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Articles 1 - 11 of 11

Full-Text Articles in Physics

Electrically Reconfigurable Optical Metamaterial Based On Colloidal Dispersion Of Metal Nanorods In Dielectric Fluid, Andrii B. Golovin, Oleg Lavrentovich Dec 2009

Electrically Reconfigurable Optical Metamaterial Based On Colloidal Dispersion Of Metal Nanorods In Dielectric Fluid, Andrii B. Golovin, Oleg Lavrentovich

Chemical Physics Publications

Optical metamaterials capture the imagination with breathtaking promises of nanoscale resolution in imaging and invisibility cloaking. We demonstrate an approach to construct a metamaterial in which metallic nanorods, of dimension much smaller than the wavelength of light, are suspended in a fluid and placed in a nonuniform electric field. The field controls the spatial distribution and orientation of nanorods because of the dielectrophoretic effect. The field-controlled placement of nanorods causes optical effects such as varying refractive index, optical anisotropy (birefringence), and reduced visibility of an object enclosed by the metamaterial.


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 ...


Optical Waveguiding In Bent-Core Liquid-Crystal Filaments, Jake Fontana, C. Bailey, Wolfgang Weissflog, I. Janossy, Antal Jakli Sep 2009

Optical Waveguiding In Bent-Core Liquid-Crystal Filaments, Jake Fontana, C. Bailey, Wolfgang Weissflog, I. Janossy, Antal Jakli

Chemical Physics Publications

We demonstrate optical waveguiding in recently discovered free-standing bent-core liquid-crystal filaments. The bent-core liquid-crystal molecules in air self-assemble into a cylindrical geometry that is "solidlike" along the radial direction of the filament and liquid in the axial direction of the filament. These filaments are unique not only because they are fluids, but also because they are anisotropic. For this reason, their waveguiding properties not predictable need to be characterized. The light power transmitted through the filament was found to be independent of temperature from 180 degrees C to near room temperature. Initial defects of newly pulled filaments were found to ...


Flexoelectricity Of A Calamitic Liquid Crystal Elastomer Swollen With A Bent-Core Liquid Crystal, Martin Chambers, Rafael Verduzco, Jim T. Gleeson, Samuel N. Sprunt, Antal Jakli Sep 2009

Flexoelectricity Of A Calamitic Liquid Crystal Elastomer Swollen With A Bent-Core Liquid Crystal, Martin Chambers, Rafael Verduzco, Jim T. Gleeson, Samuel N. Sprunt, Antal Jakli

Chemical Physics Publications

We have measured the electric current induced by mechanical distortion of a calamitic liquid crystal elastomer (LCE) swollen with a low molecular weight bent-core nematic (BCN) liquid crystal, and have determined, for the first time, the bend flexoelectric coefficient e(3) of such a BCN-LCE composite. In one method, we utilise air-pressure to induce a mechanical bend deformation and flexoelectric polarization in a BCN-LCE film, and then measure the polarization current as a function of time. An alternative technique uses a rotary-motor driven scotch yoke to periodically flex the BCN-LCE; in this case, the magnitude and phase of the induced ...


Cholesteric Liquid-Crystal Displays Illuminated By Diffuse And Partially Diffuse Light, W. D. St. John, Z. J. Lu, J. William Doane, Bahman Taheri Jul 2009

Cholesteric Liquid-Crystal Displays Illuminated By Diffuse And Partially Diffuse Light, W. D. St. John, Z. J. Lu, J. William Doane, Bahman Taheri

Chemical Physics Publications

We report on the photometric and colorimetric properties of surface and polymer network stabilized reflective cholesteric displays. Both diffuse and partially diffuse illumination are used, the latter being an experimental approach to emulating typical room light conditions. It is shown that addition of polymer increases the field of view while decreasing angular dependence of the color quantities: hue, chroma, and lightness. Total luminance and contrast ratio, however, are also decreased. Therefore, it is concluded that optimum polymer concentration is dependent on the viewing geometry. Luminance and contrast ratio of the surface stabilized cells exceeded that of polymer stabilized cell when ...


Design Of A Wide Bandwidth Switchable Mirror Based On A Liquid Crystal Etalon, Enkh-Amgalan Dorjgotov, Philip J. Bos, Achintya Bhowmik May 2009

Design Of A Wide Bandwidth Switchable Mirror Based On A Liquid Crystal Etalon, Enkh-Amgalan Dorjgotov, Philip J. Bos, Achintya Bhowmik

Chemical Physics Publications

We propose the design for a switchable mirror with high efficiency and a 30 nm bandwidth. The device is based on a liquid crystal filled etalon. Broad bandwidth is achieved through the use of integrated half-wave layers into the dielectric stack design, while high efficiency is achieved using a polarization independent liquid crystal effect. Potential applications in the area of displays are also presented.


