Besides the current liquid crystal material developments for conventional LCD applications, intensive efforts to enlarge application fields of liquid crystals have been made. Here Polymer Wall LC, Holographic Displays, Smart Windows, Light Guiding and Smart Antennas were explained as promising examples for new application fields of liquid crystal materials. The current situation and challenges of liquid crystal materials development to materialize the new applications were summarized and discussed in this paper.
Head mounted displays (HMDs) have attracted much interest in recent years for their potential in technologies of virtual reality (VR) and augmented reality (AR). We have been focused on liquid crystal display (LCD) technologies for binocular-type HMDs. For obtaining high realistic sensations, we are now under development of the LCDs with high resolution over 1000 ppi (pixel per inch), fast response speed, wide-viewing angle, and high contrast ratio.
We are developing a novel type of energy-saving windowpane which autonomously controls solar transmittance by seasonal change. It consists of polymer dispersed liquid crystals (PDLCs) and thermally switches the transparent/opaque states in the principle of phase transition behavior of liquid crystals (LCs) aggregated in polymerized mesogens. We will present our latest results and issues from now on. Additionally we will introduce the analysis of energy saving effect of residential windowpanes and the comparison with other technologies.
Liquid crystal materials, which possess unique optical properties, have received attention for security technology. Moreover, nonuniformity or randomness has attracted much attention from a security perspective. Since optical textures in liquid crystals usually have nonuniformity, we have proposed an application of UV-curable nematic liquid crystal films with nonuniform optical textures to security devices. These devices are embedded in the artificial products requiring authenticity and the information read form each film should be unique. So, these nonuniform patterns of optical textures can be used as the identification information.
Thermodynamics has played an important role in science of materials. Since it applies any objects irrespective of their complexity, its application in combination with statistical mechanics is especially useful for complex systems. Such examples applied to liquid crystalline systems are introduced with some backgrounds outside liquid crystalline science.
In this lecture, I will talk about discotic liquid crystals of organic transition metal complexes synthesized and characterized by our group since 1978. The interesting mesophase structures and physical properties of the representative “metallomesogens” will be touched.
Transmissive liquid-crystal display (LCD) devices are being extensively used for man-machine interfaces. Each LCD possesses a backlight unit (BLU) which is an indispensable device for a LCD. In early stages of LCD emerging period (1985-1995), lack of light ray control and optical design concept were the main issues of BLUs. Based on the total internal reflection (TIR) and nearly frustrated TIR, the author eveloped micro-reflector (MR) and micro-deflector (MD) for light control media, i.e., light-guide plate (LGP) and optical cavity, to build-up an optical concept for BLU design. The BLU issues were solved and the luminance on the BLU increased by 70% and resulted in saving power consumption of the LCDs. In the meantime, MRs or MDs were patterned on metal sheets and novel fabrication process was developed to accelerate the mass productions of the LGPs by 8 to 10 times.
Anchoring phenomena at surfaces/interfaces have been receiving tremendous attention due to scientific interests in their multifariousness and complexity, as well as the desire to control itself for application even beyond liquid crystal (LC) display. From a common perspective, nematic LCs (NLCs) anchor more strongly to surfaces upon lowering temperature, mainly due to the stiffened endogenous order parameter and the enhanced NLC-surface interactions. Here, we explore an unconventional anchoring behavior of a NLC with negative dielectric anisotropy on a perfluoro-polymer surface. It was found that the polar anchoring coefficient (W) of planar orientational state decreases with decreasing temperature. When reaching a critical temperature at which W becomes nearly zero, the bulk orientation changes from planar to vertical orientational state discontinuously. We show that this behavior is mediated by surface-enhanced smectic wetting structures from both experimental and theoretical approaches.
Liquid crystal lens has been developed. Thin and light weight has been achieved by using thin glass produced by re-draw process. Driving voltage and disclination of the device are significantly improved by optimization of structure of al optimization for the liquid crystal lens.
