"Ferroelectric smectic (SmC) phase" Anchoring effects on the polymer films in the liquid crystal (LC) display devices plays key role to create the restoring force to the black state for any types of display modes, such as IPS, STN, VA and OCB etc. On the contrary, we have designed the slippery interfaces in the homeotropic ferroelectric (SmC*) liquid crystals for the DH-FLC mode as walls wetted on the electrodes in the in-plane switching cell, and success to reduce the driving voltage keeping the ultra-fast response.
"Principle & Design" We have invented the new principle to produce the slippery interfaces on the glass plates or even nano-interfaces embedded in the materials such as PSChBP. Slippery interfaces are created by the disorder effect induced by the several types of frustration. For example, the impurities with surface affinity weaken or melt the liquid crystalline (LC) order near the interfaces, then boundary region of LC spontaneously play roles on the slippery interfaces. Therefore, the anchoring effect disappears, and molecular motion is lubricated by the slippery interfaces. Especially, change of the anchoring to the slippery condition can be controlled by UV illumination on localized azo dye surfaces.
"Evaluation" We measure the dynamics of surface director rotation under rotating magnetic field, and analyze the response of the surface director by changing the strength of the magnetic field and rotation speed of the cell. Therefore, we correctly evaluate the change of the anchoring condition which is related to the anchoring energy and viscosity of surface director. Anchoring phenomena is strongly dependent on the model of the slippery interface, the temperature and even the LC materials on the interface.
We designed the fast switching & low driving voltage principle with nano slippery interfaces in nematic gels. Confinement effect by the gel network can accelerate the response time of nematic due the localization of director motion as similar way to the cholesteric blue phase. However, the anchoring of the director on the gel network induces the driving voltage. Slippery effect on the nano interface of the gel network can reduce the driving voltage due to the lubrication of the director motion. Since azo dye acrylates are co-polymerized with nematic gels (Azo-NGel), we can demonstrate the UV-switchable nano-slippery interface on the nematic gels.
Dynamic Light Scattering (DLS) provides us the information of the dynamics of director rotation. Dispersion relation of the pure 7CB-T15 mixture completely satisfies the prediction of hydrodynamic modes in the nematic. On the contrary, the relaxation frequency of the Azo-NGel keeps fast response in the low wave-number region due to the confinement effect.
Electro-Optic response (EO) of the Azo-Ngel without UV illumination shows the serious increase of the driving voltage compared to the pure 7CB-T15 mixture. When the Azo-Ngel is illuminated by UV-light Slippery interfaces can be created by the trans-cis isomerization of the Azo dye of the side-chain on the nano network of nematic gels. EO under UV illumination shows the drastic reduction of the driving voltage keeping the fast response time. We have also confirmed that the dispersion relation of the UV illuminated Azo-Ngel is almost the same as that of Azo-Ngel without UV illumination by the DLS measurement. Thus, the confinement effect for the nematic gels is still effective after the slippery interface is created by the UV illumination.
We success to demonstrates that the acceleration of the response time is compatible with reduction of the driving voltage by the localization and lubrication of director motions due to the design of the nano-slippery interfaces in the nematic gels.
Anchoring effects on the polymer films in the liquid crystal (LC) display devices plays key role to create the restoring force to the black state. However, the chiral materials with spontaneous helix, such as deformed helix mode in SmC* (DH-FLC) or the polymer stabilized blue phase (PSChBP), can recover black state by rewinding motion of the helix itself. We have invented the principle and design of slippery interfaces, which has zero anchoring force for attached LC molecules on the interfaces, and confirmed the drastic reduction of driving voltage in DH-FLC mode of SmC* (<1 order) keeping the fast switching response (tau~50 micro sec). We have reported the lateral slippery interfaces consist of the phase separated liquid phases created by tran-cis isomerization of doped azo dye. It is not enough to the complete transmission of the light(I/I0~1) by applying the typical driving voltage (~1.0V/micro m) for current IPS panels. It is also problem that slippery interface become effective only just below the I-SmC phase transition temperature (TIC-T<20°). Here, we report new type of the vertical slippery interface realized by the spin coated swollen azo-LC gel films on the glass substrates. Under UV irradiation, trans-cis isomerization of the azo-dye co-polymerized in the azo-LC gel film, induces the vertical slippery interfaces by the disordering effect. Since the co-polymerized azo-dye cannot be dissolved into LC, the disordering effect is completely localized in the interface between swollen azo-LC gel and bulk SmC* material. Then the slippery interfaces can be stabilized over wide temperature range. We greatly improve the reduction of the driving voltage, I/Io=1, 1.0V/micro m for rather slow change of the driving voltage (tau~1msec 2.5msec pulse), I/I0=0.6, 1.5V/micro m for fast change (tau~50 micro sec, 250 micro sec pulse) by lubrication of intra and inter helix C-director rotation motions.
Liquid crystal is a representative soft matter, which has physical properties between those of conventional liquid and those of crystal in a temperature range above a melting point. A liquid-crystal display (LCD) employs the response of the liquid-crystal alignment to the electric field and is a key device of an information display. For common LCDs, the precise control of the initial alignment of LC molecules is needed so that a good dark state, thus a high contrast ratio, can be obtained. If the birefringence can be induced in the liquid phase by the application of electric field, it is of great use as a material for the LCD application. In this study, we will report a unique property of dichiral azobenzene liquid crystals: an electric induction of birefringence in a liquid phase of an antiferroelectric dichiral azobenzene liquid crystal. The optically isotropic texture changes into the homogenous birefringent texture by the application of the in-plane electric field above the clearing temperature of the liquid crystal. We find that one of the possible reasons of the induction of the birefringence in the isotropic phase is the electrically-induced increase of the phase transition temperature between the antiferroelectric liquid-crystalline and “liquid” phases, i.e., increase in the clearing temperature. The resulting birefringence can be disappeared by the irradiation of UV light, due to the photoinduced isomerization of the azobenzene compound, thus dual control of the birefringent structure, by the irradiation of light and/or by the application of the electric field, is achieved.
