Akio Mukoh

A Novel Preparation Method of Organic Microcrystals

Organic microcrystals ranging from several tens nm to µm in size of several chromophores were successfully prepared by simply dispersing ethanol solutions of compounds into stirred water, i.e. by a reprecipitation method. The size of microcrystals was found to depend on concentration of ethanol solutions, dispersing conditions, temperature and so on.

Organic photoconductive materials

A brief survey of the fabrication, evaluation and uses of organic photoconductive materials as xerographic photoreceptors is given. Included is a discussion of the basic material design roles required for successful operation of photoreceptor devices. The review includes present organic material classes used in commercial. copiers/printers and future potential of organic photoreceptors based on phthalocyanines and squaraines.

Highly conductive polyacetylene film prepared by the liquid crystal polymerization method under magnetic field

Abstract Advanced synthetic method of highly oriented polyacetylene film has been developed by applying magnetic force into a polymerization system consisting of nematic liquid crystals. Polymerizations were carried out at 10 – 13°C in order to keep the nematic phase under magnetic field of 2 – 14 kGauss. Polyacetylene films prepared showed high alignment of fibrils, providing not only crucial infrared dichroism in polarized infrared absorption spectra, but also the highest value of electrical conductivity with 10 4 S/cm order upon iodine doping.

Smectic C * Chevron Layer Structure Studied by X-Ray Diffraction

Layer structures in chiral smectic C (SC*) phases were studied by high-resolution X-ray diffraction. The existence of a chevron layer structure was confirmed even in thick cells such as 350 µm and even in a compound with the phase sequence of N*-SC*. Cells made by a SiO oblique-evaporation technique gave two diffraction patterns; a single peak was observed when the evaporation directions of top and bottom glasses were set in opposite directions (antiparallel), while two peaks were observed in the case of the glasses set in the same direction (parallel). Thus, the chevron structure was confirmed to exist quite generally except for in the SiO antiparallel cells.

Synthesis of highly-oriented polyacetylene film in a liquid crystal solvent

Abstract The synthesis of oriented polyacetylene films is investigated by using a nematic liquid crystal as polymerization solvent. Highly-oriented thin films are obtained under a flow of catalyst solution in which a nematic liquid crystal is used instead of common solvents such as hexane and toluene. Nematic liquid crystals that could be used as solvents for the Ziegler-Natta catalysts are limited due to their reactive substituents with the active species and/or the components of the catalyst. Among the available nematic liquid crystals, phenylcyclohexane type is stable in the presence of Ziegler-Natta catalysts. Since fibril alignment in the oriented films is found to be along the flow direction of the catalyst solution, it appears that the direction of fibril growth coincides with that of the liquid crystal orientation, which is caused by an alignment effect of the liquid crystal molecules under a flow of the solution. This new and simple method allows quite large highly-oriented films to be synthesized, which makes it possible to investigate various kinds of anisotropic properties of polyacetylene.

Correlation Between Bulk Orderings and Anchoring Structures of Liquid Crystals Studied by Scanning Tunneling Microscopy

The anchoring structures of a homologous series of liquid crystals, n-alkylcyanobiphenyls (mCBs: m=7-12), on molybdenum disulfide (MoS2) are directly observed by scanning tunneling microscopy (STM) in order to analyze the alignment mechanism of liquid crystals. Based on highly reproducible STM images, the anchoring structures of mCBs are clearly divided into two categories, a monolayer (single-row) type (7CB, 8CB, 9CB and 11CB) and a bilayer (double-row) type (10CB and 12CB). Here we propose the monolayer is the anchoring structure of a nematic phase, while the bilayer is the anchoring structure of a smectic phase. The correlation between bulk phase orderings and anchoring structures of liquid crystals is discussed from the viewpoint of surface-phase formation for the mCBs and different solid substrates.

New Room-Temperature Ferroelectric Liquid Crystals : Material Constants and Electro-Optic Properties

A binary ferroelectric liquid-crystal mixture having both room-temperature ferroelectricity and a large spontaneous polarization has been developed. The temperature range is from 20°C to 34°C. The spontaneous polarization is almost the same value, 4 nC/cm2, as that in DOBAMBC. Five material constants for the mixture; the transition temperature, spontaneous polarization, helical pitch, tilt angle and birefringence, are reported. A guest-host-type device was fabricated using the mixture, and some potential problems in the application of the materials to electro-optical switching devices are pointed out on the basis of the optical properties of this device.

Ferroelectric liquid crystal materials applied to guest-host type displays

Abstract Bistable ferroelectric liquid crystals (FLCs) suited for guest-host devices are described. Tilt angles of eight compounds and contrast ratios of the guest-host cells were measured as a function of temperature. The eight compounds were categorized into two classes. The first class exhibited the smectic A (SA) phase with a tilt angle of around 22°. The second class did not show the SA phase; the tilt angle was about 35° and almost constant over the temperature range of the smectic C(SC) phase. It was experimentally confirmed that the guest-host cell for the compound with the large tilt angle of 35° had a higher contrast ratio than 10. By using a binary system consisting of one compound from each class, influence of the tilt angle on bistability was examined. Increasing of the tilt angle improved not only the optical contrast ratio but also bistability.

Third-order optical nonlinearities of tetrakis-n-pentoxy carbonyl metallo-naphthalocyanines

Abstract Third-order nonlinear optical susceptibilities χ (3) of tetrakis- n -pentoxy-carbonyl (COO-C 5 H 11 ) naphthalocyanines containing central metal atom oxovanadium (VO), copper (Cu), zinc (Zn), palladium (Pd), and nickel (Ni) were measured by the third-harmonic generation (THG) technique. The metal atom substitution influences the third-order nonlinear optical susceptibility but the variation is less dramatic; oxovanadium cation was found to be the most effective. The order of χ (3) (−3ω; ω, ω, ω) at 2.1 μm wavelength was VONc > CuNc > ZnNc > NiNc > PdNc. The χ (3) (−3ω; ω, ω, ω) for VONc is 8.6 × 10 −11 esu, more than an order of magnitude larger than those of CuNc, ZnNc, PdNc, and NiNc compounds. A comparative study of optical and non-linear optical properties of processable metallo-naphthalocyanines is presented.

Synthesis, characterization, and properties of aligned polyacetylene films

Abstract Highly aligned polyacetylene films are synthesized by three different methods in which nematic liquid crystals are used as an ordered matrix solvent: Method 1, polymerization of acetylene is carried out in a quiescent nematic solution in which a Ti(OBu)4-AlEt3 Ziegler-Natta catalyst is dissolved homogeneously; Method 2, macroscopic alignment is attained by gravity flow of the nematic liquid crystal-catalyst system; and Method 3, the nematic liquid crystal-catalyst solution is aligned under a magnetic field. Characterization of these films is carried out through SEM observation and measurements of polarized visible and infrared absorption spectra. Results indicate that as-prepared films have highly aligned fibrils. Upon doping by I2 and AsF5, these films exhibit high electrical condactivity of the order of 104 S/cm.