between the surface structures and the molecular chain conformations of the PIs, whether helical or zigzag, was discussed. The effects of the molecular chain conformations of the PIs on the pretilt angles of liquid crystal molecules were systematically investigated. The surface orientations of polyimides whose chains adopt zigzag and planar conformations were less improved by rubbing treatment than those of polyimides whose chains adopt helical and nonplanar conformations, because the polyimide chains of zigzag and planar conformation are easily packed. The polyimides, whose chains adopt helical and nonpolar conformations, gave larger pretilt angles than the polyimides whose chains adopt zigzag and planar conformations. The pretilt angles measured under the condition of rubbing depth of 0.5 mm were smaller than under the condition of rubbing depth of 0.3 mm. © 2001 John Wiley &amp; Sons, Inc. J Appl Polym Sci 82: 2365–2371, 2001

An azo-isomerization-induced Freedericksz transition of a nematic liquid crystal

We observed an azo-isomerization-induced Freedericksz transition of the 5CB liquid crystal doped with 1% double-azo. In experiment, we found that the Freedericksz transition threshold occurred at optical intensity level of 0.3 mW/mm 2 for the 12.5 μm-thickness planar alignment doped 5CB, which is four orders of magnitude lower as that for the pure 5CB. Using optical phase retardation, we measured the relations between the Freedericksz transition threshold and the pump beam polarization. The maximum twist angle of liquid crystal molecules under different pump beam intensity is given. The experiment indicated that trans– cis isomerization plays an important role in the decrease of the Freedericksz transition threshold.

Liquid-crystal alignment on rubbed polyimide films with various side chains

A series of polyimides containing various side chains was synthesized in order to investigate the effect of side chains on the alignment of liquid crystals on the rubbed surface. Here, the side chains include short flexible alkyl spacers and isomeric biphenyl mesogens. The pretilting of liquid-crystal (LC) molecules was found to be very sensitive to the isomeric structure of biphenyl mesogen end groups as well as the conformation and length of flexible spacers, in addition to the rubbing process. The pretilt angle of LC molecules in the LC cell was achieved in a wide angle range of 8-27°, depending upon the rubbing density as well as the side chains. The high performance in the pretilt and alignment of LCs might be attributed mainly to a strong interaction between the biphenyl mesogen end group in the side chain and the LC molecule in addition to the microgrooves generated in the rubbing direction.

Evaluation of temperature and voltage dependences of nematic liquid crystal molecules on Langmuir–Blodgett films in the thick cell using the attenuated total reflection method

Tilt angles of nematic liquid crystal molecules, 5CB, have been investigated in the thick cells having aligning layers of polyimide (PI) Langmuir–Blodgett (LB) films on aluminum electrodes using the attenuated total reflection (ATR) measurement method. The ATR curves strongly depended upon AC voltages applied to the cells and the properties at each voltage were similar between 17 and 25°C. The resonant excitations of the surface plasmon polariton (SPP) were observed in a broad region of the incident angle in the ATR measurements. The tilt angles of the liquid crystal molecules were calculated by fitting the theoretical ATR curves to the experimental ones. The results showed that the ATR measurement method was very useful for evaluating behaviors of liquid crystal molecules in thick cells.

Evaluation of Tilt Angles of Nematic Liquid Crystal Molecules on Polyimide Langmuir-Blodgett Films using the Attenuated Total Reflection Measurement Method

The tilt angles of liquid crystal molecules, 5CB, have been investigated in liquid crystal cells with rubbing-free aligning layers of polyimide (PI) Langmuir-Blodgett (LB) films on aluminum electrodes using the attenuated total reflection (ATR) measurement method. The surface plasmon polariton (SPP) and/or the guided wave excitation modes (GWEM) were observed in the ATR curves of the liquid crystal cells when various DC voltages were applied to the cell. The ATR properties were evaluated from the SPP and the GWEM. The tilt angles of the liquid crystal molecules were calculated by fitting the theoretical ATR curves to the experimental ones using various models of the liquid crystal layer structure. Furthermore, the electric field intensities in the cell were calculated at several incident angles in the ATR curves. The ATR measurement is very useful for evaluating the alignment properties of liquid crystal molecules in liquid crystal cells.