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Full-Text Articles in Physics

Lyotropic Chromonic Liquid Crystal Semiconductors For Water-Solution Processable Organic Electronics, V. G. Nazarenko, O. P. Boiko, M. I. Anisimov, A. K. Kadashchuk, Yuriy A. Nastishin, A. B. Golovin, Oleg Lavrentovich Dec 2010

Lyotropic Chromonic Liquid Crystal Semiconductors For Water-Solution Processable Organic Electronics, V. G. Nazarenko, O. P. Boiko, M. I. Anisimov, A. K. Kadashchuk, Yuriy A. Nastishin, A. B. Golovin, Oleg Lavrentovich

Chemical Physics Publications

We propose lyotropic chromonic liquid crystals (LCLCs) as a distinct class of materials for organic electronics. In water, the chromonic molecules stack on top of each other into elongated aggregates that form orientationally ordered phases. The aligned aggregated structure is preserved when the material is deposited onto a substrate and dried. The dried LCLC films show a strongly anisotropic electric conductivity of semiconductor type. The field-effect carrier mobility measured along the molecular aggregates in unoptimized films of LCLC V20 is 0.03 cm(2) V-1 s(-1). Easy processibility, low cost, and high mobility demonstrate the potential of LCLCs for ...


Fabrication And Characterization Of Coupled Metal-Dielectric-Metal Nanoantennas, Bhuwan Joshi, Xuejin Wen, Kai Sun, Wu Lu, Qi-Huo Wei Nov 2010

Fabrication And Characterization Of Coupled Metal-Dielectric-Metal Nanoantennas, Bhuwan Joshi, Xuejin Wen, Kai Sun, Wu Lu, Qi-Huo Wei

Chemical Physics Publications

The authors fabricated two dimensional arrays of metal-dielectric-metal nanoantennas consisting of a thin layer of light-emitting polymers sandwiched between two Ag parallel cuboids and characterized them by measuring the optical transmission through the antenna arrays. The measured transmission spectra show two resonant dips. Numerical simulations reproduce the experimental results and show that the left dip is due to a cavity resonance mode and the right dip is due to the absorption of the polymer. With this vertical antenna design, the dielectric gap can be made much smaller with an extremely small mode volume, making it a potential candidate for single ...


Modeling Elastic Instabilities In Nematic Elastomers, Badel L. Mbanga, Fangfu Ye, Jonathan Selinger, Robin Selinger Nov 2010

Modeling Elastic Instabilities In Nematic Elastomers, Badel L. Mbanga, Fangfu Ye, Jonathan Selinger, Robin Selinger

Chemical Physics Publications

Liquid crystal elastomers are cross-linked polymer networks covalently bonded with liquid crystal mesogens. In the nematic phase, due to strong coupling between mechanical strain and orientational order, these materials display strain-induced instabilities associated with formation and evolution of orientational domains. Using a three-dimensional finite element elastodynamics simulation, we investigate one such instability, the onset of stripe formation in a monodomain film stretched along an axis perpendicular to the nematic director. In our simulation, we observe the formation of striped domains with alternating director rotation. This model allows us to explore the fundamental physics governing dynamic mechanical response of nematic elastomers ...


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 ...


Second-Harmonic Generation In A Bent-Core Nematic Liquid Crystal, Seung Ho Hong, J. C. Williams, Robert J. Twieg, Antal Jakli, Jim T. Gleeson, Samuel N. Sprunt, Brett Ellman Oct 2010

Second-Harmonic Generation In A Bent-Core Nematic Liquid Crystal, Seung Ho Hong, J. C. Williams, Robert J. Twieg, Antal Jakli, Jim T. Gleeson, Samuel N. Sprunt, Brett Ellman

Chemical Physics Publications

Second-Second-harmonic generation (SHG) is studied in the magnetically aligned nematic phase of a bent-core liquid crystal (BCN) and compared to similar measurements made on a conventional rodlike (calamitic) nematic compound. The second-harmonic (SH) light detected from both materials is predominantly due to scattering and therefore incoherent. Results on the calamitic are consistent with a polarization induced by ordinary director fluctuations in the nematic phase. However, the SH scattering collected in the BCN exhibits a different temperature and angular dependence. We discuss how these differences could arise from the effects of short-range correlated, smectic-C-type molecular clusters, which have been detected in ...


