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Articles 1 - 19 of 19

Full-Text Articles in Physics

Spatial And Orientational Control Of Liquid Crystal Alignment Using A Surface Localized Polymer Layer, Lu Lu, Tatiana Sergan, Vassili Sergan, Philip J. Bos Dec 2012

Spatial And Orientational Control Of Liquid Crystal Alignment Using A Surface Localized Polymer Layer, Lu Lu, Tatiana Sergan, Vassili Sergan, Philip J. Bos

Chemical Physics Publications

We present an alignment method for the surface contacting liquid crystal (LC) director. This method allows complete control of the polar pretilt angle as a function of position in a liquid crystal device, and has the potential of controlling the azimuthal orientation of LC. Important considerations of this method are to form a thin layer of reactive monomers at the LC cell interior surface, and to control the deleterious effects of flow due to polymerization induced concentration gradients. To achieve these, the voltage and frequency of the applied electric field and the UV intensity during the polymerization process are significant.


Mechanism Of Electric-Field-Induced Segregation Of Additives In A Liquid-Crystal Host, Lu Lu, Vassili Sergan, Philip J. Bos Nov 2012

Mechanism Of Electric-Field-Induced Segregation Of Additives In A Liquid-Crystal Host, Lu Lu, Vassili Sergan, Philip J. Bos

Chemical Physics Publications

The mechanism for electric-field-induced segregation of additives, containing a polar group, in a host liquid crystal is proposed. It is shown that the polarity of an applied dc electric field, or the frequency of an ac electric field, strongly influences the segregation of reactive monomers containing an ester group. An explanation of this result is offered based on the association of dissolved ions with polar groups of the reactive monomers. This association is considered to cause these types of additives to drift to the cell surface in the presence of an external electric field. The described mechanism can be applied ...


Doping The Nematic Liquid Crystal 5cb With Milled Batio3 Nanoparticles, Alexander Lorenz, Natalie Zimmerman, Satyendra Kumar, Dean R. Evans, Gary Cook, Hienz-S. Kitzerow Nov 2012

Doping The Nematic Liquid Crystal 5cb With Milled Batio3 Nanoparticles, Alexander Lorenz, Natalie Zimmerman, Satyendra Kumar, Dean R. Evans, Gary Cook, Hienz-S. Kitzerow

Physics Publications

The simple nematic mesogen 5CB was doped with milled BaTiO3 nanoparticles and was investigated with x-ray scattering. Doping with BaTiO3 nanoparticles of 9 nm in diameter led to the formation of crystallites. These crystallites precipitated and formed a waxlike nanodispersion of 5CB and nanoparticles, which led to intense x-ray scattering signals characteristic of a multilayer structure. Surprisingly, the multilayers possess unusual interlayer spacing, which cannot be explained by simple smectic order of the calamitic molecules.


Multichannel Parametrization Of Pi N Scattering Amplitudes And Extraction Of Resonance Parameters, Manoj Shrestha, D. Mark Manley Nov 2012

Multichannel Parametrization Of Pi N Scattering Amplitudes And Extraction Of Resonance Parameters, Manoj Shrestha, D. Mark Manley

Physics Publications

We present results of a new multichannel partial-wave analysis for πN scattering in the c.m. energy range 1080 to 2100 MeV. This work explicitly includes ηN and KΛ channels and the single pion photoproduction channel. Resonance parameters were extracted by fitting partial-wave amplitudes from all considered channels using a multichannel parametrization that is consistent with S-matrix unitarity. The resonance parameters so obtained are compared to predictions of quark models.


Partial-Wave Analysis Of The Pi- + Proton Goes To Eta Meson + Neutron And Pi- + Proton Goes To Neutral Kaon + Lambda Reactions, Manoj Shrestha, D. Mark Manley Oct 2012

Partial-Wave Analysis Of The Pi- + Proton Goes To Eta Meson + Neutron And Pi- + Proton Goes To Neutral Kaon + Lambda Reactions, Manoj Shrestha, D. Mark Manley

Physics Publications

We investigate the hadronic reactions πN→ηN and πN→KΛ via single-energy partial-wave analyses in the c.m. energy range 1080 to 2100 MeV. Our results for the KΛ channel are consistent with prior works; however, for the ηNchannel our results differ significantly from previous energy-dependent partial-wave analyses that violate the S-matrix unitarity. We present results of ηN and KΛ partial-wave amplitudes constrained by a unitary energy-dependent model. We obtain excellent predictions of integrated cross sections for the two reactions from a global energy-dependent solution. Our results imply that the region just above S11(1535) has a major contribution from ...


