General Mesophases
by H. Pleiner
(external collaboration with P.K. Mukherjee and H.R. Brand)
First, smectic liquid crystals are investigated. They serve as model systems for micellar lamellar and ordered diblock copolymer phases and they are used for display applications. Their nonlinear behaviour as well as their electro-optic properties are of special interest [A]. Nonlinear dynamic equations (including external fields) for tilted smectic C phases are derived. Direct phase transitions from the isotropic to various smectic phases are discussed [B].
As an example, a direct isotropic to smectic A phase transition is shown (in red) that precedes the isotropic to nematic transition (in blue) for a negative crosscoupling between the nematic(S) and the smectic order parameter (ψ0) in the free energy.
Second, cholesteric liquid crystals are investigated. Although not really layered phases, their large-scale behavior is rather similar to that of smectics. Flow properties, thermo- and electromechanical couplings are prominent features on the global as well as on the local scale [C]. Generalized static as well as dynamic Lehmann-type effects are considered (cf. also Membranes, Films and Surface Waves). Symmetry and relaxing variables are discussed for the sponge (L3) phase [D].
Recently, the macroscopic dynamics of a homogeneous polar nematic phase has been derived [E] (for a polar nematic splay phase, cf. H. Pleiner and H.R. Brand, Europhys. Lett. 9, 243 (1989)).
Recent Publications:
H. Pleiner and H.R. Brand, "Piezoelectricity in cholesteric liquid crystalline structures", [C]
J. Phys. II (France) 3,
1397 (1993), [392 kB pdf-file] and
Proceedings Freiburger Arbeitstagung Flüssigkristalle 22, 22 (1993) [80 kB pdf-file]
- polar versus non-polar cholesteric phases
H. Pleiner and H.R. Brand, "Dielectric Degrees of Freedom in Chiral Smectic C Liquid Crystals", [A]
Mol. Cryst. Liq. Cryst. 257, 289 (1994) [86 kB pdf-file]
H.R. Brand and H. Pleiner, "Comment on 'Coupling between Elastic Deformation and Concentration in a Two-Component Nematic Liquid Crystal'",
Europhys. Lett. 26,
395 (1994) [68 kB pdf-file]
H.R. Brand and H. Pleiner, "Flexoelectric effects in cholesteric liquid crystals", [C]
Mol. Cryst. Liq. Cryst. 292,
141 (1997), [336 kB pdf-file]
H. Pleiner and H.R. Brand, "Nonlinear Hydrodynamics of strongly deformed smectic C and C* Liquid Crystals", [A]
Ferroelectrics 214, 19 (1998) , [588 kB pdf-file] and
Physica A 265 , 62 (1999), [627 kB pdf-file]
H. Pleiner, P.K. Mukherjee, and H.R. Brand, "Direct transitions from isotropic to smectic phases", [B]
Proceedings Freiburger Arbeitstagung Flüssigkristalle 29 , P59 (2000), [689 kB pdf-file]
P.K. Mukherjee, H. Pleiner, and H.R. Brand, "Simple Landau Model of the Smectic A - Isotropic Phase Transition", [B]
Eur. Phys. J. E 4, 293 (2001), [928 kB pdf-file]
H.R. Brand and H. Pleiner, "Cholesteric Liquid Crystals: Flow Properties, Thermo- and Electromechanical Coupling", [C]
Encyclopedia of Materials: Science and Technology, Elsevier, Vol.5, pp. 1214-1219 (2001),
[1.4 MB pdf-file]
            update (addendum) in 2015: "Recent Developments", [433 kB pdf-file]; whole article now in
Reference Module in Materials Science and Materials Engineering, Science Direct, Elsevier, DOI: 10.1016/B978-0-12-803581-8.02753-3
H.R. Brand, P.K. Mukherjee, and H. Pleiner, "Macroscopic Dynamics near the Isotropic - Smectic A Phase Transition", [B]
Phys. Rev. E 63, 061708 (2001), [604 kB pdf-file] DOI: 10.1103/PhysRevE.63.061708
H. Pleiner and H.R. Brand, "Incompressibility Conditions in Liquid
Crystals"
Continuum Mech.Thermodyn. 14, 297 (2002), [654 kB pdf-file] DOI: 10.1007/s00161-001-0098-9
H.R. Brand and H. Pleiner, "Transient orientational order and transient positional order in the sponge
(L3) phase", [D]
Physica A 312, 79 (2002), [408 pdf-file] DOI: 10.1016/S0378-4371(02)00870-1
P.K. Mukherjee, H. Pleiner, and H.R. Brand, "Landau Model of the Smectic C - Isotropic Phase Transition", [B]
J. Chem. Phys. 117, 7788 (2002), [183 kB pdf-file] DOI: 10.1063/1.1509055
P.K. Mukherjee, H. Pleiner, and H.R. Brand, "A phenomenological theory of the isotropic to chiral smectic C phase transition", [B]
Eur. Phys. J. E 17, 501 (2005), [148 kB pdf-file] DOI: 10.1140/epje/i2004-10153-6
H.R. Brand, H. Pleiner, and F. Ziebert, "Macroscopic dynamics of polar nematic liquid crystals", [E]
Phys. Rev. E 74, 021713 (2006), [163 kB pdf-file] DOI: 10.1103/PhysRevE.74.021713
D. Svenek, H. Pleiner, and H.R. Brand, "Inverse Lehmann effect can be used as a microscopic pump",
Phys. Rev. E 78, 021703 (2008), [121 kB pdf-file] DOI: 10.1103/PhysRevE.78.021703
H. Pleiner and H.R. Brand, "Comment on 'Direct measurements of the thermomechanical
Lehmann coefficient in a compensated cholesteric liquid crystal' by Oswald P. and Dequidt A."
Europhys. Lett. 89, 26003 (2010), [278 kB pdf-file] DOI: 10.1209/0295-5075/89/26003
H.R. Brand, H. Pleiner, and D. Svenek, "Macroscopic behavior of systems with an axial dynamic preferred direction",
Eur. Phys. J. E 34, 128 (2011), [262 kB pdf-file] DOI: 10.1140/epje/i2011-11128-2
H.R. Brand, H. Pleiner, and D. Svenek, "Lehmann effects and rotato-electricity in liquid crystalline systems made of achiral molecules",
Phys. Rev. E 88, 024501 (2013), [243 kB pdf-file] DOI: 10.1103/PhysRevE.88.024501
H.R. Brand and H. Pleiner, "Cubic and tetragonal liquid crystal phases
composed of non-chiral molecules: Chirality and macroscopic properties",
Eur. Phys. J. E 42, 142 (2019), [287 kB pdf-file] DOI: 10.1140/epje/i2019-11906-8
H.R. Brand and H. Pleiner, "Macroscopic behavior of the distorted A and B phases and the polar phase
of superfluid 3He in an anisotropic aerogel",
Phys. Rev. B 102, 094510 (2020), [369 kB pdf-file] DOI: 10.1103/PhysRevB.102.094512
H.R. Brand and H. Pleiner, "Macroscopic behavior of the P_1 (β) and P_2 (distorted β) phases of superfluid 3He: Sound-like excitations",
Phys. Rev. B 105, 174508 (2022), [300 kB pdf-file] DOI: 10.1103/PhysRevB.105.174508
preprints of the theory group
Other research topics:
Instabilities in Complex Fluids
Rheology of Complex Fluids
Non-magnetic Liquid Crystalline Polymers and Elastomers
Membranes, Films and Surface Waves
Banana and Dolphin Phases
Magnetic Fluids and Elastomers
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HARALD PLEINER
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