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Full-Text Articles in Physics

Note: Automated Maskless Micro-Multidomain Photoalignment, Christopher Culbreath, Nikolaus Glazar, Hiroshi Yokoyama Dec 2011

Note: Automated Maskless Micro-Multidomain Photoalignment, Christopher Culbreath, Nikolaus Glazar, Hiroshi Yokoyama

Chemical Physics Publications

We present a fully automated maskless exposure system for the fabrication of microscopic orientational surface alignment patterns. The maskless system allows us to fabricate arbitrary surface patterns over a 2 mm × 2 mm area with a resolution of 2.2 μm. A confocal autofocus system insures accurate and repeatable focus. Microscopic orientational surface patterns have been demonstrated to exhibit a variety of novel functionalities, such as surface alignment multi-stability.


Maier-Saupe-Type Theory Of Ferroelectric Nanoparticles In Nematic Liquid Crystals, Lena M. Lopatina, Jonathan V. Selinger Oct 2011

Maier-Saupe-Type Theory Of Ferroelectric Nanoparticles In Nematic Liquid Crystals, Lena M. Lopatina, Jonathan V. Selinger

Chemical Physics Publications

Several 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. In a recent paper [Lopatina and Selinger, Phys. Rev. Lett. 102, 197802 (2009)], we modeled these effects through a Landau theory, based on coupled orientational order parameters for the liquid crystal and the nanoparticles. This model has one important limitation: Like all Landau theories, it involves an expansion of the free energy in powers of the order parameters, and hence it overestimates the order parameters that occur in the ...


Magneto-Optical Technique For Detecting The Biaxial Nematic Phase, T. Ostapenko, C. Zhang, Samuel N. Sprunt, Antal Jákli, Jim T. Gleeson Aug 2011

Magneto-Optical Technique For Detecting The Biaxial Nematic Phase, T. Ostapenko, C. Zhang, Samuel N. Sprunt, Antal Jákli, Jim T. Gleeson

Chemical Physics Publications

The existence of the elusive biaxial phase has been the subject of much discussion since it was predicted by Freiser in 1970. More recently, there have been numerous attempts to find a thermotropic liquid crystal that exhibits a biaxial phase and with this, conflicting reports about whether such a phase has been positively identified in bent-core liquid crystals. One reason for the discrepancy is that there is currently no way to rule out surface effects or anchoring transitions, both of which may give a false positive identification of a uniaxial-biaxial nematic transition. We have developed a technique that uses a ...


Solar To Electrical Conversion Via Liquid Crystal Elastomers, T. Hiscock, M. Warner, Peter Palffy-Muhoray Jun 2011

Solar To Electrical Conversion Via Liquid Crystal Elastomers, T. Hiscock, M. Warner, Peter Palffy-Muhoray

Chemical Physics Publications

We have constructed a hypothetical charge pump which converts solar energy into DC electricity. The output is generated by cyclic changes in the capacitance of a circuit, which transfers charge from a low to a high voltage. The electric field across the capacitor must be of the order of 10(8)Vm(-1) to compete with efficiencies of photovoltaics. We have modeled the output using a liquid crystal elastomer as the working substance. Efficiencies of 1 - 4% are obtained, and are enhanced by careful choices in the capacitor geometries and the operating voltages of the charge pump. (C) 2011 American ...


Nanostructures Of Liquid Crystal Phases In Mixtures Of Bent-Core And Rod-Shaped Molecules, Seung Ho Hong, Rafael Verduzco, Jim T. Gleeson, Samuel N. Sprunt, Antal Jakli Jun 2011

Nanostructures Of Liquid Crystal Phases In Mixtures Of Bent-Core And Rod-Shaped Molecules, Seung Ho Hong, Rafael Verduzco, Jim T. Gleeson, Samuel N. Sprunt, Antal Jakli

Chemical Physics Publications

We report small angle x-ray scattering (SAXS) studies of isotropic, nematic, and smectic mesophases formed by binary mixtures of bent-core (BC) and rod-shaped (RS) molecules. While optical studies indicate that the components are fully miscible, SAXS reveals fascinating structures that are consistent with segregation on a nanoscopic scale. We find that tilted smectic clusters, which have been previously reported in both the nematic and isotropic states of the pure BC materials, are also present in mixtures with up to 50 wt% of the RS compound; this is consistent with previous dielectric and flexoelectric studies on such mixtures. Unexpectedly in this ...