The Ion Capturing Effect Of 5 Degrees Siox Alignment Films In Liquid Crystal Devices, Yi Huang, Philip J. Bos, Achintya Bhowmik Sep 2010

The Ion Capturing Effect Of 5 Degrees Siox Alignment Films In Liquid Crystal Devices, Yi Huang, Philip J. Bos, Achintya Bhowmik

Chemical Physics Publications

We show that SiOx, deposited at 5 degrees to the interior surface of a liquid crystal cell allows for a surprisingly substantial reduction in the ion concentration of liquid crystal devices. We have investigated this effect and found that this type of film, due to its surface morphology, captures ions from the liquid crystal material. Ion adsorption on 5 degrees SiOx film obeys the Langmuir isotherm. Experimental results shown allow estimation of the ion capturing capacity of these films to be more than an order of 10 000/mu m(2). These types of materials are useful for new types ...


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 ...


Raman Scattering Study Of Phase Biaxiality In A Thermotropic Bent-Core Nematic Liquid Crystal, Min Sang Park, Beom-Kin Yoon, Jung Ok Park, Veena Prasad, Satyendra Kumar, Mohan Srinivasarao Jul 2010

Raman Scattering Study Of Phase Biaxiality In A Thermotropic Bent-Core Nematic Liquid Crystal, Min Sang Park, Beom-Kin Yoon, Jung Ok Park, Veena Prasad, Satyendra Kumar, Mohan Srinivasarao

Physics Publications

Polarized Raman spectroscopy was used to investigate the development of orientational order and the degree of phase biaxiality in a bent-core mesogenic system. The values of the uniaxial order parameters ⟨P200⟩ and ⟨P400⟩, and biaxial order parameters ⟨P220⟩, ⟨P420⟩, and ⟨P440⟩, and their evolution with temperature were determined. The temperature dependence of almost all order parameters reveals a second order transition from the uniaxial to biaxial nematic phase with ⟨P220⟩ increasing to ∼0.22 before a first order transition to the smectic-C phase, upon cooling.


Surface Alignment And Anchoring Transitions In Nematic Lyotropic Chromonic Liquid Crystal, V. G. Nazarenko, O. P. Boiko, H. S. Park, O. M. Brodyn, M. M. Omelchenko, L. Tortora, Yuriy A. Nastishin, Oleg Lavrentovich Jun 2010

Surface Alignment And Anchoring Transitions In Nematic Lyotropic Chromonic Liquid Crystal, V. G. Nazarenko, O. P. Boiko, H. S. Park, O. M. Brodyn, M. M. Omelchenko, L. Tortora, Yuriy A. Nastishin, Oleg Lavrentovich

Chemical Physics Publications

The surface alignment of lyotropic chromonic liquid crystals can not only be planar (tangential) but also homeotropic, with self-assembled aggregates perpendicular to the substrate, as demonstrated by mapping optical retardation and by three-dimensional imaging of the director field. With time, the homeotropic nematic undergoes a transition into a tangential state. The anchoring transition is discontinuous and can be described by a double-well anchoring potential with two minima corresponding to tangential and homeotropic orientation.


Nematic Biaxiality In A Bent-Core Material, Hyungguen Yoon, Shin-Woong Kang, Ronald Y. Dong, Alberto Marini, Kattera A. Suresh, Mohan Srinivasarao, Satyendra Kumar May 2010

Nematic Biaxiality In A Bent-Core Material, Hyungguen Yoon, Shin-Woong Kang, Ronald Y. Dong, Alberto Marini, Kattera A. Suresh, Mohan Srinivasarao, Satyendra Kumar

Physics Publications

The results of a recent investigation of the nematic biaxiality in a bent-core mesogen (A131) are in apparent disagreement with earlier claims. Samples of mesogen A131 used in the two studies were investigated with polarized optical microscopy, conoscopy, carbon-13 NMR, and crossover frequency measurements. The results demonstrate that textural changes associated with the growth of biaxial nematic order appear at similar to 149 degrees C. The Maltese cross observed in the conoscopic figure gradually splits into two isogyres at lower temperatures indicating phase biaxiality. Presence of the uniaxial to biaxial nematic phase transition is further confirmed by temperature trends of ...


