- Photoorientation in hydrogen-bonded blends of liquid-crystalline polymers with a low-molecular photochromic dopant
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A series of hydrogen-bonded blends of nematic liquid-crystalline copolymers with a low-molecular photochromic dopant and their covalent analogs were prepared. Their phase behavior and photooptical properties were studied. The introduction of a dopant increases considerably the isotropization temperatures of the systems. A comparative study of photoorientation processes in the blends and copolymers analogous to them was carried out. The induced dichroism in covalent systems is more pronounced than in similar hydrogen-bonded blends.
- Obraztsov,Bobrovsky,Shibaev
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experimental part
p. 330 - 336
(2009/06/05)
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- Optical properties of side-chain liquid crystal copolymers of monosubstituted cholesteryl itaconate and a non-chiral mesogen
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New mono- and disubstituted cholesteryl derivatives of itaconic acid have been prepared and their thermotropic liquid crystalline behaviour examined.The monosubstituted derivative has been homopolymerized, and also copolymerized with a non-chiral mesogen 4-cyanophenyl-4'-(6-acryloyloxyhexyloxy) benzoate.Examination of the series of copolymers prepared, using differential scanning calorimetry and hot-stage polarizing microscopy, showed that when the content of the cholesteryl itaconate was high, both a smectic-A phase (SA) and a cholesteric phase (N*) were present.It was found that the SA phase could be eliminated by lowering the content of the cholesteryl itaconate in the copolymers, giving samples that displayed only the N* phase over a much wider temperature range.The samples in the N* phase also exhibited selective reflection of visible light that changed from short to long wavelengths as the samples were cooled from the isotropic melt.These colours can be locked into the glassy state of the polymer by quenching below the glass transition temperature, but only if the SA phase is absent.It was also noted that at high contents of the cholesteryl itaconate the selective reflection appears to occur in the ultraviolet region. - Keywords: itaconic acid; copolymers; liquid crystalline polymers; cholesteric phases; selective reflection
- Cowie, J. M. G.,Hunter, H. W.
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p. 1811 - 1817
(2007/10/03)
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