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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.


Homeotropically Aligning Phase Separated Columnar Structures For Fabrication Of Flexible Electrooptical Devices, Bharat R. Acharya, Hyunchul Choi, Mohan Srinivasarao, Satyendra Kumar Nov 2011

Homeotropically Aligning Phase Separated Columnar Structures For Fabrication Of Flexible Electrooptical Devices, Bharat R. Acharya, Hyunchul Choi, Mohan Srinivasarao, Satyendra Kumar

Physics Publications

A method of achieving homeotropic alignment of liquid crystals(LCs) by ultraviolet light induced phase separation of LC from its mixture with photo-curable pre-polymer is reported. Vertical polymer columns and micro-fibrils developed during the phase separation promote homeotropic alignment of the LC director (i.e., alignment perpendicular to the LC-substrate interface), suitable for devices based on LCs possessing negative dielectricanisotropy. These vertical structures extend between two substrates and permit the fabrication of highly flexible electro-optical devices with high contrast coupled with fast response times. This simple single-step technique eliminates the need for the traditional polymer alignment layer pre-deposited on substrates.


Homeotropically Aligning Phase Separated Columnar Structures For Fabrication Of Flexible Electrooptical Devices, Bharat R. Acharya, Hyunchul Choi, Mohan Srinivasarao, Satyendra Kumar Nov 2011

Homeotropically Aligning Phase Separated Columnar Structures For Fabrication Of Flexible Electrooptical Devices, Bharat R. Acharya, Hyunchul Choi, Mohan Srinivasarao, Satyendra Kumar

Physics Publications

A method of achieving homeotropic alignment of liquid crystals (LCs) by ultraviolet light induced phase separation of LC from its mixture with photo-curable pre-polymer is reported. Vertical polymer columns and micro-fibrils developed during the phase separation promote homeotropic alignment of the LC director (i.e., alignment perpendicular to the LC-substrate interface), suitable for devices based on LCs possessing negative dielectric anisotropy. These vertical structures extend between two substrates and permit the fabrication of highly flexible electro-optical devices with high contrast coupled with fast response times. This simple single-step technique eliminates the need for the traditional polymer alignment layer pre-deposited on ...


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 ...


The Effect Of Trimethylamine On Atmospheric Nucleation Involving H2so4, M. E. Erupe, A. A. Viggiano, Shan-Hu Lee May 2011

The Effect Of Trimethylamine On Atmospheric Nucleation Involving H2so4, M. E. Erupe, A. A. Viggiano, Shan-Hu Lee

Biostatistics, Environmental Health, and Epidemiology Publications

Field observations and quantum chemical calculations have shown that organic amine compounds may be important for new particle formation involving H2SO4. Here, we report laboratory observations that investigate the effect of trimethylamine (TMA) on H2SO4-H2O nucleation made under aerosol precursor concentrations typically found in the lower troposphere ([H2SO4] of 106−107 cm−3; [TMA] of 180–1350 pptv). The threshold [H2SO4] needed to produce the unity J was from 106−107 cm−3 and the slopes of Log J vs. Log ...


Ternary Homogeneous Nucleation Of H2so4, Nh3, And H2o Under Conditions Relevant To The Lower Troposphere, D. R. Benson, J. H. Yu, A. Markovich, Shan-Hu Lee May 2011

Ternary Homogeneous Nucleation Of H2so4, Nh3, And H2o Under Conditions Relevant To The Lower Troposphere, D. R. Benson, J. H. Yu, A. Markovich, Shan-Hu Lee

Biostatistics, Environmental Health, and Epidemiology Publications

Ternary homogeneous nucleation (THN) of H2SO4, NH3 and H2O has been used to explain new particle formation in various atmospheric regions, yet laboratory measurements of THN have failed to reproduce atmospheric observations. Here, we report first laboratory observations of THN made under conditions relevant to the lower troposphere ([H2SO4] of 106–107 cm−3, [NH3] of 0.08–20 ppbv, and a temperature of 288 K). Our observations show that NH3 can enhance atmospheric H2SO4aerosol nucleation and the enhancement factor (EF) in nucleation ...


