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Funding
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DAAD 99/16457
und 313 A/01/09549 |
| Cooperation
with |
Dr. M. D. Radcliffe,
3M Corporation, Minnesota, USA
Prof. S. T. Lagerwall, Chalmers University of Technology,
Göteborg, Sweden
Prof. Dr. M. Glogarowa, Academy of Sciences, Prague,
Czech Republic
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| Description of
project |
The molecular
origin of the optical tilt observed in Sm-C liquid crystals has been an
issue of debate ever since the discovery in the early 1970s that a compound
exhibiting Sm-A and Sm-C phases generally has a temperature dependent tilt
angle. The last few years the question has received renewed interest due
to the recognition of its importance in the manufacturing of high-quality
electro-optic devices based on ferro- or antiferroelectric, i.e., chiral
Sm-C* or Sm-Ca*, liquid crystals (FLCs, AFLCs). The main obstacle in the
commercialization of such devices has turned out to be the problems related
to the shrinking of the smectic layers which occurs at the transition from
the orthogonal (director parallel to the layer normal ) Sm-A* phase to the
tilted Sm-C* (or Sm-Ca*) phase. As the layers are positionally anchored
at the surfaces, they will then buckle in a chevron geometry which is the
only one compatible with the new combination of surface and bulk conditions.
Accompanying the development of the chevron structure is the formation of
so-called 'zig-zag' defects and a reduction in effective optical tilt angle,
effects which seriously degrade the quality of any electro-optic device.
The exact connection between director tilting and layer thickness change
is however still not fully understood, and different materials show varying
degree of shrinkage as a result of the tilting transition. In fact, a number
of FLC materials displaying virtually constant smectic layer spacings have
been identified, and these materials ("de Vries materials") have therefore
come to receive a substantial interest from industry as well as academia.
An understanding of why such de Vries materials do not show a shrinkage
of the layers at the Sm-A* -- Sm-C* transition, and why others do, is not
only a key issue for the development of FLC and AFLC electro-optic devices,
but it is also extremely interesting from a fundamental research point of
view.
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| Publications |
Dielektrische Spektroskopie
ferroelektrischer Flüssigkristalle mit anomalem Verhalten der
smektischen Schichtdicke an Phasenübergängen
Diplomarbeit,
Michael Krueger (2004)
Ferroelectric polysiloxane liquid crystals with "de
Vries"-type smectic A* - smectic C* transitions
M. Rössle, R. Zentel, J. P. F. Lagerwall and
F. Giesselmann
Liquid Crystals 31(6), 883-887 (2004)
Smektische
Phasenumwandlungen in einer Reihe chiraler
ferroelektrischer Flüssigkristalle
Diplomarbeit, Samuel Bezner (2003)
Antiferroelectric
liquid-crystal mixture without smectic layer shrinkage at the direct Sm-A*
- Sm-C* transition
F. Giesselmann*, J. P. F. Lagerwall, G. Andersson and M. D. Radcliffe
Physical Review E 66, 051704 (2002)
Optical and x-ray evidence of the "de Vries" Sm-A* - SmC* transition
in a non-layer-shrinkage ferroelectric liquid crystal with very weak interlayer
tilt correlation
J. P. F. Lagerwall, F. Giesselmann*, and M. D. Radcliffe
Physical Review E 66, 031703 (2002)
Smectic-A* - smectic-C* transition in a ferroelectric liquid crystal
without smectic layer shrinkage
F. Giesselmann*, P. Zugenmaier, I. Dierking, S. T. Lagerwall, B. Stebler,
M. Kaspar, V. Hamplova, and M. Glogarova
Physical Review E 60(1), 598 - 602
(1999)
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Contact
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f.giesselmann... |
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Stuttgart | Impressum