For Ferroelectric Liquid Crystal Research Articles

P‐96: Alignment Optimization on Gen. 4.5 G for High‐framerate Ultra‐high‐resolution Ferroelectric Liquid Crystal Displays

We achieve high‐framerate (< 100 μs) high‐contrast‐ratio ferroelectric liquid crystal displays (FLCD) on Gen 4.5. Innovatively, a new polyimide (PI) that is suitable for ferroelectric liquid crystal (FLC) alignment is synthesized and tested on the production line. It replaces Nylon 6 (N6), which was the barrier to the commercialization of FLCD. Moreover, a new FLC is synthesized to match requirements in mass production. Additionally, various materials were studied to investigate the surface energy and relative performance. It is not only proof of the feasibility on the production line, but also a significant step towards the commercialization of field‐sequential‐color high‐resolution FLCDs.

Fluorinated Biphenylpyrimidine as a Possible Matrix for Ferroelectric Liquid Crystal Mixtures

The results of the synthesis and study of a new fluorinated achiral smectic C liquid crystal, namely, 2-(3-fluoro-4'-pentylbiphenyl-4-yl)-5-hexylpyrimidine, are presented. The possibility to use this compound as a matrix for ferroelectric liquid crystal (FLC) mixtures is evaluated. Two mixtures have been prepared: one (FLC-691-F) is based on new fluorinated compound and another (FLC-691) on its non-fluorinated analogue. The diester of optically active 2-octanol and terphenyldicarboxylic acid was used as a chiral dopant for both mixtures. Investigation of these FLC mixtures parameters: phase transition temperatures, helix pitch, spontaneous polarization and tilt angle show significant influence of fluorine atom. When comparing the phase sequence of FLC-691 and FLC-691-F mixtures, one can note that in the fluorine containing mixture an additional smectic A phase arises. At the same temperatures, the helix pitch of FLC-691-F is 2 – 2.5 times less than the helix pitch of FLC-691. The tilt angle of FLC-691-F is much smaller than that of FLC-691 but its value approaches the optimal value of 22.5 degrees, which ensures maximum light transmittance of electro-optical cells. At the same time the presence of fluorine atom in the matrix is a reason for the decrease of the mixture spontaneous polarization and a significant decrease (almost 4 times) in the driving voltage of electro-optical light shutters. As a result, it was shown that the fluorinated matrix provides new possibilities for controlling the mixture parameters.

Optimization of the dielectric and optical parameters of 1,2,4-oxadiazole ferroelectric mesophase with the suspension of PVP capped gold nanoparticles

In the present work, the dielectric and optical parameters have been optimized for ferroelectric liquid crystal (FLC), 1,2,4-Oxadiazole compound (C12*C10) when dispersed with PVP capped gold nanoparticles (GNPs). Dielectric (permittivity, loss) and optical-spectroscopic (UV–Visible absorbance, FTIR, and photoluminescence spectra) properties have been investigated to probe into the effect of the electromagnetic field on pure and GNPs dispersed FLC matrix. Polarizing optical textures of GNPs dispersed FLC matrix display enhanced alignment of FLC molecules for the superior performance in optical devices. The dielectric permittivity of FLC matrix has been observed to be decreasing with increase in concentration of GNPs as function of temperature due to the charge transfer properties between FLC and GNPs. The relaxation frequency is shifted to the low-frequency region in case of low concentration of GNPs in ferroelectric mesophase. UV–Visible absorbance of the synthesized composites is used to calculate optical density and skin depth of the materials. The phenomenon of surface plasmon resonance observed in GNPs has been employed to probe in the utility of the FLC driven optical waveguide designing. The experimental results may be utilized in the fabrication of opto-communication network device and optical sensors.

Single layer graphene: an alternative electrode material for ferroelectric liquid crystal based displays

ABSTRACTWe made comparative investigations on indium tin oxide (ITO) and single-layer graphene (SLG)-coated glass substrate as electrodes, specially for ferroelectric liquid crystal (FLC)-based system. We experimentally examined the comparative behaviour of important electro-optical FLC parameters for ITO- and SLG-based sample cells. The parameters are observed to be almost similar for both the cells. Interestingly, the value of threshold voltage is observed lower in SLG-based cell in comparison to that of conventional ITO/ITO cell. The presented results will definitely add a step to prove the suitability of graphene to be used as transparent electrodes in FLC-based display devices.

