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Free-standing films composed of several layers of chiral smectic liquid crystals (SmC*) exhibited unidirectional director precession under various vapor transfers across the films. When the transferred vapors were general organic solvents, the precession speed linearly depended on the momentum of the transmembrane vapors, where the proportional constant was independent of the kind of vapor. In contrast, the same SmC* films under water transfer exhibited precession in the opposite direction. As a possible reason for the rotational inversion, we suggest the competition of two origins for the torques, one of which is microscopic and the other macroscopic. Next, we tried to move an external object by making use of the liquid crystal (LC) motion. When a solid or a liquid particle was set on a film under vapor transfer, the particle was rotated in the same direction as the LC molecules. Using home-made laser tweezers, we measured the force transmitted from the film to the particle, which we found to be several pN.

Orientational correlations in Langmuir monolayers of nematic and smectic-C liquid crystal (LC) phases are investigated by molecular dynamics simulation. In both phases, the orientational correlation functions decay algebraically yet with the different exponents of 1.9 and 0.2 for the nematic and the smectic-C monolayers, respectively. The power law decay, i.e., the absence of long-range orientational order, means the both monolayers should be the ideal 2D system with a continuous symmetry, whereas the large difference in the exponents of power law gives rise to the crucial difference in their optical properties; the nematic monolayer is optically isotropic while the smectic-C monolayer exhibits an anisotropy on the length scale of visible light. Since the exponent is inversely proportional to the molecular exchange energy, the averaged molecular interaction in the nematic monolayer should be an order of magnitude smaller than that in the smectic-C monolayer, which is ascribed to the low molecular density and the weak molecular dipole due to the water molecule. The relation between the molecular interaction and the orientational correlation calculated for the 2D LC system offers much information not only about the 2D LCs but also on the bulk system. [ABSTRACT FROM AUTHOR]

Pre-organization effects are investigated for the laterally-connected liquid crystals possessing a biphenyl connecting group. The homeotropic texture of the N phase of a free-standing film sample was found to change into the other “Schlieren” texture on cooling even in the N phase, which then changes into the “Schlieren” texture of the SmC phase on further cooling. The possibility of the emergence of biaxiality in the N phase is discussed. [ABSTRACT FROM AUTHOR]

Hemispherical bubbles composed of smectic liquid crystals show an unusual deformation under DC electric field. When the lower voltage than a threshold is applied to the bubble on a substrate, it is elongated in the direction of the electric field and forms a semi-elliptical shape in the equilibrium. With the higher voltage than the threshold, the bubble becomes unstable and sometimes exhibits a periodic oscillation with repeating the elongation and shrinkage. Based on a simple equation of force balance, we analyzed both the static and dynamic deformations under DC field and successfully reproduced the observed behaviour. By the detailed analysis, we also determined the surface tension and the electric conductivity of the smectic bubbles. [ABSTRACT FROM AUTHOR]

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 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 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]

Molecular dynamics simulations were done for terminally alkyl and alkoxy substituted azobenzene liquid crystal (LC) molecules at an air-water interface using realistic (LC and water) molecular models. The simulation result were compared with those of a corresponding amphiphilic modification, i.e. terminal ω-carboxyalkoxy substituted azobenzene. Comparison with a LC with a different mesogen core, phenylpyrimidine, was also made. The interaction energetics were found to be more or less similar both in the alkyl and alkoxy terminated azobenzene and its amphiphilic modification, i.e. cohesive energy dominated over adhesive energy. In contrast, a large difference was found between alkyl and alkoxy terminated azobenzene and phenylpyrimidine LCs; cohesive and adhesive energy contributions were competitive in the latter molecule. [ABSTRACT FROM AUTHOR]

A phenomenological model of photo-induced traveling waves in liquid-crystalline Langmuir monolayers is presented. A linear stability analysis and numerical simulations of this model reveal that there are two oscillatory unstable modes with lower and higher wavenumbers which cause the traveling waves. The unstable mode with the lower wavenumber arises due to an interplay between the spontaneous splay deformation of liquid crystal order and the anisotropic photo-excitation of molecules. The other unstable mode with the higher wavenumber is concerned with the phase separation of the concentration field induced by the spontaneous splay deformation. The numerical simulations also show the coexistence between these two modes for certain parameter values. [ABSTRACT FROM AUTHOR]