Satoshi Aya

Liquid crystalline amorphous blue phase and its large electrooptical Kerr effect

An amorphous blue phase III with low and wide thermal range (∼20 °C) including room temperature is induced by doping a bent-core nematic with a strong chiral material. We confirm that the electrooptical response is due to the Kerr effect, with the Kerr constant being up to two orders of magnitude larger than conventional Kerr materials such as nitrobenzene.

Multiple nematic phases observed in chiral mesogenic dimers

A sequence of seven nematic phases has been observed in chiral mesogenic dimers, having odd number of carbon atoms in the spacer, thus a bent shape. The highest temperature phase is a chiral nematic (cholesteric) phase on heating or blue phases on cooling. The lowest temperature nematic phase expels the chiral twist and exhibits spontaneous bent–splay modulation.

Unusual temperature dependence of smectic layer structure associated with the nematic–smectic C phase transition in a hockey-stick-shaped four-ring compound

In a newly designed four-ring asymmetrical bent-core compound, we observed smectic-C-type diffuse layer reflection over the entire nematic temperature range. At the nematic–smectic C phase transition, a sharp layer reflection emerges in addition to the diffuse reflection with different layer tilt angles.

Stable electro-optic response in wide-temperature blue phases realized in chiral asymmetric bent dimers [Invited]

We report that an asymmetric bent dimer, consisting of a rod mesogen and a cholesterol mesogen linked by a flexible spacer with 9 carbon atoms, was found to form blue phases with a record-wide temperature range. Moreover, highly stable, fast electro-optic switching is possible. In addition to the stable Kerr effect, the electrostriction effect was also observed.

Are chiral dopants with higher twisting power advantageous to induce wider temperature range of the blue phases

We studied the relationship between the stability of the blue phase (BP) and the helical twisting power (HTP) of chiral molecules doped in a non-chiral bent-core liquid crystal. Contrary to common wisdom, HTP values were found not to directly affect BP stabilisation, i.e. a wide temperature range of BPs was obtained in mixtures containing chiral dopants with relatively small HTPs, whereas the mixtures containing high-HTP chiral dopants showed narrow BP temperature ranges. Moreover, in some cases, the narrow BPs even disappeared with increasing dopant concentration. In contrast, as expected, chiral dopant with large HTPs can easily induce BPs only by small dopant ratio; the minimum concentration necessary to induce the BPs is inversely proportional to an HTP value. As a cause of such unpredictable behaviour, packing effect between a host bent-core molecule and chiral dopants was discussed on the basis of the experimental observation of cybotactic clusters. Effect of UV irradiation for the BP stability was also examined.

Novel Bistable Device Using Anchoring Transition and Command Surface

A light-driven bistable device was fabricated using nematic liquid crystal (NLC) cells with bare glass and perfluoro-polymer (CYTOP) surfaces. The CYTOP surface induces a discontinuous anchoring transition, when a particular NLC (CCN-47) is introduced into the cells. By doping CCN-47 with a small amount of photoisomerizable azo-dendrimer molecules, the bare glass surface serves as a command surface, since the azo-dendrimer is spontaneously adsorbed on the surface. Using hybrid cells with such different surfaces, a homeotropic orientation was successfully converted to a hybrid orientation by very weak ultraviolet-light irradiation. Because of the bistability at a CYTOP surface, the hybrid orientation is retained.

Nanosize-Induced Optically Isotropic Nematic Phase

We fabricated, in a polymer matrix, liquid crystal (LC) nanosized droplets with a correlation length ξ of about 140 nm, which appear as an optically isotropic film. Differential scanning calorimetry (DSC) and light scattering measurements gave unambiguous evidences of an existence of nematic LC (NLC) order and fluctuation over a wide temperature range. The correlation length obtained by light scattering was consistent to the droplet size determined by a scanning electron microscope (SEM). The dynamic electro-optic (EO) response in such an isotropic NLC (IsoN) phase was found to be very fast, tens of µs, in a confined geometry because of the local short-range nematic order in the IsoN phase. This type of EO effect is very attractive for next-generation LC displays and light waveguides because of (1) very dark view in the absence of a field, (2) very fast response being independent of temperature and applied electric field, (3) gray-scale display capability with a constant response time, and (4) unnecessity of any surface treatment.

Highly Elastic Liquid Crystals with a Sub‐nanonewton Bending Elastic Constant Mediated by the Resident Molecular Assemblies

A surprisingly high bending elastic constant (K33 ) is obtained in a newly synthesized compound shown here. Mixtures containing a few percent of this compound confirm the influence of the unusual K33 values, and show an improved electro-optic response. The origin of the huge K33 is discussed based on the formation of a smectic cluster structure formed in the nematic phase.

Anchoring transition in a nematic liquid crystal doped with chiral agents

Anchoring transition in cholesteric liquid crystals (CLCs) was studied in this article. The orientational change is not simple in CLCs; instead of the orientational change of the helical axis, a variety of molecular orientations in cells such as planar, Grandjean, fingerprint, and homeotropic orientations were observed depending on chiral dopant, its concentration and temperature. It is proposed that the competition between helix forming power and preferential surface anchoring must be the origin of this phenomenon.

Thermodynamically Anchoring-Frustrated Surface to Trigger Bulk Discontinuous Orientational Transition

Surface-specific liquid crystal (LC) nanostructures provide a unique platform for studying surface-wetting phenomena and also for technological applications. The most important studies on LC properties are related to bulk alignment, surface anchoring, and so on. Here, we study an LC system with a nematic liquid crystal (NLC) on a perfluoropolymer-coated substrate, in which a discontinuous bulk orientational transition has recently been found. Using free-energy analysis based on experimental results of the newly-conducted grazing-incidence X-ray diffraction (GI-XRD) measurements, we have confirmed a thermodynamic growth process of smectic liquid crystalline wetting nanosheets on the surface and successfully explained that a frustrated surface of planar and vertical anchoring states accompanied by an elastic energy cost kinetically triggers the bulk reorientation in the first-order manner. This interfacial bottom-up process may offer a general insight into how interfacial hierarchical molecular architectures alter the bulk properties of matter thermodynamically.