Deformation Of An Asymmetric Thin Film, Jun Geng, Jonathan V. Selinger Sep 2012

Deformation Of An Asymmetric Thin Film, Jun Geng, Jonathan V. Selinger

Chemical Physics Publications

Experiments have investigated shape changes of polymer films induced by asymmetric swelling by a chemical vapor. Inspired by recent work on the shaping of elastic sheets by non-Euclidean metrics [ Y. Klein, E. Efrati and E. Sharon Science 315 1116 (2007)], we represent the effect of chemical vapors by a change in the target metric tensor. In this problem, unlike that earlier work, the target metric is asymmetric between the two sides of the film. Changing this metric induces a curvature of the film, which may curve into a partial cylinder or a partial sphere. We calculate the elastic energy for ...


Direct Observation Of Smectic Layers In Thermotropic Liquid Crystals, C. Zhang, M. Gao, Wolfgang Weissflog, Ute Baumeister, Samuel N. Sprunt, Jim T. Gleeson, Antal Jákli Sep 2012

Direct Observation Of Smectic Layers In Thermotropic Liquid Crystals, C. Zhang, M. Gao, Wolfgang Weissflog, Ute Baumeister, Samuel N. Sprunt, Jim T. Gleeson, Antal Jákli

Chemical Physics Publications

We demonstrate subnanometer resolution cryo-TEM imaging of smectic layers in the smectic and nematic phases of two bent-core liquid crystals. Our results show perfect periodicity over several hundred layers in the smectic phase and also provide the first direct evidence of smectic clusters on length scales of 30-50 nm in a nematic liquid crystal. The results are corroborated with small angle x-ray scattering measurements. The observation of smectic clusters in the nematic phase is of special interest in bent-core liquid crystals, where the smectic clusters are stable over wide temperature ranges, in contrast to the well-known pretransitional "cybotactic" clusters that ...


Biaxial Nematic Order Induced By Smectic Fluctuations, C. Zhang, S. Chakraborty, T. Ostapenko, Samuel N. Sprunt, Antal Jakli, Jim T. Gleeson Aug 2012

Biaxial Nematic Order Induced By Smectic Fluctuations, C. Zhang, S. Chakraborty, T. Ostapenko, Samuel N. Sprunt, Antal Jakli, Jim T. Gleeson

Chemical Physics Publications

We report on a series of measurements on the microscopic structure and the magneto-optical properties of a calamitic liquid crystalline compound in its nematic phase. Structural studies show the existence of short-range, tilted smectic order consistent with pretransitional effects above an underlying smectic phase. Concomitantly, magneto-optical results exhibit the existence of an optic axis not collinear with the uniaxial director. This apparent biaxial nature is discussed within the context of coupling between the tensor nematic and the smectic order parameters.


Light Scattering From Liquid Crystal Director Fluctuations In Steady Magnetic Fields Up To 25 Tesla, Pavan K. Challa, O. Curtiss, J. C. Williams, Robert J. Twieg, J. Toth, S. Mcgill, Jim T. Gleeson, Antal Jakli, Samuel N. Sprunt Jul 2012

Light Scattering From Liquid Crystal Director Fluctuations In Steady Magnetic Fields Up To 25 Tesla, Pavan K. Challa, O. Curtiss, J. C. Williams, Robert J. Twieg, J. Toth, S. Mcgill, Jim T. Gleeson, Antal Jakli, Samuel N. Sprunt

Chemical Physics Publications

We report on homodyne dynamic light scattering measurements of orientational fluctuation modes in both calamitic and bent-core nematic liquid crystals, carried out in the new split-helix resistive magnet at the National High Magnetic Field Laboratory. The relaxation rate and inverse scattered intensity of director fluctuations exhibit a linear dependence on field-squared up to 25 tesla, which is consistent with strictly lowest order coupling of the tensor order parameter Q to field (Q(alpha beta)B(alpha)B(beta)) in the nematic free energy. However, we also observe evidence of field dependence of certain nematic material parameters, an effect which may ...


