Seiji Kurihara

Photocontrolled Translational Motion of a Microscale Solid Object on Azobenzene‐Doped Liquid‐Crystalline Films

On the move: Irradiation of azobenzene-doped liquid crystalline films with UV/Vis light results in the photocontrolled translational motion of microscale solid object on the surface, which occurs through cis-trans isomerization of the azobenzene unit. Irradiation with an Ar(+) laser (488 nm) resulted in precise control of the translational motion so that the particle always moved away from the irradiation position (see picture).

Graft copolymerization of vinyl monomers bearing positive charges or episulfide groups onto loofah fibers and their antibacterial activity

Ion exchange fibers with quaternary ammonium groups, phosphonium groups, or thiol groups etc., were prepared by graft copolymerization of vinyl monomers on loofah fiber which is one of the natural fibers. Methacryloyloxyethyl trimethyl ammonium chloride (METAC), tributyl-4-vinylbenzyl phosphonium chloride (TRVB), and epithiopropyl methacrylate (ETMA) were used as vinyl monomers. Graft copolymerization of METAC on loofah could be carried out in water using ammonium cerium (IV) nitrate. Graft copolymerization of TRVB and ETMA on loofah could be performed in water and water-dimethylsulfoxide mixed solution using hydrogen peroxide as an initiator, respectively. The optimum conditions for each graft copolymerization were investigated in detail. Ion exchange fibers (LE-TTA) having both thiol groups and triethylenetetramine side chains were obtained by treatment of L-g-ETMA (LE) with triethylenetetramine. LE and LE-TTA had high adsorption ability for silver ions. LE-TTA-Ag exhibited high antibacterial activity against E. Eoli and S. aureus, but LE-Ag did not. On the other hand, L-g-METAC and L-g-TRVB also exhibited high antibacterial activity against E. Eoli and S. aureus.

Effect of structure of photoresponsive molecules on photochemical phase transition of liquid crystals. I, Synthesis and thermotropic properties of photochromic azobenzene derivatives

Seventeen azobenzene derivatives were synthesized and their thermotropic properties were examined. They are classified into three groups. In the first group, 4-cyanobiphenyl moieties are attached t...

Preparation of resins containing phenol derivatives from chloromethylstyrene-tetraethyleneglycol dimethacrylate copolymer beads and antibacterial activity of resins

Copolymer beads (RCCS-4G) with many chloromethyl groups were prepared by treating macroreticular chloromethylstyrene-tetraethyleneglycol dimethacrylate (4G) copolymer beads with chloromethylether. Copolymer beads (RAAS-4G) with benzylamino groups were prepared by treating RCCS-4G with potassium phthalimide. Then the copolymer beads containing phenol derivatives were prepared by treating RAAS-4G with p-hydroxybenzoic acid (pHBA), 2,4-dihydroxybenzoic acid (DHBA), and 3,4,5-trihydroxybenzoic acid (gallic acid, GA) in N,N-dimethylformamide. The antibacterial activity of the obtained resins was examined against Escherichia coli and Staphylococcus aureus. Resins containing phenolic hydroxy groups of 2.3–7.7 mequiv/g were obtained. Antibacterial activity of the resins containing various phenol derivatives against E. coli or S. aureus increased in the order of RAAS-4G-GA > RAAS-4G-DHBA > RAAS-4G-pHBA. The resins containing phenol derivatives exhibited higher antibacterial activity against E. coli than against S. aureus and high activity even against bacteria in NaCl solution. Scanning electron micrographs showed that high antibacterial activity was brought about by the phenolic hydroxyl groups in the resin.

Permeation of solutes with different molecular size and hydrophobicity through the poly(vinyl alcohol)-graft-N-isopropylacrylamide copolymer membrane

Abstract Thermosensitive copolymers were synthesized by graft copolymerization of N-isopropylacrylamide on poly(vinyl alcohol) (PVA-g-NIPAAm) and the copolymer membranes were prepared by evaporating solvent from their Me2SO solution. The swelling ratio of the membrane in water increased gradually with decreasing temperature below 40°C and a considerable increase in the swelling was found below the LCST (33°C). The permeation rate of solutes through the PVA-g-NIPAAm membrane could be controlled by changing temperature. Polyethylene glycols (PEGs) with different molecular weight (400–6000) could be separated by changing temperature from 34 to 45°C. The permeation of butyl alcohols with different hydrophobicity through the slightly swollen membranes above the LCST was found to depend on not only the molecular size but also the hydrophobicity of solutes.

