An azobenzene is one of photochromic compounds, and is well known to show trans-cis photoisomerization by irradiation of light with appropriate wavelength. One can control the molecular orientation of host liquid crystals by using this photoisozerization of the azobenzene compound doped. I will talk on the applications of this phenomenone for optical devices.
Effects of chirality, clinicity, and segregation on the liquid-crystalline structures and properties are overviewed, in which mysterious characteristics based on the anticlinic local order also be reviewed.
We develop a simple physical model using spheroidal molecules with chirality to control topological phases in a solid. Molecular rotation induces lattice distortion because of the anisotropy of intermolecular steric interaction, resulting in the emergence of the elastic field. We call this elastic field an emergent elastic field. We reveal that the emergent elastic field is a key to control helical and half-skyrmion structures. Utilizing the coupling between the emergent elastic fields and molecular orientations, we control topological phases by material parameters, temperature, and external perturbations. We also observe a novel re-entrant phase transition between the helical and thehalf-skyrmion phases.
Invariant tori are nested tubelike surfaces wound around by integral curves of three-dimensional solenoidal vector fields and form double-twist structures. Arrangements of invariant tori that resemble cubic rod packings are found. What twists generate each of the rod-packing-like arrangements of invariant tori is made clear. The realization of the arrangements in electromagnetic fields is discussed.
A different approach of utilizing liquid crystal which is in droplet form has received much attention from researchers in various fields. In this study, we investigate temperature phase trandition of cholesteric liquid crystal (ChLC) droplets on a water repellent glass surface. The ChLC droplets are formed using electrospray method. The temperature induced phase transition of the electrosprayed ChLC droplets exhibit size dependence.
Herein this presentation, we demonstrate a simple method for large-scale patterning of topological defects in nematic liquid crystals. Our approach is based on dragging of defects formed at the frontier of the Iso-N transition by shear flow or by temperature gradient control. The fabricated large-scaled topological patterns are surprisingly stable and memorized through the surface anchoring. Topological polymeric films are also fabricated on the basis of the present technique.
Hydrogen bonded liquid crystals (H-bonded LCs) have been applied to millimeter-wave and terahertz applications due to a small absorption coefficient. H-bonded LCs of 4-m-alkyl cyclohexane carboxylic acids (mCCA) and 4-n-alkylbenzoic acids (nBA) were mixed to be in a nematic phase at room temperature and those physical properties were measured by applying voltage of 1 kHz from the viewpoint of the device application. Bend, twist and splay elastic constants and dielectric constant were investigated in a homogeneous and twisted nematic cells.
Mechanical responses to electric stimulation in a liquid crystalline elastomer composed of cholesterol-derived mesogens were investigated. An electric-field-induced polar deformation resembling the motion of the flukes of a dolphin was observed in the temperature region of the pseudo-isotropic state of the elastomer prepared by cross-linking reaction under splay distortion. The emergence of polarization was also confirmed above the SmA* to the pseudo-isotropic phase transition temperature, whereas no polarization emerged in the SmA* phase. We tentatively conclude that the flexoelectric effect within splay distortion fixed by cross-linking caused the emergence of polarization and the polar deformation.
We report on the spatio-temporal observations of flexoelectric polarization using a time-resolved SHG microscope with an optical chopper. The experimental results were compared against the distribution of flexoelectric polarization computed from the results of the orientation simulation, and the effectiveness of the evaluation method for flexoelectric polarization was verified. The time-resolved SHG imaging shows that the SH intensity reaches its maximum at about 2 ms after the polarity of the applied square wave is reversed and then decreases afterwards. This is in good agreement with the time variation of the maximum value of the flexoelectric polarization computed by simulation.
In this study, we newly synthesized a sulfonated polyimide with oligooxyethylene side chains (APOS-PMDA). The oligooxyethylene groups increased the hydrophilicity of the side chains compared to the reported ASPI-2 with alkyl chains, therefore results in more water adsorption at high humidity range. Under humidified conditions, the newly synthesized polymer thin film exhibited lamellar structure driven by lyotropic liquid crystalline property. The APOS-PMDA thin film showed a proton conductivity of 0.11 S / cm at 95% RH and room temperature. These results provide a new perspective for exploring the influence of side chain properties on lyotropic liquid crystalline property.