Theory Of Ferroelectric Nanoparticles In Nematic Liquid Crystals, Lena M. Lopatina, Jonathan Selinger May 2009

Theory Of Ferroelectric Nanoparticles In Nematic Liquid Crystals, Lena M. Lopatina, Jonathan Selinger

Chemical Physics Publications

Recent experiments have reported that ferroelectric nanoparticles have drastic effects on nematic liquid crystals-increasing the isotropic-nematic transition temperature by about 5 K, and greatly increasing the sensitivity to applied electric fields. To understand these effects, we develop a theory for the statistical mechanics of ferroelectric nanoparticles in liquid crystals. This theory predicts the enhancements of liquid-crystal properties, in good agreement with experiments. These predictions apply even when electrostatic interactions are partially screened by moderate concentrations of ions.


Electro-Optic Technique To Study Biaxiality Of Liquid Crystals With Positive Dielectric Anisotropy: The Case Of A Bent-Core Material, Khoa Van Le, Manoj Mathews, Martin Chambers, John Harden, Quan Li, Hideo Takezoe, Antal Jákli Mar 2009

Electro-Optic Technique To Study Biaxiality Of Liquid Crystals With Positive Dielectric Anisotropy: The Case Of A Bent-Core Material, Khoa Van Le, Manoj Mathews, Martin Chambers, John Harden, Quan Li, Hideo Takezoe, Antal Jákli

Chemical Physics Publications

We propose that, for materials having positive dielectric anisotropy, the biaxiality can be clearly verified or excluded by measuring the transmitted light intensity as a function of electric field. If the material is biaxial and is observed in homeotropically aligned cells, the schlieren texture should not disappear (transmitted intensity is not zero) even at very high fields, since the field does not affect the distribution of the second director normal to the main director. On the other hand, if the material is uniaxial the transmitted intensity should decrease with increasing field and a perfect homeotropic texture can be achieved at ...


Nonphotochemical Laser-Induced Nucleation Of Nematic Phase And Alignment Of Nematic Director From A Supercooled Thermotropic Liquid Crystal, Xiaoying Sun, Bruce A. Garetz, Michele F. Moreira, Peter Palffy-Muhoray Feb 2009

Nonphotochemical Laser-Induced Nucleation Of Nematic Phase And Alignment Of Nematic Director From A Supercooled Thermotropic Liquid Crystal, Xiaoying Sun, Bruce A. Garetz, Michele F. Moreira, Peter Palffy-Muhoray

Chemical Physics Publications

A nonphotochemical laser-induced phase transition was studied in a supercooled 4′‐n-pentyl-4-cyanobiphenyl (5CB, also referred to as PCB and K15) liquid crystal, using linearly polarized 45 ps light pulses at a wavelength of 532 nm. The laser induced nucleation from the metastable supercooled isotropic phase to the nematic phase during slow cooling (0.001 °C∕min) and high light intensity (3.9 MW∕cm2). The resulting nematic director tended to be aligned along the direction of the plane of polarization of the light. At the intensities used, there is no observable laser-induced realignment of the director once the sample ...


Chirality Of Lipids Makes Fluid Lamellar Phases Piezoelectric, John Harden, Nicholas Diorio, Alexander G. Petrov, Antal Jakli Jan 2009

Chirality Of Lipids Makes Fluid Lamellar Phases Piezoelectric, John Harden, Nicholas Diorio, Alexander G. Petrov, Antal Jakli

Chemical Physics Publications

The role of chirality in membrane-forming lipids is not well appreciated at present. Here we demonstrate that the chirality of phospholipids makes fluid lipid bilayers piezoelectric. Thus, chiral lipids would play a central role in the functioning of cell membranes as active mechanotransducers. By periodically shearing and compressing nonaqueous lamellar phases of left (L-alpha-phosphatidylcholine), right (D-alpha-phosphatidylcholine), and racemic (DL-alpha-phosphatidylcholine) lipids, we induced a tilt of the molecules with respect to the bilayer's normal and produced electric current perpendicular to the tilt plane, with the chiral lipids only. This effect is due to the Sm-A(*) phase liquid crystal structure of ...


Control Of Viscous Fingering Patterns In A Radial Hele-Shaw Cell, Shuwang Li, John S. Lowengrub, Jake Fontana, Peter Palffy-Muhoray Jan 2009

Control Of Viscous Fingering Patterns In A Radial Hele-Shaw Cell, Shuwang Li, John S. Lowengrub, Jake Fontana, Peter Palffy-Muhoray

Chemical Physics Publications

We study numerically and experimentally the dynamics and control of viscous fingering patterns in a circular Hele-Shaw cell. The nonlocality and nonlinearity of the system, especially interactions among developing fingers, make the emergent pattern difficult to predict and control. By controlling the injection rate of the less viscous fluid, we can precisely suppress the evolving interfacial instabilities. There exist denumerable attractive, self-similarly evolving symmetric, universal shapes. Experiments confirm the feasibility of the control strategy, which is summarized in a morphology diagram.