Key Engineering Materials Vols. 428-429

Abstract: Considering flexoelectric polarization, the equilibrium equation and boundary condition for tilt angle are derived. The influence of flexoelectric polarization on cell with different anchoring for the two substrates (i.e. a non-symmetric cell) is investigated. We show that, the easy direction is changed by flexoelectric polarization. The planar anchoring cell may equivalent to hybrid aligned cell under certain conditions. The influence of flexoelectric polarization on the director distribution is simulated by numerical method.

Abstract: Banana-shaped liquid crystals can self-assemble themselves into one kind of thin films in which periodic modulation of the refractive index can be developed. When a beam of light is shone onto the thin films, diffraction patterns can be formed. In this work, the diffraction equation is derived for one-dimensional diffraction gratings formed by banana-shaped liquid crystals.

Abstract: The spherulites’ morphology and melting properties of the poly(trimethylene terephthalate) formed in limited space at specific temperatures was studied by the polarized optical microscopy (POM). The results suggest that the spherulites’ morphology depends strongly on the temperature. When the isothermal crystallization temperatures increase from 190 to 225 oC, the spherulites’ morphology continuously changes in the following order: nonbanded → regular banded → serrated banded → nonbanded spherulites. Furthermore, the band spacing increases with the crystallization temperature. Heating the banded spherulites will cause them melt as well as the changing of the bandings, especially the bandings changes in the following order: clear → faint → clear → disappear in a certain range of temperature, which is proposed for resulting from a lamellar melting-recrystallization-remelting mechanism.

Abstract: The laser diffractions phenomenon of surrounding bubbles of lyotropic liquid crystal formed by sodium dodecylsulfonate were investigated with polarized optical microscope and helium-neon laser, respectively. The eleven orders of diffractions can be observed when a beam of helium-neon laser is perpendicularly incident on the surrounding bubbles of lyotropic liquid crystal formed by sodium dodecyl sulfonate. The wavelength of the incident light is 633nm. And we have calculated the periodicity, p, of the grating was 0.211mm, and the small diffraction angle was 0.1146o. So we have simulated the microstructure of surrounding bubbles in the lyotropic liquid crystal formed by sodium dodecyl sulfonate.

Abstract: The alignment of 2, 3, 6, 7, 10, 11-hexapentaloxy triphenylene (HAT5) on ITO glasses was investigated by polarizing optical microscopy, differential scanning calorimeter, X-ray diffraction and scan scanning electron microscope in this study. The results showed that the alignment of 2, 3, 6, 7, 10, 11-hexapentaloxy triphenylene can be fixed at room temperature by heating the sample to the isotropic temperature and annealing at 100°C overnight and then cooling slowly back to room temperature; the ordered arrangements of the micro structures are disconnected. The disconnection of the microstructure and the size of columnar assemblies can also be confirmed from the SEM observations.

Abstract: . We demonstrate that banana-shaped molecules 1,3-phenylene bis(4-methoxybenzylidene amine) can assemble themselves into diffraction gratings when the melt of the banana-shaped compound, which was sandwiched between two pieces of glass substrates, is cooled to room temperature. Polarizing optical microscopic characterization shows that a pattern of periodic modulation of the refractive index can be developed in the thin films formed by the banana-shaped compound. Despite the gratings are groove free, their optical properties are the same as classically ruled gratings. Our work provides an alternative method for manufacturing diffraction gratings by harnessing the self-assembly of banana-shaped molecules.

Abstract: This work reports the photo-alignment effect in a liquid-crystal film doped with nanoparticles and azo-dye. Vertical alignment induced by the nanoparticles polyhedral oligomeric silsesquioxanes (POSS) can be switched to homogeneous alignment by the absorption of photo-excited azo-dye. Both electro-optical and surface properties are analyzed to verify this effect. Using this photo-alignment technique in nanoparticle- and azo-dye-doped liquid crystal, the phase grating is also demonstrated. The diffraction efficiency is related to the polarization of the probe light and can be controlled by applying voltage. Both nanoparticle- and azo-dye-induced vertical and homogeneous alignments are non-contact aligning methods. Thus, the technique based on dopant-induced alignment has potential for practical applications.

Abstract: We demonstrate that a bent-core liquid crystal 1,3-phenylene-bis(4-butoxybenzylidene amine) can write the Chinese character 人, which means a person in English, when the bent-core compound gets cooled from its isotropic phase. The polarized optical microscopic graphs illustrate that the bent-core molecules are able to self-assemble themselves into the Chinese character either in a sequential order or in a reverse order. Our results reveal that bent-core molecules have the capability of being smart materials.

Abstract: Infrared-induced alignment change with wavelength tunable CO2 laser irradiation for columnar liquid crystal domains was investigated for a triphenylene-based discotic liquid crystal. A uniformly aligned alignment change of domains was observed when a plused linearly polarized infrared laser light corresponding to the wavelength of the aromatic C-O-C stretching vibration band (9.65µm) was irradiated while it was not re-aligned uniformly with continious wave irradiation. The results strongly imply that the infrared irradiation is a possible technique for device fabrication by use of columnar mesophase as a liquid crystalline semiconductor.

Abstract: A rod-like liquid crystal 4-butoxybenzylidene-4'-octylphenylamine was synthesized. The molecular structure and the liquid crystalline phases of the synthesized compound were characterized with the nuclear magnetic resonance spectroscopy, the differential scanning calorimetry, and the polarizing optical microscopy, respectively. The absorption measurement shows that the dilute tetrahydrofuran solutions of the rod-like liquid crystal absorb photons at about 290 and 330 nm, respectively; while the luminescence measurements indicate that this rod-like liquid crystal can give off intense blue photoluminescence with its dominant peak located at about 430 nm. Using Hückel tight-binding program, we have calculated the electronic structures of the liquid crystal, and the origin of the blue photoluminescence is discussed. Introduction