Open Access. Powered by Scholars. Published by Universities.®

Physics Commons

Open Access. Powered by Scholars. Published by Universities.®

Articles 1 - 10 of 10

Full-Text Articles in Physics

Pattern-Stabilized Decorated Polar Liquid-Crystal Fibers, Alexey Eremin, Ulrike Kornek, Stephan Stern, Ralf Stannarius, Fumito Araoka, Hideo Takezoe, Hajnalka Nadasi, Wolfgang Weissflog, Antal Jakli Jul 2012

Pattern-Stabilized Decorated Polar Liquid-Crystal Fibers, Alexey Eremin, Ulrike Kornek, Stephan Stern, Ralf Stannarius, Fumito Araoka, Hideo Takezoe, Hajnalka Nadasi, Wolfgang Weissflog, Antal Jakli

Chemical Physics Publications

Geometric frustration gives rise to new fundamental phenomena and is known to yield the formation of exotic states of matter, such as incommensurate crystals, modulated liquid-crystalline phases, and phases stabilized by defects. In this Letter, we present a detailed study of polar structure of freely suspended fluid filaments in a polarization modulated liquid-crystal phase. We show that a periodic pattern of polarization-splay stripes separated by defect boundaries and decorating smectic layers can stabilize the structure of fluid fibers against the Rayleigh-Plateau instability. The instability is suppressed by the resistance of the defect structure to a radial compression of the cylindrical ...


Homogeneous And Homeotropic Alignment Of Bent-Core Uniaxial And Biaxial Nematic Liquid Crystals, Hyungguen Yoon, Shin-Woong Kang, Matthias Lehmann, Jung Ok Park, Mohan Srinivasarao, Satyendra Kumar Jan 2011

Homogeneous And Homeotropic Alignment Of Bent-Core Uniaxial And Biaxial Nematic Liquid Crystals, Hyungguen Yoon, Shin-Woong Kang, Matthias Lehmann, Jung Ok Park, Mohan Srinivasarao, Satyendra Kumar

Physics Publications

The effect of well-established homeotropically and homogeneously aligning polyimides, developed for calamitic liquid crystals, on the alignment of the nematic phases of bent-core mesogens was investigated using polarizing optical microscopy and conoscopy. Two polyimides, the homogeneously aligning SE7792 and the homeotropically aligning S659, were used to align three bent-core mesogens. Two of the mesogens, with an azo group in one of their arms, are found to align in a manner similar to the calamitic mesogens, while a fluorenone core based mesogen counter-intuitively aligns homogeneously on S659 coated surface and homeotropically on SE7792. Attractive interactions between unidirectionally oriented polyimide side-chains and ...


Bundles Of Fluid Fibers Formed By Bent-Core Molecules, C. Bailey, M. Murphy, A. Eremin, Wolfgang Weissflog, Antal Jakli Mar 2010

Bundles Of Fluid Fibers Formed By Bent-Core Molecules, C. Bailey, M. Murphy, A. Eremin, Wolfgang Weissflog, Antal Jakli

Chemical Physics Publications

The internal structures, stability, and elastic properties of free-standing filament bundles of bent-core smectic liquid crystals are studied using polarizing microscopy, scanning electron microscopy, and a customized cantilever containing, temperature controlled heat stage for force measurements. We find that in bundles, the individual filaments fuse together to form semiseparable filaments with radii approximately two and three times larger than the individual fibers. We also find that the effective surface tension of wide bundles is about 10% smaller than a single filament. Finally, we describe the metastable coexistences of single fibers within the bundles that lead to bending of the bundles ...


Photo-Responsive And Electrically Switchable Mesophases In A Novel Class Of Achiral Bent-Core Azo Compounds, Veena Prasad, Shin-Woong Kang, Xianghong Qi, Satyendra Kumar May 2004

Photo-Responsive And Electrically Switchable Mesophases In A Novel Class Of Achiral Bent-Core Azo Compounds, Veena Prasad, Shin-Woong Kang, Xianghong Qi, Satyendra Kumar

Physics Publications

The first examples of electrically switchable and photo-responsive mesophases in a novel class of bent-core azo compounds, consisting of only five aromatic rings and no imino functionality (-CH=N-), are reported. The rnesophases have been identified as B-1, B-2 and a new mesophase, B-x on the basis of the results of polarizing optical microscopy, differential scanning calorimetry, X-ray diffraction, and electro-optical response. Preliminary but profound photo-induced effects on the transition temperature from isotropic to the B, mesophase of one of the azo compounds are also presented.


Nanophase Segregation Of Nonpolar Solvents In Smectic Liquid Crystals Of Bent-Shape Molecules, M.Y.M. Huang, A.M. Pedreira, O.G. Martins, A.M.F. Neto, Antal Jakli Sep 2002

Nanophase Segregation Of Nonpolar Solvents In Smectic Liquid Crystals Of Bent-Shape Molecules, M.Y.M. Huang, A.M. Pedreira, O.G. Martins, A.M.F. Neto, Antal Jakli

Chemical Physics Publications

Electro-optical, calorimetric, x-ray, and dielectric measurements are reported on a mixture containing a bent-core liquid crystal 4-chloro-1,3-phenylinebis [4-(4-n-tetradecyloxyphenyliminomethyl) benzoate] mixed with the nonpolar solvent n-hexadecane (HEX). It is observed that the addition of HEX depresses the isotropic-to-smectic phase transition temperature, but the crystallization temperature does not change considerably. Instead, the texture of the crystalline phase changes and, at sufficiently high concentrations of HEX (>20 wt %), an optically isotropic phase appears. Above 40 wt % HEX concentrations, the mesophase completely disappears and a direct isotropic solid-to-isotropic liquid transition takes place. At increasing HEX concentration, the transition enthalpies, the layer ordering ...