One Order Parameter Tensor Mean Field Theory For Biaxial Liquid Crystals, Xiaoyu Zheng, Peter Palffy-Muhoray Mar 2011

One Order Parameter Tensor Mean Field Theory For Biaxial Liquid Crystals, Xiaoyu Zheng, Peter Palffy-Muhoray

Chemical Physics Publications

In this paper, we present a simple one tensor mean field model of biaxial nematic liquid crystals. The salient feature of our approach is that material parameters appear explicitly in the order parameter tensor. We construct the free energy from a mean field potential based on anisotropic dispersion interactions, identify the order parameter tensor and its elements, and obtain self-consistent equations, which are then solved numerically. The results are illustrated in a 3D ternary phase diagram. The phase behavior can be simply related to molecular parameters. The results may be useful for designing molecules that show a thermotropic biaxial phase.


Effect Of Trans-Cis Photoisomerization On Phase Equilibria And Phase Transition Of Liquid-Crystalline Azobenzene Chromophore And Its Blends With Reactive Mesogenic Diacrylate, Namil Kim, Quan Li, Thein Kyu Mar 2011

Effect Of Trans-Cis Photoisomerization On Phase Equilibria And Phase Transition Of Liquid-Crystalline Azobenzene Chromophore And Its Blends With Reactive Mesogenic Diacrylate, Namil Kim, Quan Li, Thein Kyu

Chemical Physics Publications

Photoisomerization-induced phase transition of neat liquid-crystalline azobenzene chromophore (LCAC) and its effect on phase diagrams of its mixtures with reactive mesogenic diacrylate monomer (RM257) have been investigated experimentally and theoretically. Upon irradiation with ultraviolet light, the nematic phase of LCAC transformed to isotropic, while the crystal phase showed corrugated textures on the surface (i.e., ripples). The phase-transition temperatures and corresponding morphologies of the blends have been investigated by means of differential scanning calorimetry and optical microscopy. A theoretical phase diagram of a binary nematic and crystalline system was constructed by self-consistently solving the combined free energies of Flory-Huggins, Maier-Saupe ...


Elastic Constants And Orientational Viscosities Of A Bent-Core Nematic Liquid Crystal, Madhabi Majumdar, Peter Salamon, Antal Jákli, Jim T. Gleeson, Samuel N. Sprunt Mar 2011

Elastic Constants And Orientational Viscosities Of A Bent-Core Nematic Liquid Crystal, Madhabi Majumdar, Peter Salamon, Antal Jákli, Jim T. Gleeson, Samuel N. Sprunt

Chemical Physics Publications

Using a combination of dynamic light scattering and Freedericksz transitions induced in applied magnetic and electric fields, we have determined the absolute magnitudes of the Frank elastic constants and effective orientational viscosities of the bent-core nematic liquid crystal, 4-chloro-1,3-phenylene bis 4-[4'-(9-decenyloxy)benzoyloxy] benzoate. At a fixed temperature 2 degrees C below the isotropic-nematic transition, we find K(11) = 3.1 x 10(-12) N, K(22) = 0.31 x 10(-12) N, K(33) = 0.88 x 10(-12) N, eta(splay) = 1.1 Pa s, eta(twist) = 0.37 Pa s, and eta(bend) = 1.2 ...


Chirality And Biaxiality In Cholesteric Liquid Crystals, Subas Dhakal, Jonathan Selinger Feb 2011

Chirality And Biaxiality In Cholesteric Liquid Crystals, Subas Dhakal, Jonathan Selinger

Chemical Physics Publications

We investigate the statistical mechanics of chirality and biaxiality in liquid crystals through a variety of theoretical approaches, including Monte Carlo simulations, lattice mean-field theory, and Landau theory. All of these calculations show that there is an important interaction between cholesteric twist and biaxial order: The twist acts as a field on the biaxial order, and conversely, the biaxial order increases the twist, that is, reduces the pitch. We model the behavior of chiral biaxial liquid crystals as a function of temperature and discuss how the predictions can be tested in experiments.


