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Chiral discrimination of vapours plays an important role in olfactory perception of biological systems and its realization by artificial sensors has been an intriguing challenge. Here, we report a simple method that tangibly visualizes the chirality of a diverse variety of molecules dissolved from vapours with high sensitivity, by making use of a structural change in a periodic microstructure of a nematic liquid crystal confined in open microchannels. This microstructure is accompanied by a topological line defect of a zigzag form with equal lengths of 'zig' and 'zag.' We find that a tiny amount of vapour of chiral molecules injected onto the liquid crystal induces the imbalance of 'zig' and 'zag' depending on its enantiomeric excess within a few seconds. Our liquid-crystal-based 'chirality balance' offers a simple, quick and versatile chirality-sensing/-screening method for gas-phase analysis (for example, for odours, environmental chemicals or drugs).

The effect of chirality on the liquid crystal organization has been systematically investigated between (S,S)- and (R,R)-isomers of a dichiral azobenzene compound. The racemic mixture was found to show the cubic phase (Im3m), indicating that the studied compound shows the cubic structure without the effect of chirality. However, with increasing optical purity of the racemic mixture, the cubic (Im3m) structure changes into the tetragonal phases (I422 and I4(1)22), which have been known as the SmQ phases, via a chiral cubic phase (I432). This is the first example of "chirality-driven" cubic-tetragonal structural change observed in liquid crystal systems, which is experimental evidence showing the novel type of chiral effect that produces the anisotropy in the structures of soft materials. The emergence of the anisotropy, i.e., the cubic-tetragonal phase transformation, is also induced by means of photoinduced phase transition of the SmQ phases based on cis-trans photoisomerization of the azobenzene compounds.

We developed photo-healable composite gels consisting of liquid crystal, microparticles, and gold nanorods. Upon irradiation with near-infrared light, the temperature of the composite gels rapidly increased above a gel-sol transition temperature by the photothermal effect of gold nanorods. Then, we successfully performed photoinduced gel-sol transition of composite gels based on the phase transition of liquid crystals induced by the photothermal effect. In addition, we achieved photo-healing of surface cracks made on the composite gels by means of the photothermal gel-sol transition. [ABSTRACT FROM AUTHOR]

Organic–inorganic hybrid liquid crystal (LC) gels have been synthesised by the thiol-ene reaction of a multifunctional cyclic siloxane, 1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane (TVMCTS) and alkane dithiols, 1,6-hexanedithiol (HDT) or 1,9-decanedithiol (DDT), in LC matrices, 4-cyano-4ʹ-pentylbiphenyl (5CB) or 4′-n-octyl-4-cyano-biphenyl (8CB). The LC gels were prepared in an isotropic phase at 70°C or mesophases at 25°C using radical initiators. The phase transition temperatures from a mesophase to an isotropic phase of the resulting gels were lower than those of the original LCs. The gels containing 8CB (8CB gels) prepared at 25°C showed two phase transitions: smectic-to-nematic and nematic-to-isotropic transitions. By contrast, the 8CB gels synthesised in the isotropic phase showed only one phase transition from smectic phase directly to isotropic phase. Reaction conversions in the LC gels prepared at 70°C were higher than that in the gels prepared at 25°C. Scanning microscopic light scattering analysis of the LC gels cleared homogeneous small size mesh with a small amount of large defect. Polarisation micrographs of the LC gels showed framed optical textures derived from the LC molecules at room temperature. The LC gels containing more than 90 wt% of LC showed electro-optic response. [ABSTRACT FROM AUTHOR]

Abstract: We investigated the effects of the nematic and smectic A (SmA) phase structures of liquid crystalline matrices on the viscoelastic properties of microparticle/liquid-crystal composite gels. The storage (G′) and loss (G″) moduli of the gels were largely increased in gels containing SmA matrices with a layered molecular assembly. However, the critical strain at which the gel state transformed into the sol state by the application of mechanical strain showed no significant changes with variation in the liquid crystal phase of the matrix. These results indicate that the introduction of a layered molecular assembly could be effective for rigidification of composite gels, while maintaining their critical strains. However, the composite gels tended to show a metastable state when SmA matrices were used because G′ and G″ of the gels were close to each other in the entire frequency region. This behavior was in contrast to the gels with nematic matrices, which showed a larger value in G′ than that in G″. The metastable state of gels with SmA matrices was also reflected in the frequency dependence of G′ and in the deterioration of the recovery of the gel state after mechanical breakdown. [Copyright &y& Elsevier]

