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Chemical Physics Publications

Mesogens

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Full-Text Articles in Physics

Surface Alignment, Anchoring Transitions, Optical Properties, And Topological Defects In The Nematic Phase Of Thermotropic Bent-Core Liquid Crystal A131, B. Senyuk, H. Wonderly, M. Mathews, Q. Li, Sergij V. Shiyanovskii, Oleg Lavrentovich Oct 2010

Surface Alignment, Anchoring Transitions, Optical Properties, And Topological Defects In The Nematic Phase Of Thermotropic Bent-Core Liquid Crystal A131, B. Senyuk, H. Wonderly, M. Mathews, Q. Li, Sergij V. Shiyanovskii, Oleg Lavrentovich

Chemical Physics Publications

We study optical, structural, and surface anchoring properties of thermotropic nematic bent-core material A131. The focus is on the features associated with orientational order as the material has been reported to exhibit not only the usual uniaxial nematic but also the biaxial nematic phase. We demonstrate that A131 experiences a surface anchoring transition from a perpendicular to tilted alignment when the temperature decreases. The features of the tilted state are consistent with surface-induced birefringence associated with smectic layering near the surface and a molecular tilt that changes along the normal to the substrates. The surface-induced birefringence is reduced to zero ...


Short-Range Smectic Order In Bent-Core Nematic Liquid Crystals, Seung Ho Hong, Rafael Verduzco, J. C. Williams, Robert J. Twieg, E. Dimasi, R. Pindak, Antal Jakli, Jim T. Gleeson, Samuel N. Sprunt Aug 2010

Short-Range Smectic Order In Bent-Core Nematic Liquid Crystals, Seung Ho Hong, Rafael Verduzco, J. C. Williams, Robert J. Twieg, E. Dimasi, R. Pindak, Antal Jakli, Jim T. Gleeson, Samuel N. Sprunt

Chemical Physics Publications

Small angle X-ray diffraction from the uniaxial nematic phase of certain bent-core liquid crystals is shown to be consistent with the presence of molecular clusters possessing short-range tilted smectic (smectic-C) order. Persistence of these clusters throughout the nematic phase, and even into the isotropic state, likely accounts for the unusual macroscopic behavior previously reported in bent-core nematics, including an anomalously large flexoelectric effect (similar to 1000 times that of conventional calamitic nematics), very large orientational and flow viscosities (similar to 10 100 and similar to 100 1000 times, respectively, typical values for calamitics), and an extraordinary flow birefringence observed in ...


Large Flow Birefringence Of Nematogenic Bent-Core Liquid Crystals, C. Bailey, Katalin Fodor-Csorba, Rafael Verduzco, Jim T. Gleeson, Samuel N. Sprunt, Antal Jakli Dec 2009

Large Flow Birefringence Of Nematogenic Bent-Core Liquid Crystals, C. Bailey, Katalin Fodor-Csorba, Rafael Verduzco, Jim T. Gleeson, Samuel N. Sprunt, Antal Jakli

Chemical Physics Publications

We have found that bent-core liquid crystalline materials show exceptionally large intrinsic flow birefringence in their isotropic liquid phase. This effect is more than 100 times larger than typical values measured for low molecular weight liquid crystals. The specific flow birefringence (i.e., normalized by the flow viscosity) is an order of magnitude larger than in both side-chain polymeric as well as low molecular weight liquid crystals. We propose that this large enhancement for bent-core compounds may be attributed to nanoscale smecticlike clusters that persist above the nematic-isotropic transition temperature, and shear align under shear flow; however, this mechanism has ...


Role Of Molecular Shape On Bent-Core Liquid-Crystal Structures, C. Bailey, Antal Jakli Nov 2007

Role Of Molecular Shape On Bent-Core Liquid-Crystal Structures, C. Bailey, Antal Jakli

Chemical Physics Publications

We show how frustrations in molecular packing generated by molecular substitutions and electrostatic potentials necessitate a local C(1) symmetry and lead to spontaneous polarization splay and layer bending in bent-core liquid crystals. By estimation of the entropic changes due to curvature, we calculated the elastic constants that drive the spontaneous layer bend and polarization splay and obtained length scales of these deformations. Finally, we propose a structural phase diagram which describes how the experimentally observed helical superstructures, layer undulation, polarization splay, and spontaneous fiber formation depend on the direction and magnitude of the spontaneous polarization.


Critical Behavior At The Isotropic-To-Nematic Phase Transition In A Bent-Core Liquid Crystal, D. B. Wiant, S. Stojadinovic, K. Neupane, S. Sharma, Katalin Fodor-Csorba, Antal Jakli, Jim T. Gleeson, Samuel N. Sprunt Mar 2006

Critical Behavior At The Isotropic-To-Nematic Phase Transition In A Bent-Core Liquid Crystal, D. B. Wiant, S. Stojadinovic, K. Neupane, S. Sharma, Katalin Fodor-Csorba, Antal Jakli, Jim T. Gleeson, Samuel N. Sprunt

Chemical Physics Publications

Magnetic birefringence and dynamic light scattering measurements of orientational order parameter fluctuations at the isotropic-nematic phase transition of a bent-core liquid crystal reveal a pretransitional temperature dependence consistent with the standard Landau-deGennes mean field theory. However, as follows: the transition in the bent-core compound is more weakly first order (T(NI)-T(*)approximate to 0.4 degrees C), the leading Landau coefficient is similar to 30 times lower, the viscosity associated with nematic order fluctuations is similar to 10 times higher, and the density change is similar to 10 times lower, than typically observed in calamitic (rod-shaped) liquid crystals. One ...


Antiferroelectric Ordering Of Amphiphilic Glycolipids In Bent-Core Liquid Crystals, Sugat Abeygunaratne, Antal Jakli, Gotz Milkereit, Hans Sawade, Volkmar Vill Feb 2004

Antiferroelectric Ordering Of Amphiphilic Glycolipids In Bent-Core Liquid Crystals, Sugat Abeygunaratne, Antal Jakli, Gotz Milkereit, Hans Sawade, Volkmar Vill

Chemical Physics Publications

Lipids are the main constituents of biological cell membranes, and their liquid crystalline properties play a crucial role in cell functions. We have discovered that dodecyl-beta-D-glucopyranoside glycolipid layers can be electrically polarized in supramolecular structures of glycolipid and bent-core ("banana-shape") molecules. Interestingly the glycolipid molecules, known to be excellent chiral dopants, are not able to transfer their chirality to the bent-core layers. Our observations indicate that glycolipid molecules self-assemble into pairs of tilted and antiferroelectric double layers, sandwiched between layers of bent-core molecules. These systems may provide a basis for understanding "bioferroelectricity," which is important in biological cell membrane functions.