We have developed a two-way multi-view 3D display combining a liquid crystal (LC) lens and a horizontally and vertically x times-density pixel (HVxDP) arrangement. The two-way multi-view display features the same display resolution in 2D and 3D modes and a quite small color moiré for landscape and portrait respectively when using the HVxDP arrangement. In this paper, we realized suitable 3D properties for achieving a good balance between 3D moiré and 3D crosstalk for landscape and portrait by a two-way LC lens with two kinds of focal lengths for the edge part and the center part of the lens.
We achieved a super low power consuming LCD panel with an n-FFS mode driven by IGZO-TFTs at low frequency. In this paper, we report the development of a new photo-alignment process for n-FFS, which prevents light-leakage and mura caused by conventional rubbing processes. In addition, we also developed high reliable liquid crystal and photo-alignment materials, which reduce flicker in low refresh rate driving. These technologies have already been applied to the Generation Eight factory, and are being adopted to small/middle sized LCDs for smartphones, tablet PCs, notebook PCs and so on.
We systematically studied the photo-switching of the polar anchoring at the substrate/LC interface of a photo-sensitive dendrimer-doped nematic LC. The polar anchoring energy at the interface upon photo-isomerization under illumination of UV and/or VIS lights was evaluated and discussed experimentally by means of polarization microscopy, birefringence measurements, optical second harmonic generation, and attenuated total reflection infrared spectroscopy, and theoretically based on the simple Rapini-Papoular model. We also demonstrate the continuous bulk orientation change by the photo-dynamic process through the fine control of the polar anchoring energy.
A negative type liquid crystal which aligns planer and perpendicular to the rubbing direction on a polyvinyl imidazole (PVIz) film surface is mixed with a neutral LC which aligns parallel. Alignment direction changes perpendicular to parallel to the rubbing direction with increasing the concentration of the neutral LC. An azimuthal anchoring energy is measured as a function of the mixture ratio of two LCs.
We numerically study the behaviors of nematic liquid crystal confined in orientationally heterogeneous checkerboard substrates. The director field on the surfaces prefers to align parallel to the surface yet orthogonal between the neighboring domains. We found bistable director alignments in the patterned substrates. The energy barrier between the two degenerated alignments is increased, as the unit size of the checkerboard pattern is increased and/or the system approaches the isotropic-nematic transition temperature. On the basis of the elasticity theory, we attribute the bistability to the spatial modulation of the director field due to the heterogeneous anchoring effect.
We tried to control heat-driven rotations of Ch LC droplets on a glass substrate by changing the surface anchoring with introducing azobenzene compounds as an alignment film. When irradiated by UV light, the azobenzene causes a photo-isomerization from trans to cis, which should decrease the order parameter of the adjacent LC. We investigated the rotational behavior of the Ch droplets as a function of temperature gradient (heat flow) and UV light intensity and found that the UV light not only changed the surface anchoring but also generated another torque to drive the droplets rotation.
We have developed a light-removable adhesive based on a unique carbon framework in a columnar liquid-crystal phase. The LC material shows a high cohesive strength and therefore displays heat-resistant bonding properties, while the photoinduced melting behavior results in instant photoseparation technology.
We prepared a ternary mixture of a cyanobiphenyl derivative possessing a semiperfluorinated alkyl chain (20 mol%), 4-butyloxy-4'-cyanobiphenyl (40 mol%), and 5-butyloxy-2-(4-octyloxyphenyl)pyrimidine (40 mol%). We then investigated the phase transition behavior using polarized optical microscopy, differential scanning calorimetry, and X-ray diffraction (XRD). The mixture was found to exhibit two modulated phases. Structure–property relationship in the amphiphilic compounds reveals that the modulated phases are induced by competition between an interdigitated structure stabilized by amphiphilic interactions and a monolayer structure by core–core interactions.
