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A new series of liquid crystalline dimers with exceptionally high apparent tilt.

Författare och institution:
Nils Olsson (Institutionen för fysik (GU)); Martin Scroeder (-); Siegmar Diele (-); Gunnar Andersson (-); Ingolf Dahl (Institutionen för fysik (GU)); Bertil Helgee (Institutionen för fysik (GU)); Lachezar Komitov (Institutionen för fysik (GU))
Publicerad i:
Journal of Materials Chemistry, 17 ( 24 ) s. 2517-2525
Artikel, refereegranskad vetenskaplig
Sammanfattning (abstract):
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/cm2 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.
Ämne (baseras på Högskoleverkets indelning av forskningsämnen):
Fysik ->
Den kondenserade materiens fysik ->
Mesoskopisk fysik
Kemi ->
Organisk kemi ->
Organisk syntes
Elektroteknik och elektronik ->
Telekommunikation ->
Materialteknik ->
Annan materialteknik ->
Funktionella material
liquid crystals, dimer, chiral antiferroelectric, siloxane, tilt
Postens nummer:
Posten skapad:
2007-10-05 14:11
Posten ändrad:
2012-01-26 11:20

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