Various biomimetic soft materials with structural hierarchies and stimuli responsiveness have been developed from organic materials. However, the creation of their counterparts consisting entirely of inorganic materials is challenging because the properties of such materials generally differ from those of living organisms. Here, we report thermally induced gel-to-gel transition of a liquid-crystalline hydrogel consisting of inorganic nanosheets and water. Since this transition accompanied internal structural changes, the optical and mechanical properties of the hydrogel changed reversibly and rapidly like sea cucumbers. By using a photothermal-conversion agent, this transition became operable spatiotemporally on photoirradiation.
Ferroelectric columnar liquid crystals (FCLCs) are promising materials for non-linear optics, actuators, and sensors. Though organic FCLCs have been realized by adjusting molecular shapes and hydrogen bond strength, in many cases, they are achieved at higher temperatures (> 100 °C) because strong intermolecular interaction inhibits switching of molecular dipole directions. Our group previously reported FCLC urea compounds possessing branched alkyl chains, and it was found that introducing branched alkyl chains is effective for polarization maintenance and lowering LC temperature. In this study, we present an unprecedented room-temperature FCLC achieved by a urea compound with longer branched alkyl chains. Further, we considered a constructive molecular design to realize FCLCs by molecular kinetics analysis.
Block copolymers have attracted great attention as nanotamplates utilizing sub-100 nm structures formed by microphase separation. It is necessary to achieve regulated microphase-separated structures to obtain desired functions. We have recently proposed a facile method for unidirectionally aligning microphase-separated structures simply by introducing a nematic liquid-crystalline polymer block, where the molecular alignment of liquid crystals induces the aligned nanostructures without guide patterns. In this study, we designed a block copolymer consisting of degradable polymer and nematic liquid-crystalline polymer blocks towards developing hollow nanotemplates with regulated alignment. We present the synthesis of the block copolymer and evaluation of their fundamental properties.
Excited-State Intramolecular Proton Transfer (ESIPT) is a process in which photoexcited molecules relax their energy through tautomerization by transfer of protons, resulting in the emission with a large Stokes shift from the tautomeric excited species. We have developed highly fluorescent ESIPT luminophores as a dopant for nematic LCs and disclosed their important properties-(i) high miscibility in host LCs, (ii) high fluorescent quantum yield over the visible region in host LCs, (iii) absorption window in visible region, (iv) lack of self-absorption, (v) lack of aggregation-cased emission quenching. The molecular design strategy and photophysical properties in LCs will be discussed in this lecture.
Herein, we report twist-bend nematic (NTB) liquid crystals (LCs) based on chalcogen linkages, thioether (C-S-C) and selenoether (C-Se-C). Due to the smaller bond angles of them than those of typical methylene (C-CH2-C) and ether (C-O-C), thioether- and selenoether-linked dimers with odd central spacers form more bent geometries than their methylene- and ether-linked counterparts, which are expected to be useful for formation of the NTB phase. The molecular design for forming the NTB phase, phase behavior, and the helical pitch examination using tender resonant X-ray scattering at the sulfur K-edge are described.
The display failure of FFS-LCD is an issue that has not been clarified. In order to understand this issue, it is necessary to understand the phenomena at the interface between the liquid crystal and the alignment film. In this study, since the device structure of FFS-LCD is complex, the device structure was simplified for the simulation study of the interface, and the dominant factors of the display failure were studied using COMSOL Multiphysics, a finite element CAE simulator software. As a result, it was found that in addition to the known effect of ion density, electric potential is another factor that affects the display failure. These factors affect the electric double layer at the interface and cause the display failure.