Surface States In Nearly Modulated Systems, A. E. Jacobs, D. Mukamel, David W. Allender Feb 2001

Surface States In Nearly Modulated Systems, A. E. Jacobs, D. Mukamel, David W. Allender

Physics Publications

A Landau model is used to study the phase behavior of the surface layer for magnetic and cholesteric liquid-crystal systems that are at or near a Lifshitz point marking the boundary between modulated and homogeneous bulk phases. The model incorporates surface and bulk fields and includes a term in the free energy proportional to the square of the second derivative of the order parameter in addition to the usual term involving the square of the first derivative. In the limit of vanishing bulk field, three distinct types of surface ordering are possible: a wetting layer, a nonwet layer having a ...


Deuteron Nmr Investigation Of A Photomechanical Effect In A Smectic-A Liquid Crystal, Boštjan Zalar, Oleg Lavrentovich, Huairen Zeng, Daniele Finotello Aug 2000

Deuteron Nmr Investigation Of A Photomechanical Effect In A Smectic-A Liquid Crystal, Boštjan Zalar, Oleg Lavrentovich, Huairen Zeng, Daniele Finotello

Chemical Physics Publications

Deuteron quadrupole-perturbed NMR is used to study the perturbation of orientational order in a smectic-A liquid crystal (octylcyanobiphenyl or 8CB) caused by photoinduced trans-to-cis isomerization of a photosensitive dopant (diheptylazobenzene or 7AB). The time and temperature dependences of the orientational order were independently studied for 8CB, 7AB, and their mixtures. Upon UV irradiation that causes trans-to-cis isomerization of 7AB, the orientational order parameter of the smectic-A phase is reduced. Relaxation in the dark exponentially restores the equilibrium value of the order parameter. The characteristic time for this process closely matches the lifetimes of the 7AB excited state. While ...


Novel Surface State In A Class Of Incommensurate Systems, A. E. Jacobs, D. Mukamel, David W. Allender Mar 2000

Novel Surface State In A Class Of Incommensurate Systems, A. E. Jacobs, D. Mukamel, David W. Allender

Physics Publications

We study the Landau model of the class of incommensurate systems with a scalar order parameter where the modulated phase is driven by a gradient-squared term with negative coefficient. For example, theoretical studies of cholesteric liquid crystals in a field (electric or magnetic) suggest that such an modulated phase should exist at high chirality. The bulk phase diagram in the presence of a bulk external field which couples linearly to the order parameter exhibits a modulated phase inside a loop in the temperature-field plane, and a homogeneous phase outside. On analyzing the same model for a semi-infinite system, we find ...


Curvature Energy Of A Focal Conic Domain With Arbitrary Eccentricity, Maurice Kleman, Oleg Lavrentovich Feb 2000

Curvature Energy Of A Focal Conic Domain With Arbitrary Eccentricity, Maurice Kleman, Oleg Lavrentovich

Chemical Physics Publications

The most frequently observed focal conic domains (FCD’s) in lamellar phases are those based on confocal paris of ellipse and hyperbola. Experimentally, the eccentricity of the ellipse takes a broad range of values 0<~eeisolated FCD reaches a minimum only at e⃗1 (under the constraint of a fixed major semiaxis of the ellipse); exceptions include situations with large saddle-splay elastic constant and small domains where the applicability of the elastic theory is limited. In realistic cases, a value of eccentricity smaller than 1 is stabilized by factors other than the curvature energy: by dislocations emerging from the ...


Helical Single-Lamellar Crystals Thermotropically Formed In A Synthetic Nonracemic Chiral Main-Chain Polyester, Christopher Y. Li, Donghang Yan, Stephen Z. D. Cheng, Feng Bai, Jason J. Ge, Bret H. Calhoun, Tianbai He, Liang-Chy Chien, Frank W. Harris, Bernard Lotz Nov 1999

Helical Single-Lamellar Crystals Thermotropically Formed In A Synthetic Nonracemic Chiral Main-Chain Polyester, Christopher Y. Li, Donghang Yan, Stephen Z. D. Cheng, Feng Bai, Jason J. Ge, Bret H. Calhoun, Tianbai He, Liang-Chy Chien, Frank W. Harris, Bernard Lotz

Chemical Physics Publications

Phase structures and transformation mechanisms of nonracemic chiral biological and synthetic polymers are fundamentally important topics in understanding their macroscopic responses in different environments. It has been known for many years that helical structures and morphologies can exist in low-ordered chiral liquid crystalline (LC) phases. However, when the chiral liquid crystals form highly ordered smectic liquid crystal phases, the helical morphology is suppressed due to the crystallization process. A double-twisted morphology has been observed in many liquid crystalline biopolymers such as dinoflaggellate chromosomes (in Prorocentrum micans) in an in vivo arrangement. Helical crystals grown from solution have been reported in ...