Dielectric Properties Of Mixtures Of A Bent-Core And A Calamitic Liquid Crystal, Peter Salamon, Nandor Éber, Agnes Buka, Jim T. Gleeson, Samuel N. Sprunt, Antal Jakli Mar 2010

Dielectric Properties Of Mixtures Of A Bent-Core And A Calamitic Liquid Crystal, Peter Salamon, Nandor Éber, Agnes Buka, Jim T. Gleeson, Samuel N. Sprunt, Antal Jakli

Chemical Physics Publications

Dielectric spectroscopy measurements have been performed on a bent-core nematic liquid crystal and on its binary mixtures with a calamitic nematic. We have detected more dispersions in the bent-core compound than in the calamitic one, including one at an unusually low frequency of a few kilohertz. The dispersions detected in the mixtures have been identified and the spectra have been split into contributions of the constituents. In order to connect the dielectric increment with the molecular dipole moment we have applied a sophisticated conformational calculation not performed before for a large, flexible mesogen molecule with numerous polar groups.


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 ...


Statistical Mechanics Of Splay Flexoelectricity In Nematic Liquid Crystals, Subas Dhakal, Jonathan Selinger Mar 2010

Statistical Mechanics Of Splay Flexoelectricity In Nematic Liquid Crystals, Subas Dhakal, Jonathan Selinger

Chemical Physics Publications

We develop a lattice model for the splay flexoelectric effect in nematic liquid crystals. In this model, each lattice site has a spin representing the local molecular orientation, and the interaction between neighboring spins represents pear-shaped molecules with shape polarity. We perform Monte Carlo simulations and mean-field calculations to find the behavior as a function of interaction parameters, temperature, and applied electric field. The resulting phase diagram has three phases: isotropic, nematic, and polar. In the nematic phase, there is a large splay flexoelectric effect, which diverges as the system approaches the transition to the polar phase. These results show ...


Giant Flexoelectricity In Bent-Core Nematic Liquid Crystal Elastomers, J. Harden, Martin Chambers, Rafael Verduzco, Paul Luchette, Jim T. Gleeson, Samuel N. Sprunt, Antal Jákli Mar 2010

Giant Flexoelectricity In Bent-Core Nematic Liquid Crystal Elastomers, J. Harden, Martin Chambers, Rafael Verduzco, Paul Luchette, Jim T. Gleeson, Samuel N. Sprunt, Antal Jákli

Chemical Physics Publications

Recently ferroelectric ceramic and bent-core nematic liquid crystals have demonstrated flexoelectricity (coupling between curvature strains to electric polarization) up to 10(4) times larger than the previous standards. This may allow for usable electromechanical devices. However, ceramics are too rigid to withstand large bending and bent-core nematic fluids must be physically supported-their technological applicability is still limited. In this paper, we show that novel side-chain bent-core nematic elastomers not only produce giant flexoelectricity but are also robust and flexible enough for microscale parasitic power generation. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3358391]


The Effect Of Siox Alignment Layer Thickness On The Switching Of Smc* Bistable Liquid Crystal Devices, Mitya Reznikov, Philip J. Bos, Michael J. O'Callaghan Jan 2010

The Effect Of Siox Alignment Layer Thickness On The Switching Of Smc* Bistable Liquid Crystal Devices, Mitya Reznikov, Philip J. Bos, Michael J. O'Callaghan

Chemical Physics Publications

SiOx alignment layers have been shown to allow defect-free SmC* devices with near optimum bistable orientation of the director. In this paper we investigate the effect of the thickness of this type of alignment layer on the required amplitude of an applied voltage pulse to cause bistable switching. The results of an experimental investigation and simple model are presented. We find that for thicker layers, the amplitude is controlled by the voltage drop across the alignment layers and by the effect of polar interactions between the liquid crystal (LC) and the alignment layers. For thin alignment layers the amplitude is ...