Usami Kiyoaki

Photo-alignment efficiency of polyimide containing azobenzene in the backbone structure (Azo-PI) is significantly enhanced by exposing the precursor (polyamic acid: Azo-PAA) film to alkyl-amine vapor prior to photo-alignment. In this study, we have investigated the relationships between the alkyl-amine vapor treatment time, the swelling ratio of Azo-PAA films, and the photo-induced in-plane anisotropy. We found that: the Azo-PAA film swells on exposure to alkyl-amine vapor, and the swelling finally saturates; and the photo-induced in-plane anisotropy is correlated very closely with the swelling ratio. In addition, we pointed out the importance of the process order of alkyl-amine vapor treatment and photo-alignment.

Unusual behaviour of the dark conglomerate (DC) phase seen in an oxadiazole-based achiral bent-core liquid crystal, which has not previously been reported for the DC phase of other liquid crystals, is described. Under polarising optical microscopy, we see no domains of opposite handedness in the ground state of the DC phase. However, it shows unusual transformations when an electric field is applied to the system. On increasing the electric field, at first the domains of opposite handedness become visible and then they grow in size and slowly the sample transforms to a monochiral or single-handed form which is followed by a nonchiral state at very high fields. The threshold electric fields required to achieve these changes are temperature dependent and the transformations are seen irrespective of the frequency of the applied electric field (100 Hz to 5 kHz), type of the waveform (sine, square and triangular) and the thickness (1.5 μm to 15 μm) or the geometry (planar and twisted) of the device used. Further, there is no field-induced high birefringence texture observed even though sufficiently large electric field (~22 V/μm) has been applied across the devices. The nature of the behaviour is investigated by various techniques such as optical microscopy, conoscopy, circular dichroic and Raman spectroscopies, electro-optics and dielectric spectroscopy. The possible physical phenomena behind these changes are discussed in detail. © 2014 Taylor &amp Francis.

We have succeeded in controlling the pretilt angle of liquid crystal (LC) molecules over the whole range of 0 to 90 degrees by using photo-aligned blend films of two azobenzene-containing polyimides (Azo-PIs) with and without side-chains. The Azo-PIs were synthesized from pyromellitic dianhydride and a mixture of 4,4'-diaminoazobenzene and 4-(4'-propylbi(cyclohexan)-4-yl)phenyl 3,5-diaminobenzoate (PBCP-DABA). PBCP-DABA is a diamine to introduce a side-chain structure into the polyimide. Defect-free uniform LC alignment was obtained in the pretilt angle (theta(p)) ranges of theta(p) <= 11 degrees and theta(p) >= 78 degrees. Previously, we reported that the pretilt angle can be controlled using pure photo-aligned films of Azo-PIs with different molar fractions of PBCP-DABA. For the pure photo-aligned films, the defect-free pretilt angle ranges were theta(p) < 5 degrees and theta(p) >= 85 degrees. These results suggest that the azimuthal anchoring strength of the blend Azo-PI film is stronger than that of the pure films of Azo-PIs with side-chains, at least for the pretilt angle range from 5 to 11 degrees. We found that the defect-free pretilt angle range can be extended by using the blend Azo-PI films instead of the pure Azo-PI films. (C) 2011 American Institute of Physics. [doi:10.1063/1.3624767]

We have succeeded in inducing uniform alignment of liquid crystal (LC) molecules by using end-functionalized-perfluoropolyether (PFPE) (Fluorocur (R) made by Liquidia Technologies) films exposed to linearly polarized ultraviolet light (LPUVL). The average orientation direction of LC molecules was parallel to the polarization direction of LPUVL, which is opposite to most cases of other photo-alignment treatments. In the photo-alignment treatment, use of deep UV light and the existence of oxygen in the atmosphere was found to be important for inducing uniform LC alignment.