A ferronematic (NF) LC, in which the local nematic director is non-degenerate, is of great fundamental and practical interest. Since prediction on NF phase by Debye and Born 100 years ago, although an experimental evidence on the presence of NF phase in some polymer liquid crystals, in low molecular mass materials it has unrevealed. However, more recently, the long-awaited NF phase has been found in archetypal molecules, RM734 and DIO which would usher in an entirely new era in the history of liquid crystals. In this presentation, we would like to introduce the features and recent achievements on NFLCs.
Droplets of cholesteric liquid crystals coexisting with their isotropic phase are known to exhibit unidirectional steady change in their textures when subjected to a heat flux. Although the observation under a polarizing microscope is quite clear, it is still controversial whether the textural change is ascribed to rigid-body rotation of the droplet or pure director rotation. In this study, detecting the flow field, we confirmed the rigid-body rotation of the droplets even when the helical axis is parallel to the heat flux. Considering the ratio of the surface anchoring and the Frank elasticity and that of the elasticity and the Lehmann torque, we gave a reasonable explanation why the rigid-body rotation should be chosen.
A nonsymmetric core molecule with larger naphthalene and smaller benzene moieties at each side of the central dicarbonylhydrazine linkage and the same disiloxanyldecyloxy chain at both terminals formed both single-layered and double-layered core assembly modes in the Ia3d bicontinuous cubic phase as a single molecule system. The two assembly modes are, respectively, specific to symmetric molecules with the larger cores or smaller cores, and the “two-sided nature” was dependent on temperature and thermal cycle. The finding reveals that the core symmetry can control the core assembly and stability of the Ia3d network structure.
Recently, fast response displays are required for such as VR-HMD. We developed Short-range Lurch Control In-Plane Switching (SLC-IPS) LCDs to meet this requirement. In this paper, we describe the theory of SLC-IPS and its application, the characteristics in comparison with conventional IPS LCDs, and the electrode structure of SLC-IPS LCDs for high resolution.
We show some non-equilibrium dynamics observed in two-dimensional liquid crystals. The first example isthe orientational waves in illuminated Langmuir monolayers composed of azobenzene derivatives; the secondis the collective and unidirectional molecular precession in chiral monolayers under transmembrane watervapor transport; the third is the rigid-body rotation of an induced Smectic-E film driven by electron beamirradiation. In the 2D LC films with low symmetry, non-trivial cross correlation can often generate nonzerotorque, resulting in coherent and directional molecular motion.
In Axially polarized ferroelectric columnar liquid crystals (AP-FCLCs), the axial polarity of the columns can be switched by applying an external electric field, and is maintained after removal of the field. Although many examples of AP-FCLCs are known, very few studies have confirmed the polarization maintenance (PM) after removal of the field. We have been trying to realize PM-AP-FCLC phases using urea-based molecules since 2004, and we report our approaches and recent successes.
The properties of liquid crystals cannot be explained directly by their molecular fine structures. If the symmetry changes in phase transitions could be explained at the molecular level, it might be possible to understand how the molecular fine structures contribute to the phase transition behaviors. The molecular shape constantly changes both in a vacuum and in the condensed phase. In this study, we found that molecules in nematic phases conserve the uniaxiality of the phases as molecular shape distribution using molecular dynamics simulations.
Reentrant liquid crystals are low ordered phases, which reappear at lower temperatures than that of higher ordered phases. The possibility of reentrant liquid crystals appearing when the volume is kept constant is investigated, using the same interaction among all molecules. The method of canonical hydrostatic molecular dynamics simulation is used for this purpose. Canonical hydrostatic simulation results are compared with simulation results of isobaric-isothermal ensemble. Reentrant smectic A and hexatic smectic B phases appear in several model systems. Elastic instabilities and elastic oscillations in these systems are reported.
We present an all-atom molecular dynamics simulation study of the streptavidin protein binding at the monolayers composed of biotin-conjugated and biotin-free mesogenic molecules. The results indicated that the binding of the streptavidin to the monolayer was significantly stronger for monolayers composed of biotin-conjugated molecules than for monolayers composed of non-biotin-conjugated molecules. The analysis of the monolayer dynamics during the streptavidin binding also revealed that the dynamic behavior of the molecules composing the monolayers was significantly changed by the introduction of the biorecognition moiety into the mesogenic molecules. Moreover, streptavidin binding to the monolayer impacted the diffusion properties of the water molecules near the monolayer surface.