Study on alignment technique of ferroelectric liquid crystals for display application

ABSTRACTThe rubbing conditions are researched in terms of the rubbing cloth materials for ferroelectric liquid crystal (FLC) display application. Although cotton is generally used as the rubbing cloth, a good FLC molecular alignment can be obtained even in (semi) synthetic fiber clothes such as acetate, cellulose, and polyester. In order to obtain the good alignment without rubbing scratches, it is important to use a soft cloth. On the other hand, for a hard cloth, there is a possibility to obtain the good alignment by increasing the rubbing number and thus, polishing the alignment film surface.

Paper No P22: Fast Ferroelectric Liquid Crystal Display With Novel Photoaligned Layer

AbstractA novel composite photoalignment layer for ferroelectric liquid crystal (FLC) displays is explored. The key technique is to introduce a functional liquid crystal polymer into azo‐dye material with proper mixing. Bearing good alignment quality derived from the azo‐dye, the composite layer provides strong anchoring energy comparable to that of rubbed polyimide layers. Furthermore, by using a two‐step exposure process, the composite layer shows much better stability than that with a pure azo‐dye material. The photostability has been evaluated by the exposure energy needed to rearrange the orientation of SD1 molecules. The photostability is improved by more than 20 times using composited layer compared with pure SD1 material.

P.98: Novel Composite Photo‐alignment Layer for Ferroelectric Liquid Crystal Display

AbstractA novel composite photo‐alignment layer for ferroelectric liquid crystal (FLC) displays is explored. The key technique is to introduce a functional liquid crystal polymer into a rewritable azo‐dye material with proper mixing. Bearing good alignment quality derived from the azo‐dye, the composite layer provides strong anchoring energy comparable to that of rubbed polyimide layers. Furthermore, by using a two‐step exposure process, the composite layer shows much better stability than that with a pure azo‐dye material.

Method based on polarized infrared spectroscopy for the determination of the spatial orientation of transition dipole moments of a ferroelectric liquid crystal

A method to determine the spatial orientation of the transition dipole moments for ferroelectric liquid-crystal (FLC) molecules in the surface-stabilized FLC states by use of both conventional and oblique polarized infrared spectroscopy is proposed. It is found that the core moiety is tilted by an angle of about 7° to the surface of the cell windows.

A Novel Gray-Scale Method for Ferroelectric Liquid Crystal Displays Utilizing Ultra-Fine Particles

We have developed a novel gray-scale technique for ferroelectric liquid crystal (FLC) displays. This technique involves the addition of nanometer scale ultra-fine particles into the FLC mixture to produce micro domains, whose threshold voltages vary. Each domain has a different threshold for memory latching and is small enough to cover the full gray scale within one pixel element (less than 3 µm in diameter). Moreover, each domain maintains bistability, that is, this method doesn't inhibit passive-matrix driving. The voltage-transmittance ( V-T) curve of the cell depends on the particle-size distribution, such that if the particle-size distribution is sharp, the gradient of the V-T curve is small and vice versa. By X-ray diffraction analysis, wide tilt angle distribution of the smectic layers, which characterizes this nanometer scale particle-contained FLC, was found. The advantages of this technique are that an analog gray scale is possible and that the V-T curve can be controlled by selecting appropriate particles, which means no fundamental change in the fabrication process is required.

Synthesis and properties of optically active α-trifluoromethylbenzyl derivatives for ferroelectric liquid crystals

Abstract As new chiral dopants for ferroelectric liquid crystals (FLCs), some optically active α-trifluoromethylbenzyl derivatives were synthesized, utilizing optically active 3-(4-methoxy-phenyl)-4,4,4-trifluorobutanoic acid. The magnitudes of the spontaneous polarizations (P s) and the response times depended on the core structures and the type of linkage between the optically active and the core blocks. FLC mixtures containing the chiral dopants having an ether bond between the optically active block and the core blocks showed large P s values compared with those having an ester linkage, while the response times were inversely proportional to the values of P s.

Synthesis and properties of new chiral dopants containing a δ-lactone ring for practical ferroelectric liquid crystal mixtures

Abstract A series of new optically active δ-lactones were synthesized as chiral dopants for ferroelectric liquid crystals (FLCs). The response time of an FLC mixture containing 4 mol% (S)-2,2-dimethyl-5-[2-fluoro-4-(5-n-octylpyrimidin-2-yl)-phenoxy[methyl-δ-valerolactone was 25 μs at 25°C. (0–90 per cent change in light transmission, 10 V μm−1). The synthesis and properties of these materials as practical chiral dopants are reported.