Maier-Saupe Theory In Four Dimensions, Xiaoyu Zheng, Peter Palffy-Muhoray Apr 2011

Maier-Saupe Theory In Four Dimensions, Xiaoyu Zheng, Peter Palffy-Muhoray

Mathematical Sciences Publications

Maier-Saupe theory is the canonical mean field description of thermotropic nematic liquid crystals. In this paper, we examine the predictions of the theory in four spatial dimensions. Representations of the order parameter tensor and the existence of new phases are discussed. The phase diagram, based on numerical solution of the self-consistent equations and Landau theory, is presented. Orientational order decreases as the number of spatial dimensions is increased.


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.


Direct Observation Of Diffuse Cone Behavior In De Vries Smectic-A And -C Phases Of Organosiloxane Mesogens, Hyungguen Yoon, Dena M. Agra-Kooijman, Khurshid Ayub, Robert P. Lemieux, Satyendra Kumar Feb 2011

Direct Observation Of Diffuse Cone Behavior In De Vries Smectic-A And -C Phases Of Organosiloxane Mesogens, Hyungguen Yoon, Dena M. Agra-Kooijman, Khurshid Ayub, Robert P. Lemieux, Satyendra Kumar

Physics Publications

Simultaneous and direct x-ray measurements of the smectic layer spacing, molecular tilt, and orientational order in the de Vries smectic A (SmA) and C (SmC) phases of two organosiloxane mesogens reveal that (i) the SmC (tilt) order parameter exponent beta = 0.26 +/- 0.01 for 2nd order SmA-SmC transition-in excellent agreement with the tricritical behavior, (ii) the siloxane and hydrocarbon parts of the molecules are segregated and oriented parallel to the director with very different degree of orientational order, and (iii) thermal evolution of the effective molecular length is different in the two phases.


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 ...


Comment On "Raman Scattering Study Of Phase Biaxiality In A Thermotropic Bent-Core Nematic Liquid Crystal'' Reply, Bharat R. Acharya, Hyunchul Choi, Mohan Srinivasarao, Satyendra Kumar Feb 2011

Comment On "Raman Scattering Study Of Phase Biaxiality In A Thermotropic Bent-Core Nematic Liquid Crystal'' Reply, Bharat R. Acharya, Hyunchul Choi, Mohan Srinivasarao, Satyendra Kumar

Physics Publications

No abstract provided.


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 ...


Isoprene Suppression Of New Particle Formation In A Mixed Deciduous Forest, V. P. Kanawade, B. T. Jobson, A. B. Guenther, M. E. Erupe, S. N. Pressley, S. N. Tripathi, Shan-Hu Lee Jan 2011

Isoprene Suppression Of New Particle Formation In A Mixed Deciduous Forest, V. P. Kanawade, B. T. Jobson, A. B. Guenther, M. E. Erupe, S. N. Pressley, S. N. Tripathi, Shan-Hu Lee

Biostatistics, Environmental Health, and Epidemiology Publications

Production of new particles over forests is an important source of cloud condensation nuclei that can affect climate. While such particle formation events have been widely observed, their formation mechanisms over forests are poorly understood. Our observations made in a mixed deciduous forest with large isoprene emissions during the summer displayed a surprisingly rare occurrence of new particle formation (NPF). Typically, NPF events occur around noon but no NPF events were observed during the 5 weeks of measurements. The exceptions were two evening ultrafine particle events. During the day, sulfuric acid concentrations were in the 106 cm−3 range ...


Park Et Al. Reply, M. S. Park, B.-J. Yoon, J. O. Park, Satyendra Kumar, M. Srinivasarao Jan 2011

Park Et Al. Reply, M. S. Park, B.-J. Yoon, J. O. Park, Satyendra Kumar, M. Srinivasarao

Physics Publications

No abstract provided.


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 ...