Deuterium NMR spectroscopy is widely employed to investigate the static and dynamic director alignment for low molar mass nematics contained in a thin sandwich cell. When the director is not uniformly aligned the appearance of the deuterium NMR spectra, recorded in the measurements, reflects the form of the director distribution. This occurs because the observed spectrum is a weighted sum of the spectra from all director orientations in the sample. In order to obtain the form of the director distribution function by simulating the spectra it is necessary to know how the spectral lineshape varys with the director orientation. As well as being of practical relevance, when the director distributes thermally with the average director orientation in multi domains, this contribution to the lineshape is of fundamental interest for nematic behaviour. Here we explore ways to vary the aveage director orientation using an electric field and employ this to measure the voltage dependence of the NMR lineshapes for the nematic phase of 5CB-d(2). This approach is investigated by using a computer simulation of the NMR lineshapes.

Deuterium NMR spectroscopy is widely employed to investigate the static and dynamic director alignment for low molar mass nematics contained in a thin sandwich cell. When the director is not uniformly aligned the appearance of the deuterium NMR spectra, recorded in the measurements, reflect the form of the director distribution. This occurs because the observed spectrum is a weighted sum of the spectra from all director orientations in the sample. In order to obtain the form of the director distribution function by simulating the spectra it is necessary to know how the spectral linewidths vary with the director orientation. As well as being of practical relevance, the angular dependence of the linewidths is of fundamental interest for nematic behaviour because it is related to factors such as molecular rotation, director fluctuations and orientational order. Here we explore ways to vary the director orientation. as a monodomain, using an electric field and employ this to measure the angular dependence of the NMR linewidths for the nematic phase of 4-alpha,alpha-d(2)-pentyl-4'-cyanobiphenyl as a function of temperature. (C) 2008 Elsevier B.V. All rights reserved.

We have succeeded in realizing an inclined homeotropic alignment of liquid crystal (LC) molecules by using photo-aligned films of a polyimide containing azobenzene in the backbone structure. To induce such an LC alignment, a side chain structure was introduced into the backbone structure. The LC pretilt angle, measured from the surface normal, could be controlled up to 1.75 degrees by varying the light exposure in oblique angle irradiation with unpolarized light. Its thermal stability was examined by annealing the LC cell at 100 degrees C. No change was observed in the pretilt angle even after annealing for 36 h, indicative of its excellent thermal stability. Since photo-alignment has patterning capability, the photo-aligned polyimide film is expected as a promising alignment film for multi-domain vertical alignment mode LC displays. (c) 2007 Elsevier B.V All rights reserved.

We have investigated the molecular orientation of glassy poly (9,9-dioetylfluorenyl-2,7-diyl) (PFO) layers formed on photo-aligned polyimide films with different in-plane anisotropy. The polyimide contains azobenzene in the backbone structure (Azo-PI), allowing us to control the in-plane anisotropy of the film by varying linearly polarized light (LP-L) exposure. The glassy PFO layers (similar to 30 nm thick) were obtained by annealing the samples at the liquid crystalline phase of PFO and then quenching them to room temperature. The degree of alignment of PFO was assessed by the polarization ratio of photoluminescence (PL). The PL polarization ratio increased rapidly with the LP-L exposure, and it reached 10 at 2.8 J/cm(2). Beyond this LP-L exposure, it became almost constant around 10.4. This PL polarization ratio was much higher than the absorption dichroic ratio of the underlying Azo-PI film. This result suggests that the degree of alignment of PFO is determined by its liquid crystalline nature. The saturation dependence of the degree of alignment is very useful for fabricating alignment patterns by a simple photo-mask exposure method. We have succeeded in fabricating 3 mu m line-and-space alignment patterns of PFO. (c) 2006 Elsevier B.V. All rights reserved.

We have succeeded in forming highly oriented poly[(9,9-dioctylfluorenyl-2, 7-diyl)-co-bithiophene] (F8T2) layers by using photo-aligned polyimide films. The polyimide (Azo-PI) contains azobenzene in the backbone structure, which allows us to optically control the alignment of the backbone structure. The photo-aligned Azo-PI films were stable to jl ylene (a solvent of F8T2) and to annealing at a liquid-crystalline temperature of F8T2. After annealing at 285 degrees C for 15 min followed by quenching to room temperature, the similar to 20 nm-thick F8T2 layer on the photo-aligned Azo-PI film showed a dichroic ratio of similar to 14 at 490nm (the absorption maximum), indicative of a high degree of alignment of F8T2. We conclude that the photo-aligned Azo-PI films are proper alignment films for F8T2.