Abstract: We investigated photochemical transformation of asymmetric topological defects formed around water droplets dispersed in the azobenzene-containing liquid crystals. It was found that initial structures and the photo-induced phenomena of the defects were clearly affected by chemical structures of the azobenzene compounds. In quite strong homeotropic anchoring obtained by using the azobenzene compound with a long alky chain, the hedgehog was formed around the droplets at the initial state. When the anchoring strength was decreased by changing the carbon number of the alkyl chain, a novel asymmetric defect which will be an intermediate structure between the hedgehog and the Saturn ring was observed. The ionic groups had an influence on the photochemical transformation of the defects. The azobenzene compound with a smaller ionic group induced only a change in the anchoring strength, and a disappearance of the hedgehog was observed on the irradiation with ultra-violet light. In the case of the azobenzene compound with a larger ionic group, photochemical switching of the anchoring and the transformation into the boojums was achieved. The photo-induced phenomena could be qualitative explained by an effectiveness of the cis–trans photoisomerization depending on molecular areas of the azobenzene compounds determined by the ionic groups. [Copyright &y& Elsevier]

Photonic control of defect structures and colloidal chains has been performed in azobenzene-containing liquid crystals dispersed with glycerol or water droplets. When we dispersed the colloidal droplets into the host liquid crystals, we could observe, at an initial state, Saturn ring and hedgehog around the glycerol and water droplets, respectively, indicating that normal alignment of liquid crystal molecules was induced on the droplets by the adsorption of the azobenzene molecules onto the droplets. In the case of the glycerol droplets, we achieved photochemical manipulation of the defect structures between Saturn ring and boojums on irradiation with ultra-violet and visible light. For the water droplets, an inter-droplet distance of the self-organized colloidal chain could be controlled by changes of the defect size on the photoirradiation. Photoinduced structural changes in the topological defects can be explained by the modulation of surface anchoring of the droplets by means of the cis-trans photoisomerization of the adsorbed azobenzene molecules. [ABSTRACT FROM AUTHOR]

We investigated liquid-crystalline properties and photoresponse of a chiral azobenzene compound and found that it shows two kinds of highly-ordered liquid crystal phases. Studies on the optical textures and thermodynamic properties of the azobenzene compound suggest that the both mesophases are classified as the smectic Q (SmQ) phase which has been known as one of the chirality-induced three-dimensional (3D) liquid crystal phases. By the miscibility studies, one of the mesophases was confirmed to be T*I structure among the four structures of the SmQ phase. In a spectroscopic study of the chiral azobenzene compound in a tetrahydrofuran solution, it has been confirmed that a cis-trans photoisomerization can be induced by irradiation with ultra-violet light. Although the 3D structures are not sensitive to the applied electric field, we successfully demonstrate the “photo-switching” of these 3D structures by means of the photoisomerization. [ABSTRACT FROM AUTHOR]

We investigated photoresponsive behavior of azobenzene-containing liquid crystals dispersed with glycerol or water droplets. At an initial state, Saturn ring and hedgehog defects were formed around the glycerol and water droplets, respectively, indicating that homeotropic anchoring was induced by adsorption of the azobenzene molecules onto the droplets. For the glycerol droplets, we observed structural transformation between Saturn ring and boojums on irradiation with ultra-violet and visible light. For the water droplets, an inter-droplet distance varied by changes of the defect size on the irradiation. These phenomena would result from modulation of anchoring conditions by the photoisomerization of the adsorbed dyes. [ABSTRACT FROM AUTHOR]

Abstract: By modulating liquid-crystal alignment on a colloidal sphere, we successfully manipulated topological defects in glycerol-droplet/liquid-crystal emulsions doped with amphiphilic azobenzene derivatives. At an initial state, a disclination loop (Saturn ring) could be observed around the droplet, in which the azobenzene molecules should adsorb onto the droplet and liquid crystal molecules align normally to the surface of the droplet. On irradiation with ultra-violet light (λ =365 nm), the disclination loop was unfastened and transformed into two point defects called boojums. This should be attributed to the alignment change of the liquid crystal molecules from normal to planar arrangement triggered by trans-to-cis photoisomerization of the adsorbed azo-dyes. On irradiation with visible light causing cis-to-trans photoisomerization (λ =435 nm), the boojums went back to the Saturn ring reversibly. [Copyright &y& Elsevier]