Triphenylene deriveatives with six alkoxyazobenzenne moieties at the periphery connected by ester linkages are unique liquid crystals which exhibit bimesomorphism of calamitic and discotic mesophases on both thermotropic and photo-induced manners. The alkyl homologues were found to show two types of mesomorphy depending on the chain length where one sees the mesomorphism change with a gap of phase transition parameters such as transition enthalpies. The optical texture observations indicate two types of conformers with lath-like and rod-like shapes of molecules exist in the SmA phase and the rod-to-disc shape change on cooling leads to characteristic change of optical textures for the aligned samples. XRD measurements with highly brilliant synchrotron irradiation for the aligned samples support the proposal conformation types and an averaged conformers of which shape is of neither rod- and lath-like even in the isotropic liquid phase.
We have synthesized multi-joint polymers composed of oligothiophene as a semiconducting arm and ferrocene as a free rotation joint. These polymers displayed a spectral red shift in electronic absorption spectra compared to the case in its reference compound, without considerable concentration effects on the spectral shift in a series of compounds. This observation indicates that an isolated polymer chain forms the folding conformation driven by the intrapolymer pi-stacking and rotational motion around the ferrocene units. In the solid state, these polymers self-assembled to form 2D sheets by intrapolymer pi-pi interactions and interdigitation of alkyl chains.
1,2-bis(4'-n-alkoxybenzoyl)hydrazine (BABH-n, where n is the number of carbon atoms in the alkyl chain) and 4'-n-alkoxy-3'-nitrobiphenyl-4-carboxylic acid (ANBC-n) exhibit bicontinuous Cub liquid crystalline phases having three-dimensionally periodic structure. We studied phase transition temperatures, phase structures, and molecular mobilities of the both compounds, confined in cylindrical nanoporous glasses with different diameters (50, 100, 200, 500 and 1000 nm) using DSC, synchrotron-radiated XRD, and ESR, respectively. As a result, when the pore diameter was decreased, interestingly, the phase transition temperature from Im3m- to Ia3d-Cubic phases increased although melting and clearing points were reduced. We considered this is due to restricted thermal expansion of the liquid crystalline compounds in the nanopores.
Recently, a chirality was found in the so-called “Im3m” phase, and Ungar and Tschierske et al. attempted to explain the emergence of the chirality on the basis of the triple network model, but the random placement of defects had to be assumed in the propagation of molecular twist. In this presentation, we propose a new chiral “Im3m” model with complete propagation of molecular twist; the problem has been resolved with a basic structure consisting of non-connected shells and a network proposed by the present authors. The second topic is that the chiral cubic phase is realized by mixing two achiral molecules forming the Ia3d-gyroid phase.
We prepared some amorphous blue phase (BPIII) materials doped with an asymmetric dimer (I-n) in which phenylpyrimidine and cyanobiphenyl units were connected via a flexible spacer. We investigated their phase transition behaviour depending on the parity of the spacer. The BPIII materials doped with a small amount of an even-membered asymmetric dimer exhibited a phase sequence of isotropic liquid–high temperature chiral nematic (N*H)–BPIII–low temperature chiral nematic (N*L). Applying electric filed in the N*H, it changed to the nematic phase. The nematic phase did not reverse to the N*H phase but changed to BPIII upon removal of the electric field. The BPIII materials with a large amount of an odd-membered asymmetric dimer showed the BPIII with a temperature range of more than 30 K.
Nematic liquid crystalline (NLC) core-shell microcapsules show the unavoidable orientational defects (disclinations) derived from the topological requirements of a 2-D sphere. We aim to control NLC microcapsules by using the response of the disclination to external-stimuli. For the sake of this, a microcapsule of NLC doped with a photo-responsive azo compound was prepared for UV-light-triggered release action of the microcapsule content; the core aqueous droplet was released to the outer phase through the disturbance of the nematic ordering locally induced by the UV-light irradiation.
Photopolymerization is commonly used for the solidification of materials in a liquid state. Here we use the method to stabilize a large number of topological defects in nematic liquid crystals. We experimentally visualize the director field which consists of defects of strength ±1. For a very low concentration of a reactive monomer, the array structure cannot be maintained when the field is switched off. However, to our surprise, a reproducible grid-like texture can be generated even if a high-frequency electric field is applied.
