Hiroshi Awano

Homeotropic orientation of nematic liquid crystals induced by dissolving polypropyleneimine dendrimer having peripheral mesogens

A mixture of nematic liquid crystals (NLCs) with a small amount of a polypropyleneimine-based liquid crystalline dendrimer (D-6PC5 and D-6PPCN) exhibited spontaneous homeotropic alignment between the native glass substrates. This dendrimer-induced homeotropic alignment required two conditions; 1) the dendrimer completely dissolves in the NLC, and 2) a substrate surface is hydrophilic with the surface free energy above approximately 65 mN·m−1. The interdigitated-electrode cells without any surface treatment of the substrates were fabricated by filling with the LC dendrimer (D-6PC5)/nematic LC mixtures. They exhibited an electro-optical behavior when applying AC, vertical-alignment drive occurred in the cells. Based on these results, we speculated that the dendrimer adsorbs on the substrate surface and acts as a vertical alignment layer.

Structure and morphology of Langmuir-Blodgett films composed of a mixture of [tetrakis(cumylphenoxy)phthalocyanine]copper and octadecanol

Abstract The morphology and structure of Langmuir-Blodgett (LB) films of a 1:1 mixture of [tetrakis(cumylphenoxy)phthalocyanine]copper (CuPc(Cp) 4 ) and 1-octadecanol were studied by transmission electron microscopy, scanning electron microscopy, electron diffraction and X-ray diffraction. The LB film is a Y-type membrane, whose interlayer spacing is determined to be 23.5 A from the X-ray diffraction pattern. The average area occupied by the mixture of CuPc(Cp) 4 and octadecanol is 28 A 2 molecule −1 . To explain the interlayer spacing and the average area consistently, we propose a novel structure for the LB layer, which consists of a stack of eight CuPc(Cp) 4 molecules lying flat on the substrate, and eight octadecanol molecules penetrating through the stacking CuPc(Cp) 4 molecules in the peripheral space of phthalocyanine rings surrounded by cumylphenoxy groups. In the fractured LB film, many wide layers having crystallographical cleavage planes were observed. This result suggests that the LB film essentially consists of thin crystals.

Thin Films of (BEDT-TTF)2Cu(NCS)2 Prepared by an Electrodeposition Method*

Thin films of (BEDT-TTF)2Cu(NCS)2 are prepared by the electrochemical oxidation of BEDT-TTF at a large current density. The films are composed of numerous platelets, which are set on edge and loosely packed on the anodes. The X-ray diffraction suggests that the product contains both amorphous regions and κ-type and other crystals. The ESR and conductivity are discussed in terms of the presence of amorphous regions.

Magnetic orientation of side-chain liquid crystalline polyguanamines

Novel side-chain liquid crystalline polyguanamine with mesogenic groups (LCPGs) exhibited smectic liquid crystallinity. The polymers had an oriented structure under a magnetic field due to higher diamagnetic susceptibility of the mesogenic group. The mesogenic groups could be perpendicularly arranged on a glass substrate under a vertical magnetic field. Furthermore, they were obliquely aligned on the glass substrate by a tilt magnetic field. Tilt angles between the mesogen and the glass substrate were almost consistent with the directions of applied magnetic fields. Magnetic fields afforded various oriented structures, and the magneto-oriented structures were fixed in the samples.

Electrodeposition of quinhydrone

Abstract Quinhydrone crystals were electrochemically deposited at 2.0 V vs. Ag onto SnO 2 -coated glass substrates from aquous solutions of hydroquinone in the presence of NaCl, HCl, or NaOH. The crystals were observed with backscattered image SEM, and characterized with X-ray diffraction and IR spectroscopy. In situ visible absorption spectra were measured and a mechanism of deposition is discussed.