We prepared a homologous series of dimeric liquid crystals, α-(4-cyanobiphenyl-4′-yloxy)-ω-[4-(5-alkylpyrimidine-2-yl)phenyloxy]alkanes (mPYnOCB), in which cyanobiphenyl and phenylpyrimidine moieties are connected via a flexible central spacer. We investigated the physical properties of mPYnOCB and of binary mixtures between the dimeric compounds. The interdigitated anticlinic smectic C (SmCanti) phase was found to be induced for some binary mixtures between the dimers with a different odd-numbered spacer. Furthermore, a striped pattern was observed in the SmCanti phase of a homeotropically aligned sample. The striped pattern was propagated when the temperature of the sample was varied. We discuss the correlation between the structure of the SmCanti phase and the appearance of the striped pattern. [ABSTRACT FROM AUTHOR]

Both peripheral ends of some straight-shaped mesogenic compounds, possessing a biphenyl or azobenzene as a central rigid core, have been systematically modified, and the effect on the liquid-crystalline properties investigated. A fluorinated moiety introduced into the peripheral alkyl chains stabilized the smectic phase, whereas that into the terminally positioned phenyl rings resulted in the appearance of the nematic phase. Introduction of phenyl rings into the middle of the flexible chains produced a well-defined smectic layered structure. Further introduction of another phenyl ring at each terminal end was found to show a significant effect on the determination of the clinicity. [ABSTRACT FROM AUTHOR]

We perform molecular dynamics simulations using a simple model system of liquid crystal substance on air-water interface. A system of soft spherocylinders, which do not show smectic C phase in bulk, exhibits a tilted smectic phase when interacting with a model water plane. We observe not only macroscopic properties such as the pressure-surface area curve, but also correlation functions and diffusions as well. [ABSTRACT FROM AUTHOR]

Liquid crystals (LCs) show an anisotropic nature in various aspects of optical and electronic properties. This anisotropy enables LC materials to be used as active media in display devices. Birefringence, an anisotropy in optical properties of LCs, is especially useful from the viewpoint of the change in refractive index induced by light. This is the principle of LC photonics, in which optical signals are processed with the aid of LC materials. In this article, various approaches are described to change the alignment of the LC molecules: 1) photochemically induced phase transition of LCs by photochromic reactions is an order to disorder transition and can be brought about in a time scale of micro- to nanosecond; 2) reorientation of LC molecules by means of linearly polarized light is a change in alignment of LC molecules that occurs within the LC phases and induces a large change in refractive index, but needs more time. Applications of LC systems as holographic materials are discussed. [ABSTRACT FROM AUTHOR]

Dynamic manipulation of droplets could be achieved by light in a nematic liquid crystal (LC) doped with photochromic azobenzene derivatives. On irradiation of ultraviolet light, the trans→cis photoisomerization drives a directional motion of the droplets towards the cis-rich region and assembled close-packed two-dimensional hexagonal colloidal crystals. This behavior is mainly attributable to the reduction of the droplet-LC interfacial tension, associated with the enhanced surface activity of cis isomers. We also performed photochemical assembly of tailored droplet arrays by projection of computer-generated images on the samples. The photoinduced manipulation of droplets will provide a versatile approach to microstructuring of LC devices. [ABSTRACT FROM AUTHOR]

A novel dichiral azobenzene compound which shows two kinds of highly ordered liquid-crystalline phases was prepared. One of the mesophases was found, by miscibility studies, to be a chirality-induced three-dimensional (3D) liquid crystal phase. We, for the first time demonstrate the photoinduced phase transition of the liquid-crystalline 3D structure. [ABSTRACT FROM AUTHOR]

Unique characteristics were observed in phase-type gratings which were formed in polymer liquid crystal (PLC) films. We have investigated the formation and the properties of the holographic gratings recorded in PLCs with azobenzene moieties (photoresponsive unit). Two types of PLCs were examined: homopolymers of azobenzene monomers (PALC) and copolymers with a tolane moiety (mesogenic unit with a high birefringence) in the side chain. The diffraction efficiency (η) was enhanced in the LC phase. We obtained the value of η of 31% while it was less than 1% in a glassy state in the Raman-Nath regime. This difference may be due to the modulation of refractive index (Δn) based on alignment change of mesogens in the PLC film. In addition, we attempted the holographic image storage of three-dimensional (3-D) objects in the PLC film. The 3-D object was reconstructed with high resolution (>5,000 lines/mm). [ABSTRACT FROM AUTHOR]