The surface-mediated alignment control of a lyotropic liquid crystal (LLC) of aqueous solutions of a water-soluble dye, C. I. Direct blue 67, by using thin films of poly(4-phenylazophenyl methacrylate) as a command surface is described. Concentrated aqueous solutions of the dye in the presence of a non-ionic surfactant displayed mesophases as a chromonic LLC as a result of stacking of the aromatic ring systems leading to a columnar structure. A uniaxially oriented texture of LLC was obtained when the LLC, in the presence of a non-ionic surfactant was filled in a cell, which had been exposed in advance to linearly polarised light and was surface-modified with thin films of the polymer. The orientational direction of the dye molecules was in parallel with the electric vector of the actinic light, implying that the alignment of LLC is determined by perpendicularly photooriented azobenzene chromophores in such a way that columnar supramolecular aggregates of the dye align in parallel with the azobenzene molecular axis. Factors affecting the photoalignment control of the LLC were discussed on the basis of the results of the effects of exposure doses, excitation wavelength and photo-rewritability.
The in situ observation of thermal alteration of photoinduced optical anisotropy of ultrathin films of polymethacrylates having p-cyanoazobenzene side chains exhibiting amorphous, crystalline, and liquid-crystalline phases was performed by means of temperature scanning ellipsometry. Whereas photogenerated optical anisotropy of amorphous polymer films disappeared above glass transition temperature, the photoinduced anisotropy of films of liquid crystalline and crystalline polymer films was significantly amplified by heat treatment. In case of crystalline polymers, amplified optical anisotropy was maintained even at 300 °C.
Highly ordered liquid crystalline semiconductors on a light induced alignment layer results in an anisotropic electrical characteristic and an enhanced mobility of solution processed thin-film transistors. In the case of poly-9,9′-dioctyl-fluorene-co-bithiophene, a mobility as high as 0.02cm2V−1s−1 has been achieved by aligning a polymer chain parallel to the charge transport direction. Using an oligomeric semiconductor, 5,5′-bis(4-octyloxyphenyl)bithiophene, an enhanced mobility of 0.05cm2V−1s−1 was obtained by the alignment of the π-π intermolecular packing direction parallel to the charge transport direction.
Line up! Aligned single‐walled carbon nanotube (SWNT) films are formed from a lyotropic liquid‐crystalline high‐concentration SWNT/polymer composite (≈2 mg mL−1) dispersion. Birefringence from cross‐polarized microscopy is demonstrated as a uniaxial alignment of SWNTs (see images).
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