ESR study of dynamics of the phase transition in Wurster's blue perchlorate

Abstract Wursters blue perchlorate (WBP) crystal was prepared by an electrochemical oxidation, and its ESR spectra were measured over the range of 100–350K. Each spectrum shows a single line with an exchange-narrowed Lorentz shape. The ESR spectra have a maximum in the intensity at 193 K, and a minimum in the linewidth near the temperature, which corresponds to the well-known paramagnetic-antiferromagnetic phase transition. The linewidths show remarkable anisotropy, in particular, in the low-temperature region. The angular dependence of linewidth can be accounted for by a one-dimensional spin array along the a-axis of WBP crystal. The linewidth exhibits the most drastic decrease, when the field is applied along to the a-axis. This is because, at the transition point, the cation radicals would more fluctuate along the a-axis than along other axes, since the rearrangement of the Wursters blue radical cation occurs at the temperature along the a-axis.

Flow behaviours of liquid crystals on vertical alignment layers of polyimides

Nematic liquid crystals (LCs) dropped via micro-dispenser (3 μL) on a vertical alignment (VA) polyimide coated indium tin oxide glass substrate have been observed under crossed polarisers. The wettability between the LC and the VA polyimide layer was extremely low. The contact angle of the LC droplet was around 33° and the droplet diameter was much smaller than the LC on the parallel-aligned polyimide layer. The contact angle of the droplet increased, and the droplet diameter decreased, on increasing the molar fraction of the side group of the polyimide. The flow behaviour of the LC by assembling between the two substrates has been directly observed under crossed polarisers. The droplet spread out keeping a cross-extinction pattern during assembling. After assembling to a 5 μm gap, a dark field was observed in whole area on the polyimide alignment layer with 50 mol% side group. Increasing the side group enhanced aligning the LC perpendicular to the substrate, and no disclination appeared.

Flow behaviours of liquid crystal droplets on polyimide alignment layers

The flow behaviours of liquid crystal droplets on polyimide alignment layers and during assembling between two substrates have been directly observed. The droplet shape became elliptical with time on the rubbed polyimide layer, where the major axis of the elliptical droplet was parallel to the rubbing direction. Rubbing enhanced the wettability between the liquid crystal and the polyimide layer. During the assembling process, the liquid crystal droplets elliptically splayed out between two substrates assembled antiparallel. The liquid crystal molecules preferentially flowed parallel to the rubbing direction in a two‐step flow mode; the droplet diameter slowly increased at the first step, and then it rapidly increased at the second step. The two‐step flow of the droplet proved to be due to the thickness of the droplet dependent on the rubbing strength.

Electrocrystallization of a halogen-bridged mixed-valence platinum complex

Abstract Electrocrystallization of [Pt(en) 2 ][PtCl 2 (en) 2 ](ClO 4 ) 4 (1), which is a halogen-bridged mixed-valence platinum complex having Pt II ··· X − Pt IV − X ··· chains, is reported. Electrochemical reduction of trans -[PtCl 2 (en) 2 ]Cl 2 in an aqueous solution of perchloric acid at a potential of −1.5 to −1.6 V vs Pt counter electrode gave red needle crystals of (1) which are several mm long. The crystals appeared not only on the electrode but also away from it. On the other hand, electrochemical oxidation of a Pt II complex gave no crystals of (1) and the reason for this result is discussed.

Spontaneous homeotropic alignment of nematic liquid crystals induced by a double-armed side chain liquid crystalline polymethacrylate

ABSTRACT A liquid crystalline polymethacrylate having two cyclohexylphenyl mesogens on its side-chain (PMG0) was synthesized by the radical polymerization of the corresponding methacrylate monomer (MG0). PMG0 exhibited a smectic A phase around room temperature showing a focalconic fan texture in POM observations and a broad diffusion in a wide angle range of its WAXD profile. Upon slow cooling at −1 °C min−1 from the isotropic melt, PMG0 exhibited spontaneous homeotropic alignment between two native glass surfaces. A mixture of the commercial nematic liquid crystal (ZLI-4792) containing 1.0 wt% PMG0 also exhibited a homeotropic alignment, which easily covered hydrophilic surfaces such as glass or polyacrylamide.