The dielectric dispersion of the nematic liquid crystal near the critical end point was measured under DC electric field. The permittivity increased near the phase transition temperature. To explain this result, the permittivity was calculated using Landau-de Gennes theory. It was clarified that the contribution of the soft mode becomes dominant near the critical point. In addition, the calculation results showed good agreement with the experimental results.
We have succeeded in the fabrication of gold nanosheets in a hydrophilic space inside highly separated bilayers in a hyperswollen lamellar liquid crystalline phase. The nanosheets can only grow in the in-plane direction due to the inhibition of the out-of-plane growth rather than the anisotropy of growth rates. We found that the width of the obtained gold nanosheets is proportional to the Reynolds number because the area of the bilayer in the hyperswollen lamellar phase depends on shear stress.
Here, we show that entropic elasticity fully recovers after photo-isomerization of azobenzene units incorporated in a nematic LCE. With the light-induced bent cis-isomers at room temperature, the degree of soft elasticity, viscosity, and adhesion are tangibly lowered. Mechanical responses rationalize that cis isomers unlock the frozen configurational degree of freedom by reducing nematic order in the same manner observed upon temperature increase. The present results not only unveil how the nematic interaction suppresses entropic elasticity leading to the soft state, but also offer a guide to tuning viscoelasticity toward dynamic mechanical applications.
Crosslinked liquid-crystalline polymers (CLCPs) containing azobenzene moieties are advantageous in fabrication of light-driven soft actuators because of their remote-controllability. However, CLCPs are insoluble because they form stable network structures by covalent bonds. Thus, the materials are not suitable for molding. In this study, we developed novel liquid-crystalline photomobile materials crosslinked by hydrogen bonding to improve their reprocessability. The resulting films showed photoinduced deformation reversibly upon irradiation with UV and visible light. This indicates that the photomobile materials we fabricated exhibit reversible photoresponsive properties and moldability.
Phase separation is a naturally occurring phenomenon in a blended mixture, in which a single phase composed of two or more components separates into multiple phases. The control of phase- separated structures is a key technology to develop advanced functional materials. Recently, we have serendipitously discovered the formation of periodic phase-separated polymer structures by the spatiotemporal photopolymerization using a slit of light. However, the formation mechanism of the structures is still unclear. In this study, aiming to explore the mechanism, optical analysis of periodic phase-separated structures was performed in polymer films fabricated under various photopolymerization conditions.
Chiral liquid crystals can be applied to asymmetric polymerization solvents to synthesis helical polymers. Synthesis of helical network polymers (HNPs) through photocrosslinking polymerization in chiral nematic liquid crystals (N*-LCs) has been reported. In this work, HNPs were synthesized in chiral smectic liquid crystals (SC*-LCs) as asymmetric medium. This is the first successful asymmetric polymerization using SC*-LCs. The HNPs showed a striated fan-shaped texture attributed to SC*-LCs and exhibited circularly polarized luminescence (CPL). The present HNPs have highly ordered structures compared to the HNPs synthesized in N*-LCs.
We synthesized cyclic chiral compounds by linking a photoresponsive bisbenzothienylethene moiety with an axially chiral binaphthyl moiety. The N*-LCs, prepared by adding the chiral compounds as chiral dopants to N-LCs, exhibited a reversible chirality inversion by virtue of extremely high fatigue resistance in photo-isomerization between open and closed forms of the bisbenzothienylethene moiety. Moreover, the mechanism of chirality inversion in photoresponsive N*-LCs was examined by comparing helical twisting powers (HTPs) of the analogous compounds.
