Prof. Yuka Tabe Profile

Prof. Yuka Tabe

at Waseda Univ

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Proceedings Article | 8 February 2012 Paper

Pre-organized liquid crystals: biaxial nature of laterally-connected dimer

Isa Nishiyama, Yuka Tabe, Jun Yamamoto, Yoichi Takanishi, Yoko Ishii, Hiroshi Yokoyama

Proceedings Volume 8279, 827903 (2012) https://doi.org/10.1117/12.913573

KEYWORDS: Liquid crystals, Molecules, Birefringence, Molecular interactions, Physics, Active optics, Glasses, Thin films, Digital image correlation, Applied physics

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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.

Proceedings Article | 9 May 2007 Paper

Photochemical manipulation of colloidal structures in liquid-crystal colloids

T. Yamamoto, Y. Tabe, H. Yokoyama

Proceedings Volume 6587, 658707 (2007) https://doi.org/10.1117/12.722656

KEYWORDS: Liquid crystals, Particles, Transmittance, Ultraviolet radiation, Opacity, Saturn, Optical spheres, Polymers, Modulation, Molecules

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We investigated photochemical manipulation of physical properties and colloidal structures in liquid-crystal (LC) colloids containing azobenzene compounds. In a LC suspension where polymeric particles were dispersed in a host LC, we achieved photochemical control of light-scattering properties of the suspension. In a nematic phase, when the suspension was sandwiched with two glass plates, the film became opaque. This would be attributable to an appearance of both multidomain structures of LC alignment and mismatches of refractive indices between the materials. The opaque state turned into a transparent one when a nematic-to-isotropic phase transition was induced by the trans-to-cis photoisomerization of the azo-dye. This will result from a disappearance of both the multidomain structures and the refractive-index mismatches in the isotropic phase. The transparent film went back into the initial opaque film when the nematic phase was obtained by the cis-to-trans photoisomerization. In a LC emulsion in which glycerol or water droplets were dispersed in liquid crystals, we examined photochemical change of defect structures and inter-droplet distances by the photochemical manner. At the initial state, Saturn ring and hedgehog defects were formed around the droplets. For the glycerol droplets, we observed structural transformations between Saturn ring and boojums on irradiation with ultra-violet and visible light. For the water droplets, the inter-droplet distances varied by changing defect size on the irradiation. These phenomena would result from modulation of anchoring conditions of the droplets by the photoisomerization of the azo-dyes.

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