Biaxial nematic liquid crystals have attracted much attention from both fundamental and application points of view,
because the fast response based on the rotation of the minor director is expected. So far, different molecular designs have
been proposed for the emergence of the biaxial nematic phase. Among that, we have been interested in applying "preorganization"
concept on generating the biaxiality. Dimeric liquid crystal compounds have been prepared in line with
this concept in which two mesogenic parts are linked by the biphenyl connecting group. The pre-organized dimmer
shows an anomalous textural change, for vertically-aligned and free-standing film samples, at the smectic C (SmC)-
nematic (N) phase transition, in which the Schlieren texture of the SmC changes into the other Schlieren texture of the N
phase. There are two possible explanations for this textural change, i.e., the occurrence of the director change at the
SmC-N phase transition or the emergence of biaxiality in the N phase. The electric-field-induced birefringence has also
been measured in detail for investigating the biaxial nature of the sample.
Super-structures produced in the smectic molecular organization are reviewed, and the origin for the structures discussed,
in which it is emphasized that the frustration plays an important role in the emergence of the super-structures. Properties
and structures of mysterious smectic phases possessing chirality-induced super-structures are introduced, including
smectic blue and smectic Q (SmQ) phases that possess three dimensional (3D) structures. The molecular design on
stabilizing the 3D structure is proposed. The molecular orientations in the 3D structures are not so sensitive to the
external electric field due to an intricate smectic ordering, thus it has been difficult to imagine practical applications of
these structures. The SmQ compound possessing an azobenzene core in the molecular structure is designed and the
liquid-crystalline properties and photoresponse investigated. By means of the photoisomerization of the azobenzene
moiety, we demonstrate that the 3D structure of the SmQ phase can be controlled by light as an external stimulus,
suggesting a possibility for new applications utilizing the liquid-crystalline 3D structure.
An optically active liquid crystal compound, bis-[4’-(1-methylheptyloxy-carbonyl)-4-biphenyl] terephthalate, possessing two chiral centers at both peripheral ends was prepared, and the liquid-crystalline properties investigated. This compound showed a liquid crystal phase with a 3D superstructure of the defects, i.e., the smectic Q (SmQ) phase, between the antiferroelectric and isotropic liquid phases. Complicated x-ray diffraction spots appeared in the small angle region in the SmQ phase due to the formation of the 3D network of the defects, however, only broad scattering was observed in the wide angle region. Reducing the number of phenyl rings of this compound decreased the stability of the SmQ phase, thus the resulting compound just exhibited the antiferroelectric phase. Even in the isotropic phase above the SmQ or antiferroelectric phase of these compounds, a clear x-ray diffraction scattering was detected in the small angle region, suggesting a possible molecular pre-organization in the isotropic phase. Contact studies showed that another liquid crystal superstructure, i.e., a twist grain boundary phase, was induced by mixing these chiral compounds or by mixing the antiferroelectric compound with an achiral compound. Helical structures induced in the nematic phase were also examined for these and the related chiral compounds.
Aspherical mirror fabrication of HiNA set-3 projection optics was completed. By using a new polishing method, we successfully reduced low spatial frequency roughness (LSFR), mid spatial frequency roughness (MSFR) and high spatial frequency roughness (HSFR) compared with HiNA set-1 and set-2 projection optics. MSFR, which strongly affects the flare of the optics, was remarkably reduced to less than 0.2nm rms. HiNA projection optical system with the numerical aperture of 0.3 consists of two aspheric mirrors (M1 and M2). We had already fabricated two sets of the HiNA projection optics. The wavefront error (WFE) of the set-1 optics was 7.5nm rms and that of the set-2 optics was 1.9nm rms. We tried to reduce the WFE and flare in the set-3 optics. The target number of WFE of the set-3 optics was less than 1nm rms. The LSFR, MSFR and HSFR of the M1 of the set-3 optics were 0.25nm rms, 0.17nm rms and 0.10nm rms, respectively. The LSFR and MSFR are almost half values compared with those of the M1 for the set-2 optics. The HSFR was also reduced from 0.13nm rms (set-2) to 0.10nm rms (set-3). The LSFR and MSFR of the M2 were 0.25nm rms and 0.20nm rms, respectively. The estimated wavefront error calculated from these LSFR numbers is 0.7nm rms.
Novel non-symmetric dimeric liquid crystal, 1-(4-cyanobiphenyl-4'-yloxy)-11-[2-(4-octylphenyl)pyrimidine-5-yloxy]undecane (8YP11OCB), has been prepared and the physical properties investigated by means of optical microscopy, differential scanning calorimetry (DSC), X-ray diffraction and dielectric measurements. The crystal structure has been determined to understand microscopic behavior of the compound. Electro-optical properties for 8YP11OCB were compared to those for 1-(4-cyanobiphenyl-4'-yloxy)-11-[4-(5-octylpyrimidine-2-yl)phenyl-4"-oxy]undecane (8PY11OCB). 8YP11OCB with smaller dielectric anisotropy than 8PY11OCB was found to show a lower threshold voltage in the smectic A phase than 8PY11OCB. Crystal structure of 8YP11OCB indicates that three types of core-core interactions exist and that the enthalpy gained by the specific interactions stabilizes the molecular packing with large free volume in the SmA phase.
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