Bent-core materials exhibiting the B4 phase, when dissolved in organic solvents, formed gels with helical ribbons made of molecular monolayers and bilayers, whereas strongly deformed stacks of several layers were found in the bulk samples. The width and pitch of the helical filaments both increased with terminal chain elongation. It was also found that bulk samples were optically active, in contrast to the corresponding gels, which lacked optical activity. The optical activity of samples originated from the internal structure of the crystal layers rather than from the helicity of the filaments. A theoretical model successfully predicts these behaviors.
We introduced perfluorinated oil between the layers up to 50wt% in a smectic C liquid crystal having perfluorinated chain, called it “a hyper swollen smectic liquid crystal”, and investigated the swelling effect on the interlayer C-director correlation by dynamic light scattering measurement. It was found that the twist elastic constant related to interlayer C-director correlation strongly decreases in the hyper swollen smectic liquid crystal. This result suggests that perfluorinated oil prevents the direct collisions between layers among liquid crystal molecules, hence the interaction to maintain the interlayer C-director correlation between layers is weakened by the swelling effect.
Recently we reported that the viscosity of p-methoxybenzylidene-p'-n-butylaniline (MBBA) in the presence of electroconvection shows a characteristic decrease in the high-voltage regime. The decrease in viscosity seems to be attributed to the negative contribution of electric stress. To verify the conjecture, we have estimated the magnitude of the electric stress by the response of shear stress when an ac sinusoidal voltage was turned on and off. Then, it is found that the electric stress is negative and does not depend on the shear rate. Under sufficiently low shear rate, the viscosity becomes negative due to the electric stress.
An orientational control technique of nematic liquid crystals using ultrasound was investigated. An ultrasonic liquid crystal cell was fabricated; it consists of a liquid crystal layer with the thickness of 25 m sandwiched by two glass plates having two ultrasonic PZT transducers. By exciting PZT transducers, the flexural vibration modes were generated on the cell. The acoustic radiation force to the liquid crystal layer was generated and changed the molecular orientation, resulting the drastic changes of the transmitted light distribution. These results implied that the orientational direction of the liquid crystal molecules could be controlled by applying ultrasound.
Cholesteric liquid crystalline (CLC) phase has attracted much attention due to its unique photonic structures, in which the helical orientational structure affects the light propagation. Unlike other photonic materials, photonic structures of CLC materials are smoothly bendable. Here, we report the light propagation behavior in CLC emulsions as a photonic structure surrounded by curved interfaces.
The interaction between electrospun nanofiber and nematic liquid crystal has been studied. In our previous research, we reported the use of aligned nanofiber as an alignment layer in a twisted nematic liquid crystal device and homogeneous alignment liquid crystal device. In this reported, nanofiber is used to improve the response time of thick nematic homogeneous liquid crystal device. With increasing concentration of nanofiber, the decay time of the device decreased. We found that the relaxation time of the composite devices is independent of the device thickness but strongly influenced by the nanofiber concentration.
A small amount of azo-dendrimer molecules dissolved in a liquid crystal enables dynamic motions of defects around microspheres and even translational and rotational motions of microrods in a liquid crystal matrix under unpolarized UV light irradiation. These motions are intitiated by a light-induced trans-to-cis conformational change of the dendrimer adsorbed at the surface of microparticles and the associated director reorientation. The bending direction of the cis conformers is not random but is selectively chosen due to the curved local director field in the vicinity of the dendrimer-coated surface. Different types of director distortions occur around the particles, leading to different types of motions.
To solve some inherent problems of LC compound with negative Δε (N-LC), we have designed and synthesized novel N-LChaving polycyclic aromatic hydrocarbons. These compounds have quite larger values of negative Δε in comparison with conventional N-LCs. Mixtures including these compounds give lower viscosity and the response time of displays which were used is shorter than that of conventional N-LC.