Azobenzene-Tethered Bis(Trityl Alcohol) as a Photoswitchable Cooperative Acid Catalyst for Morita–Baylis–Hillman Reactions

Incorporation of an azobenzene core into tethered bis(trityl alcohol) allows the photoswitchable arrangement of the two trityl alcohol units through photoisomerization of azobenzene. The differently arranged trityl alcohol units change their cooperative function to reflect the positional relationships, and thus, the activity as a cooperative acid can be controlled by light stimuli.

Thermal and Photochemical Control of Molecular Orientation of Azo‐Functionalized Polymer Liquid Crystals and Application for Photo‐Rewritable Paper

A photo-responsive multi-bilayered film consisting of azobenzene polymer liquid crystals (PA6Az1) and poly(vinyl alcohol) (PVA) has been prepared on a glass substrate by alternate spin coating of the polymer solutions. The reflectivity of the multi-bilayered film disappears by annealing at 80 °C. The disappearance of the reflection by the annealing is related to the thermal out-of-plane molecular orientation of PA6Az1 even in the multi-bilayered film, which leads to a very small difference in refractive indices between PA6Az1 and PVA. The reflectance of the multi-bilayered film is increased again by UV irradiation because of the transformation from the out-of-plane orientation to an in-plane random orientation. In this way, on-off switching of the reflection is achieved by combination of the thermally spontaneous out-of-plane molecular orientation and following photoisomerization of PA6Az1 comprising the multi-bilayered film.

Optical shutter driven photochemically from anisotropic polymer network containing liquid crystalline and azobenzene molecules

Polymer-dispersed liquid crystal(PDLC) with macroscopically uniaxial molecular alignment containing azobenzene molecules was produced. The PDLC was transparent because of this alignment. Upon photoirradiation to cause trans-cis photoisomerization of azobenzene molecules, the PDLC became translucent even at 30 °C. The PDLC system does not require the use of polarizers and electrodes to fabricate optical devices. The light scattering is ascribed to a biphasic morphology in the system produced transiently by means of the photochemical phase transition.

Isothermal phase transition of liquid crystals induced by photoisomerization of doped spiropyrans

The phase-transition behaviour of mixtures of liquid crystals (LCs) and photochromic spiropyran derivatives, induced by isomerization of the guest molecules, has been investigated. Two types of spiropyran derivatives were employed: normal spiropyrans which are stable in the closed form (spiropyran form; SPF) and open-form (merocyanine form; MCF) stabilized derivatives. These spiropyran derivatives were doped into two LC compounds: 5-cyanobiphenyl (5CB) and 4-butoxyphenyl-4′-ethylcyclohexanecarboxylate (ECH 204). SPF-Stabilized derivatives exhibited photoisomerization behaviour from SPF to MCF in LC media which was accompanied by an isotropic (I) to nematic (N) phase transition of the mixtures. On the other hand, an N → I phase transition of the mixtures was observed when the MCF-stabilized spiropyran doped in both LCs was photoisomerized from MCF to SPF. The result was interpreted in terms of shape anisotropy of the guest molecule associated with each isomer of the spiropyrans.

Photocontrolled manipulation of a microscale object: a rotational or translational mechanism.

In this paper the photocontrolled manipulation of solid materials on the surface of a liquid crystalline thin film is described. Three different types of films namely cholesteric liquid crystal (ChLC), compensated nematic liquid crystal (NLC) and nematic LC were used. The rotational and translational manipulation of the microscale solid object was induced by irradiation of light and mode of manipulation (either translational or rotational) was changed by changing the isomer of the azobenzene compound used to make the film. Rotational motion of the object was observed on the ChLC and compensated NLC films containing chirally pure azobenzene compound. The direction of rotational motion was controlled either by changing the optical isomer of the chiral azobenzene or by changing the irradiating light (from ultraviolet to visible). When racemic mixture of the chiral azobenzene compound was used, a translational motion of the object was observed. Even though the direction of the translational motion can be controlled by controlling irradiation position, more facile and precise manipulation of the objects was possible by spatially controlled irradiation of Ar(+) laser and diode UV laser.