Liquid‐crystalline side group polyesters with definite lengths of flexible spacers in the main chain

Böhme, Axel; Novotná, Eva; Kresse, H.; Kuschel, Frank; Lindau, J.

doi:10.1002/macp.1993.021941212

Cited by 23 publications

(13 citation statements)

References 13 publications

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“…ii tr n tr + σ (cis) n cis ∝ (1 + u (a) (2 S i + 1)/3)n tr + q ct n cis , (32) where S i ≡ S ii tr ; u (a) is the absorption anisotropy parameter and q ct is the ratio of σ (cis) and σ (tr) ⊥ at the wavelength of probing light.…”

Section: Numerical Resultsmentioning

confidence: 99%

Photoinduced three-dimensional orientational order in side chain liquid crystalline azopolymers

et al. 2003

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We apply experimental technique based on the combination of methods dealing with principal refractive indices and absorption coefficients to study the photoinduced 3D orientational order in the films of liquid crystalline (LC) azopolymers. The technique is used to identify 3D orientational configurations of trans azobenzene chromophores and to characterize the degree of ordering in terms of order parameters. We study two types of LC azopolymers which form structures with preferred in-plane and out-of-plane alignment of azochromophores, correspondingly. Using irradiation with the polarized light of two different wavelengths we find that the kinetics of photoinduced anisotropy can be dominated by either photo-reorientation (angular redistribution of trans chromophores) or photoselection (angular selective trans-cis isomerization) mechanisms depending on the wavelength. At early stages of irradiation the films of both azopolymers are biaxial. This biaxiality disappears on reaching a state of photo-saturation. In the regime of photoselection the photo-saturated state of the film is optically isotropic. But, in the case of the photo-reorientation mechanism, anisotropy of this state is uniaxial with the optical axis dependent on the preferential alignment of azochromophores. We formulate the phenomenological model describing the kinetics of photoinduced anisotropy in terms of the isomer concentrations and the order parameter tensor. We present the numerical results for absorption coefficients that are found to be in good agreement with the experimental data. The model is also used to interpret the effect of changing the mechanism with the wavelength of the pumping light.

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Section: Numerical Resultsmentioning

confidence: 99%

Photoinduced three-dimensional orientational order in side chain liquid crystalline azopolymers

et al. 2003

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“…1) as model polymer whose synthesis is described in [25]. The thermal properties of the polymer are characterized by the transition temperatures C 1 -32 • -C 2 -44 • -S 52 • -N-55 • -I detected by DSC and polarizing microscopy of the polymer in the bulk.…”

Section: Samples Preparation and Irradiation Proceduresmentioning

confidence: 99%

Spatial reorientation of azobenzene side groups of a liquid crystalline polymer induced by linearly polarized light

Yaroshchuk

Kiselev

Zakrevskyy

et al. 2001

The European Physical Journal E

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The photoinduced 3D orientational structures in films of a liquid crystalline polyester, containing azobenzene side groups, are studied both experimentally and theoretically. By using the null ellipsometry and the UV/Vis absorption spectroscopy, the preferential in-plane alignment of the azobenzene fragments and in-plane reorientation under irradiation with linearly polarized UV light are established. The uniaxial and biaxial orientational order of the azobenzene chromophores are detected. The biaxiality is observed in the intermediate stages of irradiation, whereas the uniaxial structure is maintained in the photosaturated state of the photo-orientation process. The components of the order parameter tensor of the azobenzene fragments are estimated for the initial state and after different doses of irradiation. The proposed theory takes into account biaxiality of the induced structures. Numerical analysis of the master equations for the order parameter tensor is found to yield the results that are in good agreement with the experimental dependencies of the order parameter components on the illumination time

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“…The mesomorphic behavior of substances was investigated by polarizing microscopy (Nikon Labophot 2A, hot stage: THMS 600 from Linkam) and differential scanning calorimetry (Perkin-Elmer-DSC 7). In all cases the heating and cooling rates were 10 Wmin unless otherwise specified.…”

Section: Methods Of Characterizationmentioning

confidence: 99%

Thermal phase behavior of homologous liquid crystalline side group polyesters in dependence on the polymethylene main chain spacer length

Emmerling

Diele

Schmalfuss

et al. 1998

Macromol. Chem. Phys.

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SUMMARY With the aim to investigate the influence of a systematic variation of the length of flexible nonmesogenic main chain segments on the mesomorphic properties a series of new liquid crystalline polyesters with 4-(4-nitrobenzyloxy)biphenyl moieties as mesogenic side groups was prepared. The mesomorphic and dynamic behavior were investigated by means of differential scanning calorimetry (DSC), X-ray measurements, polarization microscopy and dielectric spectroscopy. All polyesters exhibit nematic and different smectic phases. Some of the homologues show "re-entrant" nematic phases. The clearing point decreases at first with increasing main chain spacer length and passes through a minimum. From the results it was possible to propose packing models of the smectic phases with low order.

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Liquid‐crystalline side group polyesters with definite lengths of flexible spacers in the main chain

Cited by 23 publications

References 13 publications

Photoinduced three-dimensional orientational order in side chain liquid crystalline azopolymers

Photoinduced three-dimensional orientational order in side chain liquid crystalline azopolymers

Spatial reorientation of azobenzene side groups of a liquid crystalline polymer induced by linearly polarized light

Thermal phase behavior of homologous liquid crystalline side group polyesters in dependence on the polymethylene main chain spacer length

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