Elasticity Of Lyotropic Chromonic Liquid Crystals Probed By Director Reorientation In A Magnetic Field, Shuang Zhou, Yuriy A. Nastishin, M. M. Omelchenko, L. Tortora, V. G. Nazarenko, O. P. Boiko, T. Ostapenko, T. Hu, C. C. Almasan, Jim T. Gleeson, Oleg Lavrentovich Jul 2012

Elasticity Of Lyotropic Chromonic Liquid Crystals Probed By Director Reorientation In A Magnetic Field, Shuang Zhou, Yuriy A. Nastishin, M. M. Omelchenko, L. Tortora, V. G. Nazarenko, O. P. Boiko, T. Ostapenko, T. Hu, C. C. Almasan, Jim T. Gleeson, Oleg Lavrentovich

Chemical Physics Publications

Using a magnetic Frederiks transition technique, we measure the temperature and concentration dependences of splay K1, twistK2, and bend K3 elastic constants for the lyotropic chromonic liquid crystal sunset yellow formed through noncovalent reversible aggregation of organic molecules in water. K1 and K3 are comparable to each other and are an order of magnitude higher thanK2. At higher concentrations and lower temperatures, K1 and the ratios K1/K3 and K1/K2 increase, which is attributed to elongation of self-assembled lyotropic chromonic liquid crystal aggregates, a feature not ...


Polarization Conversion With Elliptical Patch Nanoantennas, Feng Wang, Ayan Chakrabarty, Fred Minkowski, Kai Sun, Qi-Huo Wei Jul 2012

Polarization Conversion With Elliptical Patch Nanoantennas, Feng Wang, Ayan Chakrabarty, Fred Minkowski, Kai Sun, Qi-Huo Wei

Chemical Physics Publications

In this paper, we demonstrate arrays of optical patch nanoantennas can convert light polarization through reflection. By breaking the azimuthal symmetry, elliptical plasmonic patch nanoantennas exhibit both even and odd cavity modes, which can be expressed by Mathieu functions. It is shown that by properly orienting the incident polarization, a linearly polarized light in resonance with one cavity mode can be converted into an elliptical or circular polarization after reflection. Since the major cavity modes can be excited at all incident angles, the polarization conversion by these elliptical patch nanoantennas can be realized with wide range of incident angles.


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 ...


Photoisomerization-Controlled Phase Segregation In A Submicron Confined Azonematic Liquid Crystal, B. Zupančič, S. Diez-Berart, D. Finotello, Oleg Lavrentovich, V. Zalar Jun 2012

Photoisomerization-Controlled Phase Segregation In A Submicron Confined Azonematic Liquid Crystal, B. Zupančič, S. Diez-Berart, D. Finotello, Oleg Lavrentovich, V. Zalar

Chemical Physics Publications

Deuteron nuclear magnetic resonance is used to study the phase segregation behavior of photoisomerizable liquid crystal diheptylazobenzene (7AB) confined into cylindrical pores of Anopore membranes. It is demonstrated that the concentration of both components in a binary trans-7AB and cis-7AB mixture can be controlled dynamically using UV-illumination stimulated trans-to-cisphotoisomerization and thermally induced cis-to-trans backisomerization. The so far elusive temperature-concentration phase diagram of such system is determined by comparative analysis of the behavior in bulk, thin-planar, and Anopore-confining geometry.


The Effect Of Salt On Ion Adsorption On A Siox Alignment Film And Reduced Conductivity Of A Liquid Crystal Host, Yi Huang, Achintya Bhowmik, Philip J. Bos Jun 2012

The Effect Of Salt On Ion Adsorption On A Siox Alignment Film And Reduced Conductivity Of A Liquid Crystal Host, Yi Huang, Achintya Bhowmik, Philip J. Bos

Chemical Physics Publications

It is shown that the addition of salt to liquid crystal cells, using a SiOx alignment layer, can actually reduce the ion concentration. This seeming contradiction may be explained by the ability of salt to complex with water and to aid the drying of the liquid crystal material. The results show a pathway to purifying liquid crystal devices to the extent needed for low-power low-refresh rate displays for e-book applications.


Dielectric Technique To Measure The Twist Elastic Constant Of Liquid Crystals: The Case Of A Bent-Core Material, Peter Salamon, Nandor Éber, J. Seltmann, M. Lehmann, Jim T. Gleeson, Samuel N. Sprunt, Antal Jákli Jun 2012

Dielectric Technique To Measure The Twist Elastic Constant Of Liquid Crystals: The Case Of A Bent-Core Material, Peter Salamon, Nandor Éber, J. Seltmann, M. Lehmann, Jim T. Gleeson, Samuel N. Sprunt, Antal Jákli

Chemical Physics Publications

The effect of director pretilt on the twist magnetic Freedericksz transition of nematics was investigated in a planar cell. The director configuration was calculated as a function of magnetic inductance. The dielectric and optical response of the nematic liquid crystal was numerically modeled. A dielectric measurement method for determining the elastic constant K-22 is presented. The influence of the conditions for the Mauguin effect is discussed. The theoretical predictions were confirmed by our experiments. Experimental data for all elastic constants of a bent-core nematic material are presented and discussed.