We have fabricated arrays of bottom-gate/top-contact type organic field-effect transistors (OFETs) having active layers of poly(2,5-bis(3-hexadecylthiophene-2-yl)thieno[3,2-b]thiophene) (pBTTT-C16) and poly[4-(4,4-dihexadecyl-4H-cyclopenta[1,2-b:5,4b′]dithiophen-2-yl)-alt-[1,2,5]thiadiazolo[3,4-c]pyridine] (PCDTPT). The change in the field-effect mobility and the bias-stress stability by introducing nanogroove structures on the gate dielectric surface was investigated. Anisotropic charge transport and alignment-induced mobility enhancement were clearly observed for both semiconducting polymers. Under the same bias stress conditions, the electrical stability was evaluated and compared. The electrical stabilities of pBTTT-C16 OFETs were found to be higher than those of PCDTPT OFETs, independent of the presence of nanogroove structures on the gate dielectric surfaces.
We have been investigating the charge transport in organic semiconductors exhibiting smectic E phase. Wepropose a new charge transport model applying the quantum CT rate proposed by Lin et a1  with nuclear tunnelingeffects on the Gaussian energy landscape, which is used in Gaussian Disorder Model (GDM). The model can explainthe characteristic field and temperature dependence of mobility in the liquid crystals. We demonstrate how the staticdisorder disturbs poralonic transport and propose the concept how we can characterize the electron transport driven byNuclear tunneling with Correlated Gaussian Disorder.
We review our developed reflective and transflective LCD technologies, which provide high quality color image, low power consumption and good visibility. Our reflective LCD technology, based on a new twisted-VA mode and micro reflective structures, had excellent optical properties such as high reflectance, high contrast ratio and high NTSC ratio. Flicker-less 1Hz driving was achieved with applying IGZO-TFT technology and optimal panel designs. Considering the visibility in dark environments, a novel transflective LCD technology was developed based on the reflective technology. We successfully applied those technologies into LCD products the mass production of which has been started since 2020.
The development of solution-processed large-area flexible liquid crystal displays has a potentialfor further progress of organic electronics in the future. We have been studied fundamental technologiesbased on the functionality in nematic-phase liquid crystalline materials for flexible liquid crystal devices suchas orientational control of organic semiconducting single crystals, the novel device structure using structuraltransfer with imprint method and development of composite films composed of self-organizeddendrimer/liquid crystal for long lifetime device. In this paper, we report their techniques based on liquidcrystalline characteristics.
Measurement method of flexoelectric coefficients based on the transmission ellipsometry has reached a practical level for nematic liquid crystals (NLCs). It is considered that one of the possible reasons why reliable measurement has not been performed so far is the ionic pollution of NLC. It was concluded that two flexoelectric coefficients for splay and bend deformation can be determined at a practical level of reliability with one liquid crystal sample cell by devising the electrodes and the surface NLC alignment.
In recent years, much attention has been focused on swept light source for applications such as optical coherence tomography and LiDAR. Our research so far have investigated the improvement of lasing stability by means of periodic position change from a piezo stage and the method of fast tuning in lasing wavelength by means of cholesteric liquid crystal gels. In this study, we demonstrate swept light source based on cholesteric liquid crystal lasers by the combination of those methods on lasing stability and tuning, resulting in laser scanning system with a blazed diffraction grating.
Conventional photomobile polymer materials show macroscopic deformation upon irradiation with light only above room temperature. Thus, the driving temperature conditions are limited. It is desirable that photoinduced deformation should occur in a wide range of temperature. Therefore, we introduced new mesogens into photomobile polymer materials, such as those with bicyclohexyl moieties, and evaluated their photoresponsive properties in liquid nitrogen. The polymer films showed bending toward a light source when irradiated with UV light at room temperature. Then the bent films were immersed in liquid nitrogen and exposed to visible and UV light. We observed that they indicated reversible and repeatable deformation.
Recently, acceleration of materials development using computer simulations has attracted a great deal ofattention. In particular, density-functional calculations that do not use experimental data have gained greatexpectations in the context of new materials exploration. However, due to the limitations of densityfunctionaltheory in terms of computational accuracy and feasible system size, there are many challenges thatmust be overcome when considering practical applications. As a way to overcome these problems, the use ofquantum computers in the field of materials calculations has begun to attract attention. We are developingmethods for first-principles materials calculations that go beyond the limits of the density functional theoryby exploiting the performance of quantum computers to the fullest. In this talk, I will introduce our recentresearch and developed algorithms, and introduce the new world of materials simulation by using quantumcomputers.