Switching on stray electric fields in ferroelectric liquid crystal cells

Abstract In liquid crystal dot-matrix displays light may leak through the display area between the pixels. To obtain sufficient contrast this non-pixel area has to be made non-transmissive. For ferroelectric liquid crystal (FLC) displays this may be done by switching the material in the gaps between the picture elements to a non-transmissive state by the stray electric fields that occur during application of voltages to the pixel electrodes. This is experimentally studied for test cells with an electrically modified smectic layer structure. The gap region considered is an asymmetric environment of the FLC material, as the transparent conductive coating has been removed on one substrate, whereas on the other substrate a conductor covers the glass. The FLC molecules in the non-pixel area prefer to direct their dipoles towards the covered substrate. To switch the FLC material with the stray electric fields, it is a prerequisite to outweigh this preference. We made spatially resolved observations for various gap widths and various applied voltages on 2 μm thick FLC layers. With bipolar voltage pulses of 64 μs width each, amplitudes of about 25 V are needed to switch the FLC in 3·2 or 4·0 μm wide gaps. It was found to be more difficult to switch gaps that, are 7 μm wide than was anticipated on the basis of the results for 4 μm gaps. This is attributed to the surface polarization charge due to the FLC permanent dipoles built up at the FLC-glass interface. Experimental results supporting this explanation are presented.

Ferroelectric liquid‐crystal mixtures containing new chiral γ‐lactone compounds

Abstract— New chiral γ‐lactone compounds were developed as chiral dopants for ferroelectric liquid‐crystal (FLC) mixtures. They were found to induce fast response times when they were doped into achiral liquid‐crystal host mixtures. In addition, the effect of the molecular structure on the melting point and the helical twist properties in the nematic phase were investigated. Some FLC mixtures and their applications to FLC devices are described.

Synthesis and Properties of Optically Active α-Trifluoromethylbenzyl Derivatives as New Chiral Dopants for Ferroelectric Liquid Crystals

Abstract Optically active α-trifluoromethylbenzyl derivatives as new chiral dopants for ferroelectric liquid crystals (FLCs) were synthesized utilizing optically active 4,4,4-trifluoro-3-(4-methoxyphenyl)butanoic acid prepared by optical resolution procedures. The magnitudes of spontaneous polarization (Ps) and the response time depended on the type of the linkage between the optically active block and core blocks.

5,5-Dialkyl-δ-valerolactone Derivatives as New Chirai Dopants for Ferroelectric Liquid Crystals

Abstract (S)-2-(4′-Octyloxybiphenyl-4-carboxy)-5,5-dipropyl-δ-valerolactone showed interesting properties as the chiral dopant for ferroelectric liquid crystals (FLCs). The FLC mixture containing only 2% by mol of this compound exhibited the magnitude of spontaneous polarization (Ps) as large as 9.6 nC/cm2 and the response time as fast as 75 μs at 25 °C in the electric field of ±5 V/μm.

Synthesis and Properties of Optically Active α-Aryl-γ-alkyl-γ-lactones as Chiral Dopants for Ferroelectric Liquid Crystals

Abstract Optically active α-aryl-γ-alkyl-γ-lactones were synthesized from chiral epichlorohydrin in several steps and found to be good chiral dopants for ferroelectric liquid crystals (FLCs). Relationship between molecular structures and properties is discussed.

Synthesis and Properties of Optically Active α-Alkyl-γ-aryloxymethyl-γ-lactones as Chiral Dopants for Ferroelectric Liquid Crystals

Abstract Optically active α-alkyl-γ-aryloxymethyl-γ-lactones were synthesized from chiral epichlorohydrin in short steps and found to be superior chiral dopants for ferroelectric liquid crystals (FLCs).

Ferroelectric mixtures and their physico-chemical properties

Abstract The requirements for ferroelectric liquid crystals (FLC) for an application in fast-switching electro-optic devices are summarized. Typical molecular structures for FLC-mixtures are discussed. New non-chiral SmC-substances as well as some chiral dopants are shown. Important material parameters which are presented include spontaneous polarization, tilt angle, helical pitch in the smectic and cholesteric phase, rotational viscosity, response time, optical anisotropy and dielectric anisotropy. New developed broad range FLC-mixtures with SmC*-phases, SmI*-phases or SmA*-phases at room temperature are introduced.