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.
The efficiency of the conduction of photocurrent in discotic liquid crystals is known to depend on the quality of the
columnar organization. Solvents have shown to be able to influence the formation of wire structures on substrates
promoting very long and ordered wired formations or bulkier structures depending on the affinity of the solvent with
parts of the molecular structure of discotics. Here we present a study on the effect of solvents when the liquid crystal is
confined between two substrates with the columns running perpendicular to them, geometry used in solar cells. We
focused on toluene and dodecane, solvents that have shown to promote on substrates the formation of aligned and long
nanowires and bulk large and isolated fibers, respectively. The phase transition behavior indicates that toluene does not
interfere with the columnar formation while dodecane strongly influence increasing the disorder in the structure.
The self-organization of discotic liquid crystal molecules in columns has enormous interest for soft nanoelectronic applications. A great advantage of discotic liquid crystal is that defects can be self-annealed in contrast to typical organic materials. Through the overlap of molecular orbitals, the aromatic cores assemble into long range ordered one-dimensional structures. Very thin structured films can be obtained by spin-coating from solution and the resulting morphologies are strongly dependent on the interaction between discotics and solvent molecules. Toluene produces films formed by very long nanowires, spontaneously aligned along a common direction and over fairly large areas. These nanostructured films are a result of the interplay between liquid crystal self-organization and solvent driven assembly. The ordered nanowire structures exhibit improvement in the electrical properties compared to misaligned structures and even to pristine HAT5, deposited without the aid of solvent. In this study we show that the toluene-based deposition of discotic liquid crystals is advantageous because it allows a uniform coverage of the substrate, unlike pristine HAT5 but also thanks to the type of induced structures exhibiting one order of magnitude higher conductivity, in the aligned nanowire films, compared to bare HAT5 ones.
Drops or shells of a planar-aligned short-pitch cholesteric liquid crystal exhibit unique optical properties due to the combination of Bragg reflection in the cholesteric helix and a radial orientation of the helix axis. If such a droplet is illuminated from above, light is reflected into a continuous set of cones, the opening angles of which depend on where on the droplet the light hits its surface. For the wavelength that fulfills the Bragg condition the reflection is dramatically enhanced, yielding the light cones colored. A photonic cross communication scheme arises for certain angles, reflecting light back to the observer from a different droplet than the one originally illuminated. This gives rise to an intricate pattern of colored and circularly polarized spots. A number of interesting applications may be developed based on this pattern, e.g. in identification and authentication devices. We have carried out a detailed spectrophotometric analysis of the patterns, localized to individual spot maxima. A quantitative comparison between the measured spectra and the reflection wavelength expected from a model for the pattern generation allows us to conclude that the droplets are in fact not spherical but slightly ellipsoidal.
Lyotropic Liquid Crystals (LCs) are attractive materials as host systems for nanoparticles, in particular for carbon nanotubes (CNTs), due to the LC templating and dispersing action. Since carbon nanotubes have many remarkable properties their presence could also influence the aligning hosts and such effects need to be taken into account in CNTLC composites. CNTs can be dispersed efficiently in surfactant-based lyotropic hosts that can be removed after their templating action, being water based. However, residual surfactant has a detrimental effect on the nanotube properties and it becomes important to find ways to minimize its amount in CNT composites. In the present work we use, for CNT alignment, a lyotropic nematic LC host with a very low surfactant concentration, based on charge combination of cationic and anionic surfactant molecules. Small variations in the molar ratio of the two surfactants, still at a fixed total surfactant amount, yield a very different LC behavior. CNTs could be successfully dispersed in the host forming an overall low-surfactant composite. Interestingly, the presence of nanotubes strongly influences the behavior of the host, bringing a stabilization of the LC phase.
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.