Liquid crystals and soft matter

Phase transitions & collective phenomena in liquid crystals

Giesselmann group

Formation of a nematic liquid crystal
Formation of a nematic liquid crystal in a first order phase transition on cooling from the isotropic melt, seen in the polarizing microscope. Due to its optical anisotropy the nematic phase appears bright, whereas the isotropic melt appears black.
Dielectric absorption spectrum of a ferroelectric liquid crystal
Dielectric absorption spectrum of a de Vries-type ferroelectric liquid crystal. The second order ferroelectric phase transition is signified by strong soft mode fluctuations. [M. Krueger et al., Phys. Rev. E 71, 041704 (2007).]
Formation of ferroelectric domains and zig-zag defects in a higher ordered smectic phase
Formation of ferroelectric domains and zig-zag defects in a higher ordered smectic phase of the chiral liquid crystal (+)-(4-(2'-methylbutyl)phenyl-4'-n-octylbiphenyl-4-carboxylate). [A. Saipa et al., Liquid Crystals 29, 347 (2002).]

Phase transitions & collective phenomena in liquid crystals

Phase transitions – the physical transformations between the various states of matter – are among the most remarkable examples of collective phenomena in nature. They are signified by abrupt changes in certain macroscopic properties, the origin of which is intimately connected to issues of symmetry, dimensionality as well as the range and symmetry of intermolecular interactions. Due to their soft nature with intermolecular interaction energies comparable to the thermal energy, liquid crystals exhibit a plethora of continuous or weakly first order phase transitions, making liquid crystals a perfect matter for the experimental and theoretical study of phase transitions.

We are mainly interested in phase transitions between smectic liquid crystal phases, in particular ferroelectric smectics. The transitions are experimentally studied (e.g., by X-ray diffraction, dielectric spectroscopy, Raman spectroscopy, and certain optic and electro-optic experiments) and analyzed in close collaboration with theory groups by phenomenological as well as molecular theories. In an international research effort with partners in the USA, Canada, Sweden and the UK, our group substantially contributed to the microscopic understanding of the mysterious “de Vries-type” phase transition in smectics, where the smectic layer thickness remains practically unchanged despite the tilting transition from the smectic A into the smectic C phase. The recognition of the molecular mechanisms behind this transition now led to the rational chemical design of new de Vries-type smectics, materials which are most important to avoid certain defects in ferroelectric liquid crystal display (FLCD) devices.

Selected Publications

Orientational fluctuations near the smectic A to smectic C phase transition in two “de Vries”-type liquid crystals
D. Nonnenmacher, S. Jagiella,Q. X. Song, R. P. Lemieux, F. Giesselmann, ChemPhysChem 14, 2990-2995 (2013).
DOI: 10.1002/cphc.201300358

Design of Liquid Crystals with "de Vries-like" Properties: Frustration between SmA- and SmC-Promoting Elements
J. C. Roberts, N. Kapernaum, Q. Song, D. Nonnenmacher, K. Ayub, F. Giesselmann, R. P. Lemieux, Journal of the American Chemical Society 132, 364-370 (2010).

Order-disorder molecular model of the smectic-A–smectic-C phase transition in materials with conventional and anomalously weak layer contraction
M. V. Gorkunov, M. A. Osipov, J. P. F. Lagerwall, F. Giesselmann, Physical Review E 76, 051706 (2007).
DOI: 10.1103/PhysRevE.76.051706

Current topics in smectic liquid crystals
J. P. F. Lagerwall, F. Giesselmann, ChemPhysChem 7, 20-45 (2006). DOI: 10.1002/cphc.200500472

Dielectric spectroscopy of 'de Vries' type smectic A* – C* transitions
M. Krueger, F. Giesselmann, Physical Review E 71, 041704 (2005).
DOI: 10.1103/PhysRevE.71.041704

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, M. D. Radcliffe, Physical Review E 66, 031703 (2002). DOI: 10.1103/PhysRevE.66.031703

Mean-field coefficients and electroclinic effect of a ferroelectric liquid crystal
F. Giesselmann, P. Zugenmaier, Physical Review E 52, 1762 (1995).
DOI: 10.1103/PhysRevE.52.1762

 

This picture showsFrank Gießelmann
Prof. Dr.

Frank Gießelmann

Professor

This picture showsNadia Kapernaum
Dr.

Nadia Kapernaum

Senior Scientist

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