Recently, ”in-cell” technology has been attracting people’s attention for improving LCD performance, in which optical components such as retardation films and/or polarizers are fabricated inside glass substrates. For the technology, the use of UV-curable LC materials combined with a photo-alignment method are expected to bring LCDs into further improvement in the performance. In this study, we had investigated to improving the optical performance of a coating-type polarizer that is made of UV-curable liquid crystal (LC) doped with a dichroic dye (dye-type polarize). We use a stacked layer of a cholesteric film and a quarter wave-plate to make almost linearly-polarized incident light to a dye-type polarizer, and the theoretical and experimental results are shown to demonstrate the usefulness of the method.
A new mode LCD based on in-plane switching of LC director configuration has been developed. The LC cell consists of two types of substrates, one of which has a near-zero azimuthal anchoring surface and electrodes and the other has a strong anchoring surface rubbed in the direction parallel to the comb-shaped electrodes. In the voltage-on state, the LC cell starts to arrange the LC director in twist configuration at extremely low threshold voltage and show high light transmittance in the whole pixel area including above the electrodes. The new mode LCD using this LC cell will exhibit higher transmittance and contrast ratio at lower driving voltage than the conventional IPS-LCDs; however, in the voltage off state, it involves a longer response time.
Structure of smectic E (SmE) phase of liquid-crystalline (LC) semiconductor PhBTBT10 was studied with molecular dynamics (MD) simulations.Based on the results, we proposed a structure transformation model between bilayer crystal and monolayer SmE phase.
We have investigated the liquid crystallinity, thin film fabrication, and FET characteristics of mono alkyl phenylbenzothienobenzothiophene (Ph-BTBT) derivatives having an oxygen atom in side chain in order to improve the solubility. Synthesized Ph-BTBT derivatives show highly ordered liquid crystal (SmE) phase and increase of solubility. It is found that polycrystalline thin film with uniformity and flat-surface morphology was easily formed using liquid crystalline films as a precursor by solution process. The FET mobility was evaluated from transfer characteristics of the FETs. Ph-BTBT derivatives having longer side chain, Ph-BTBT-12O-1, showed high FET mobility of 13 cm2/Vs. We conclude that the idea using alkoxy-substituted side chain can improve the solubility effectively, while keeping high FET mobility of over 10cm2/Vs.
A polymerizable liquid-crystalline perylene tetracarboxylic bisimide (PTCBI) derivative bearing a triethylene oxide chain was synthesized. The compound exhibited a dimeric columnar phase. The spin-coated films were polymerized via exposure to the vapors of trifluoromethanesulfonic acid. The polymerized thin films exhibited electrochromism, which was caused by the generation of anion radicals and dianions of the PTCBI cores. In addition, the polymerized thin films were doped in an aqueous solution of sodium dithionate. The electrical conductivity of the doped films increased to 10-5 Scm-1 because ionic species can penetrate the ion-conductive domains in the polymerized thin films.
Non-peripherally octahexyl substituted phthalocyanine (np-C6PcH2) and tetrabenzoporphyrin (np-C6TBPH2) were synthesized and characterized to study on the phase behavior and charge carrier mobility in the binary blend systems for ternary blend organic solar cells (OSCs). An ambiguous situation between pseudo hexagonal columnar mesophase (p-Colh) and rectangular columnar phase (Colr) was seen in the mixture of 1:1 blend from phase diagram and polarized optical microscopic images. The OSC device based on np-C6PcH2, np-C6TBPH2, and PC61BM (1:1:1 blend) showed higher performance than np-C6PcH2 and PC61BM-based solar cell by improved fill factor associated with semiconducting characteristic value.
Electro-optic effects of liquid crystal cells characterized by the two-fold high speed response will be demonstrated by devising utilized optical compensators in the following ways: in the Part I: Optically Compensated-Tunable Birefringence(OC-TB) a +A-plate is devised whose phase difference between the e-wave and the o-wave will be pi/2-a (a
We report electro-optic effects in a planarly aligned cholesteric liquid crystal (ChLC) using an interdigitated array electrode with a pitch of 10 m between adjacent electrodes. In a cell with a thickness of 10 m, the electrode products distribution of electric field intensities in the thickness direction of the cell because of the narrow pitch between electrodes. When the electric field was applied to a ChLC with planar alignment, the reflection band width of the ChLC was broadened. The maximum band width showed approximately 300 nm, which was three times wider than the original band width at zero field. The broadening of the band width is attributed to distribution of the helical pitch induced by the field-intensity distribution in the thickness direction of the cell.