Azimuthal Dependence Of Switching Field Strength For Nematic Liquid Crystal Bistability On Patterned Alignment Layers, Jun-Ichi Niitsuma, Makoto Yoneya, Hiroshi Yokoyama May 2012

Azimuthal Dependence Of Switching Field Strength For Nematic Liquid Crystal Bistability On Patterned Alignment Layers, Jun-Ichi Niitsuma, Makoto Yoneya, Hiroshi Yokoyama

Chemical Physics Publications

We investigate the azimuthal dependence of the switching field strength for nematic liquid crystal bistability on patterned alignment layers to determine the validity of a switching theory proposed by Kim et al. [Appl. Phys. Lett. 78, 3055 (2001)] and to evaluate higher-order azimuthal anchoring coefficients. Director behavior during switching is described in detail for general azimuthal directions of an applied electric field and the experimental results are explained on the basis of the theory. We obtain azimuthal anchoring coefficients up to the second higher-order term in an expansion of the anchoring energy function. Detailed analysis of the director behavior reveals ...


Highly Piezoelectric Biocompatible And Soft Composite Fibers, J. Morvan, E. Buyuktanir, John L. West, Antal Jakli Feb 2012

Highly Piezoelectric Biocompatible And Soft Composite Fibers, J. Morvan, E. Buyuktanir, John L. West, Antal Jakli

Chemical Physics Publications

We report the fabrication of highly piezoelectric biocompatible soft fibers containing barium titanate ferroelectric ceramic particles dispersed in electrospun poly lactic acid (PLA). These fibers form mats that have two orders of magnitude larger piezoelectric constant per weight than single crystal barium titanate films. We propose that the observed apparent piezoelectricity results from the electrospinning induced polar alignment of the ferroelectric particles that pole the fibers similar to ferroelectret polymer foams that are poled by corona discharge. Due to the biocompatibility of PLA that encases the ferroelectric particles, these mats can be used in biological applications such as bio-sensors, artificial ...


Surface Wrinkling In Liquid Crystal Elastomers, Aditya Agrawal, Paul Luchette, Peter Palffy-Muhoray, Sibani Lisa Biswal, Walter G. Chapman, Rafael Verduzco Jan 2012

Surface Wrinkling In Liquid Crystal Elastomers, Aditya Agrawal, Paul Luchette, Peter Palffy-Muhoray, Sibani Lisa Biswal, Walter G. Chapman, Rafael Verduzco

Chemical Physics Publications

Structured surfaces give rise to novel and potentially useful properties such as controllable wettability and structural colour. Here, we demonstrate structured surfaces via reversible surface wrinkling in liquid crystal elastomers (LCEs). A thin polymer film deposited on top of a shape-responsive LCE exhibits a reversible, periodic surface wrinkling pattern in response to temperature changes. The orientation of the wrinkles depends on the orientation of the nematic director and the temperature at which the bilayer is prepared, and the wrinkles can be re-oriented in a single sample by heating or cooling the sample above or below the preparation temperature. We show ...


Alignment Layers With Variable Anchoring Strengths From Polyvinyl Alcohol, Yue Cui, Rafael S. Zola, Young-Cheol Yang, Deng-Ke Yang Jan 2012

Alignment Layers With Variable Anchoring Strengths From Polyvinyl Alcohol, Yue Cui, Rafael S. Zola, Young-Cheol Yang, Deng-Ke Yang

Chemical Physics Publications

In the study of polyvinyl alcohol (PVA) alignment layers for liquid crystal devices, we found that the anchoring strength can be greatly varied by changing the alignment film thickness. Both the polar and azimuthal anchoring strengths increased with increasing film thickness; however, they had different film thickness dependences. It was also noticed that the quartic term in the expansion of the Rapini-Papoular anchoring energy was important for describing the polar anchoring. In the experiment, solid PVA was dissolved in a thinner and spin-coated on glass substrates to create alignment layers. The substrates were assembled to make electrically-controlled birefringence liquid crystal ...