We have developed a see-through head-mounted display (HMD) "BT-40 series".The product concept of the BT-40 series is to maintain the product size of the previous model BT-300, increase the angle of view (FOV) to improve visibility, and reduce power consumption and improve convenience as a mobile device. In this presentation, we will report on the technical improvements related to panel resolution improvement and power consumption reduction implemented in the Si-OLED panel mounted as an imager.
Recently, demand for super fibers with high strength and high modulus has been vigorous. Generally, super fiber has a rigid molecular structure based on an aromatic ring in many cases. Due to this molecular structure, it often has functionality such as high melting point due to high crystallinity and excellent chemical resistance. Among the super fibers, <Vectran> (polyarylate fibers) is attracting attention as fibers for industrial materials because they have many specific features. This publication introduces the characteristics of < Vectran> and their application development.
By co-polymerizing the azo-dye acrylate into PEG slippery alignment films, we succeed in arbitrary and reversible controlling the anchoring energy W of the slippery interface under UV light illumination. W is defined by the rotation angle of the surface director on the slippery interface when a magnetic field is applied.
A mean-field theory is introduced to describe nematic (N) ordering and phase separations in aqueous low-molecular-weight liquid crystalline molecules. We consider a physical bonding (or a hydrogen bonding) between the rod and solvent (water) molecules. Our theory predicts that the hydrogen bonds between the unlike molecules stabilize the N phase and take novel phase separations on the temperature-concentration plane. Upon increasing the number of functional groups on the rods and forming the physical bond with the solvent molecule, the stable N phase region is broadened on the phase diagram. We also find a miscibility window of the N phase and closed-loop coexistence curves with upper and lower critical solution temperatures near the N phase.
Ionic viologens are external-responsive compounds that can be reduced not only by electric field application but also by UV light irradiation. If the viologens can be given the inherent properties of liquid crystals, the application field of viologen will expand. In this study, viologen compounds with asymmetric rigid moiety were synthesized by introduction of an aromatic ring on one side of 4,4’-bipyridine and their liquid-crystalline (LC) properties were investigated. Compared with the extended viologen with a symmetric rigid moiety, the viologen with asymmetric moiety exhibited a low-ordered LC phase, and the crystalline-LC phase transition temperature was lowered by more than 100 °C.
Fabrication methods of polymeric liquid-crystalline microparticles and techniques to control their internal molecular alignment are important to develop micro-sized functional materials. We have fabricated chiral-nematic liquid-crystalline (N* LC) microparticles by dispersion polymerization and control internal molecular alignment. In this study, we reveal the mechanism of the monodomain alignment formation of polymeric liquid crystals over several μm2. From various experiments, we expected that the molecular alignment was determined during the nucleation-growth process of the microparticle formation during dispersion polymerization. The detailed mechanism of molecular alignment formation will be discussed.
In liquid crystals, special distribution of the refractive index can be modulated by controlling the molecular orientation. Thus, liquid crystals have been applied to the various optical materials such as diffraction grating, reflective device. To improve optical properties of the liquid crystal materials, it is very important to control the molecular orientation precisely. We have found in inducing the formation of periodic structure by using patterned light intensity gradient. Polymer concentration distribution induced by light intensity gradient is important for the formation of periodic structure. In this study, we aimed to investigation the mechanism of the formation of periodic structure.
It was found that the helical pitch in the SmC* phase becomes shorter when an ionic liquid is mixed with a ferroelectric liquid crystal(FLC). Based on the phenomenological theory related to the SmA-SmC phase transition by Pikin & Indenbom, related physical parameters to the helical pitch are considered to be the elastic constant, the spontaneous polarization, the tilt angle, the flexoelectric coefficient, and so on. Hence, we evaluated these physical properties experimentally, and discussed the mixing effect of ionic liquids on the helical pitch of FLCs.