We have proposed a hybrid alignment nematic liquid crystal cell using a polymer stabilized technology. In a polymerization process, a UV penetration depth is carefully considered, which results in a change of polymer morphology. The UV irradiation from a homogeneous alignment substrate side causes a polymer rich layer near the substrate and the stronger scattering in the on-state.
Cholesteric liquid crystals (ChLCs) exhibit a selective reﬂection band originating from one dimensional helical structure, and thus is expected to be used in practical application such as reflective displays. In this study, we focus on Helfrich deformation in ChLCs, which causes an undulation of a helical structure. Usually, the Helfrich deformation can be obtained only in a short time (less than 10 s) while applying an electric field, and therefore have had a serious drawback in device application. Here, we demonstrated a sustainable Helfrich deformation in a ChLC with a partially polymerized region, leading to the wide-range tuning of the SR band covering red-green-blue reflection.
We demonstrate a circular flow formation at a surface in homeotropically oriented nematic liquid crystals with a free surface by a focused laser beam irradiation. Under a weak laser power, a pit together with an associated circular bulge is formed; the Marangoni effect. Here a diverging molecular flow from the pit (thermocapillary flow) also induces the director tilt to the radial direction. With increasing the laser power, the pit becomes deeper, and eventually evolves to a circular flow associated with a deeper pit and subsidiary circular bulge or valley structures. This phenomenon is induced by escaping from excess deformation energy due to a bend deformation of the director.
We prepared a homologous series of liquid crystal trimers in which two cyanobiphenyl units and one octafluorobiphenyl unit were connected via flexible spacers, and investigated their phase transition behavior depending on the parity of the methylene spacer. All trimers showed a nematic phase. The trimers possessing odd-numbered spacers were found to exhibit phase separation, i.e., N–Cry and/or Iso–Cry, whereas those possessing even-numbered spacers did not show such an unusual phase coexistence. We discuss the structure–property relationship in the trimers.
Applications of thermotropic liquid crystals are mainly in display technologies. By doing so, anisotropic nematic compounds are doped with cholesteric derivatives to create twist structures, suitable for various switching modes. In this study, similar ideas are applied into a porphyrin derivative, i.e., C12TPPH2. C12TPPH2 under a polarized light microscope is known to show discotic lamella phases. In this study, C12TPPH2 was doped with the mesogenic and non-mesogenic additives, which resulted in new phase characteristics under a polarized light microscope, using a heating stage for temperature controlling. The chiral mesogenic derivatives were of oxovanadium and copper(II) complexes of chiral -diketone ligands, etc., and of pyrazole and pyroxyzole groups. C12TPPH2 was mixed well with an additive using dichloromethane as solvent. A few drops of the solution were placed onto a pre-cleaned microscope slide where the solvent evaporated. Finally, the dried sample was covered with a cover glass and placed inside a temperature controller. The sample slide was heated above clearing point and the textures were observed on cooling. Figure 1(a) shows ordinary textures of C12TPPH2 at the rim of the slide. However, at 2 mol% of chiral compound, the mixture exhibited a distinct texture showing some periodic textures similar to twist formations at the material boundary, Figure 1(b). It was also found that the pitches of the periodic textures were linearly depended on the concentrations of added chirals. Additionally, C12TPPH2 doped with some non-chiral additives were also investigated.
We prepared a homologous series of achiral liquid crystal trimers in which two phenylpyrimidine units and one biphenyl unit were connected via flexible spacers, and investigated the phase transition behavior and the phase structure using polarized optical microscopy (POM), differentical scanning calorimetry, X-ray diffraction (XRD), and atomic force microscopy (AFM). All the trimers were found to exhibit nematic and dark conglomerate (DC) phases. The AFM measurements reveal that the DC phases have different porous structures depending on the alkyl spacer length.