A new series of liquid crystalline dimers with exceptionally high apparent tilt
| Autor: | Nils Olsson, Gunnar Andersson, Bertil Helgee, Martin W. Schröder, Lachezar Komitov, Siegmar Diele, Ingolf Dahl |
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| Rok vydání: | 2007 |
| Předmět: | |
| Zdroj: | J. Mater. Chem.. 17:2517-2525 |
| ISSN: | 1364-5501 0959-9428 |
| DOI: | 10.1039/b615541c |
| Popis: | A new series of dimeric chiral antiferroelectric materials using a trisiloxane as the central connecting linker and having fluorinated tails has been synthesized together with their corresponding monomers. Spacer lengths of 3–6 and 11 methylene groups were used. As a comparison to see the effect of the siloxane length on the phase behaviour, one dimer with a tetrasiloxane core was also synthesized. Monomers with 3–6 carbons in the spacer showed just orthogonal smectic phases and only the long 11 carbon spacer 7F4PPB11 showed tilted phases in a very similar way to what was found in the unfluorinated monomers previously studied. All trisiloxanes showed a high temperature antiferroelectric phase and those with a spacer length of 4 or more carbons also showed one or two columnar antiferroelectric phases when decreasing the temperature. The spontaneous polarisation Ps was high, especially in the columnar phases where it ranged from 800–1200 nC cm–2 and upward. The apparent tilt angles were exceptionally high, above 45 degrees for all materials studied. In accordance with the trend described previously, the tetrasiloxane containing dimer showed a ferroelectric phase at high temperature. But in this case the columnar phase was found to be antiferroelectric. Hence, the general idea that trisiloxane cores promote antiferroelectricity and tetrasiloxanes promote the ferroelectric phase is still correct also for these materials in the SmC* phase, but not for the columnar phase. It can also be noted that the phase separation between siloxane, fluorinated tail and mesogenic parts of the molecules was so high that the material became columnar on lowering the temperature. |
| Databáze: | OpenAIRE |
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