Electro-Optic Effects In Colloidal Dispersion Of Metal Nano-Rods In Dielectric Fluid, Andrii B. Golovin, Jie Xiang, Heung-Shik Park, Luana Tortora, Yuriy A. Nastishin, Sergij V. Shyiyanovskii, Oleg Lavrentovich Feb 2011

Electro-Optic Effects In Colloidal Dispersion Of Metal Nano-Rods In Dielectric Fluid, Andrii B. Golovin, Jie Xiang, Heung-Shik Park, Luana Tortora, Yuriy A. Nastishin, Sergij V. Shyiyanovskii, Oleg Lavrentovich

Chemical Physics Publications

In modern transformation optics, one explores metamaterials with properties that vary from point to point in space and time, suitable for application in devices such as an "optical invisibility cloak" and an "optical black hole". We propose an approach to construct spatially varying and switchable metamaterials that are based on colloidal dispersions of metal nano-rods (NRs) in dielectric fluids, in which dielectrophoretic forces, originating in the electric field gradients, create spatially varying configurations of aligned NRs. The electric field controls orientation and concentration of NRs and thus modulates the optical properties of the medium. Using gold (Au) NRs dispersed in ...


Inelastic Collisions And Anisotropic Aggregation Of Particles In A Nematic Collider Driven By Backflow, Oleg P. Pishnyak, Sergij V. Shiyanovskii, Oleg Lavrentovich Jan 2011

Inelastic Collisions And Anisotropic Aggregation Of Particles In A Nematic Collider Driven By Backflow, Oleg P. Pishnyak, Sergij V. Shiyanovskii, Oleg Lavrentovich

Chemical Physics Publications

We design a nematic collider for controlled out-of-equilibrium anisotropic aggregation of spherical colloidal particles. The nematic surrounding imparts dipolar interactions among the spheres. A bidirectional backflow of the nematic liquid crystal in a periodic electric field forces the spheres to collide with each other. The inelastic collisions are of two types, head to tail and head to head. Head-to-tail collisions of dipoles result in longitudinal aggregation while head-to-head collisions promote aggregation in the transversal direction. The frequency of head-to-head collisions is set by the impact parameter that controls the resulting shape of aggregates, their anisotropy, and fractal dimension.


Electro-Optic Kerr Effect In Polymer-Stabilized Isotropic Liquid Crystals, Young-Cheol Yang, Deng-Ke Yang Jan 2011

Electro-Optic Kerr Effect In Polymer-Stabilized Isotropic Liquid Crystals, Young-Cheol Yang, Deng-Ke Yang

Chemical Physics Publications

The electro-optic Kerr effect with a high Kerr constant around 10−9 m/V2 was observed in the polymer-stabilized isotropic liquid crystals over a wide temperature range. Optical isotropy at the field-off state was attained with randomly oriented domains of (chiral) nematic liquid crystals formed by a polymer matrix cured in the isotropic phase. Optical birefringence in the field-on state was induced by the reorientation of liquid crystals in the domains. Rapid rising and falling response times of the cells around 0.26 ms (0.52 ms total response time) were achieved. A theoretical model was proposed to explain the ...


The Effect Of Surface Alignment On Analog Control Of Director Rotation In Polarization Stiffened Smc* Devices, Mitya Reznikov, Lena M. Lopatina, Michael J. O'Callaghan, Philip J. Bos Jan 2011

The Effect Of Surface Alignment On Analog Control Of Director Rotation In Polarization Stiffened Smc* Devices, Mitya Reznikov, Lena M. Lopatina, Michael J. O'Callaghan, Philip J. Bos

Chemical Physics Publications

The effect of surface alignment on the achievement of analog ("V"-shaped) electric field control of director rotation in SmC* liquid crystal devices is investigated experimentally and through numerical modeling. Ferroelectric SmC* liquid crystals are intrinsically analog and thresholdless, i.e. the director can be rotated freely around the tilt cone. Whether or not a SmC* liquid crystal cell exhibits thresholdless switching depends strongly on the influence of the cell's alignment layers, on the magnitude of the liquid crystal's spontaneous polarization, and on whether smectic layers adopt a bookshelf or chevron configuration. To study the effect of the ...


Modeling And Simulation Of Liquid-Crystal Elastomers, Wei Zhu, Michael Shelley, Peter Palffy-Muhoray Jan 2011

Modeling And Simulation Of Liquid-Crystal Elastomers, Wei Zhu, Michael Shelley, Peter Palffy-Muhoray

Chemical Physics Publications

We consider a continuum model describing the dynamic behavior of nematic liquid crystal elastomers (LCEs) and implement a numerical scheme to solve the governing equations. In the model, the Helmholtz free energy and Rayleigh dissipation are used, within a Lagrangian framework, to obtain the equations of motion. The free energy consists of both elastic and liquid crystalline contributions, each of which is a function of the material displacement and the orientational order parameter. The model gives dynamics for the material displacement, the scalar order parameter and the nematic director, the latter two of which correspond to the orientational order parameter ...