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Pettau, Robin ; Müller, Thomas ; Khazimullin, Maxim ; Rehberg, Ingo ; Schmidt, Hans-Werner:
Structure-property relations of liquid crystalline gels with ABA-triblock copolymers as gelators.
In: Zeitschrift für Physikalische Chemie : International Journal of Research in Physical Chemistry and Chemical Physics.
Bd. 226
(2012)
Heft 7-8
.
- S. 645-664.
ISSN 0942-9352
DOI: https://doi.org/10.1524/zpch.2012.0284
Angaben zu Projekten
| Projektfinanzierung: |
Deutsche Forschungsgemeinschaft Bayerisches Staatsministerium für Wissenschaft, Forschung und Kunst |
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Abstract
This paper reports on the influence of the structure of tailored ABA-triblock copolymers on physical gelation of the nematic liquid crystal 4'-n-pentyl-4-cyanobiphenyl (5CB), rheological properties, and the electro-optical response of the gels. The block copolymer gelators, comprised of two polystyrene A-blocks connected to a cyanobiphenyl-functionalized polyhydroxystyrene B-block, were synthesized by living anionic polymerization and functionalized by polymer analogous reactions. These block copolymers feature selective solubility. The B-block is soluble in the nematic and isotropic state of 5CB, whereas the polystyrene A-blocks are only soluble in the isotropic state. Consequently, upon cooling liquid crystalline gels are formed due to the controlled microphase-separation of the A-blocks. We show that the polymer composition and the different block lengths are important to vary the gel properties and the electro-optical response. It is confirmed that the gel formation correlates to the isotropic to nematic transition of 5CB for block copolymer gelators with sufficiently long A-blocks. Higher gel elasticity is obtained if gelators with short B-blocks are employed. The influence of the polymer network on the switching behavior of these liquid crystalline gels is investigated with respect to the electro-optical response in light scattering experiments. Intriguingly, these indicate a rearrangement of the nodes formed by the A-blocks under a strong electric field for block copolymers with short A-blocks.