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Articles 1 - 9 of 9

Full-Text Articles in Physics

Magnetic-Field Induced Isotropic To Nematic Liquid Crystal Phase Transition, T. Ostapenko, D. B. Wiant, Samuel N. Sprunt, Antal Jákli, Jim T. Gleeson Dec 2008

Magnetic-Field Induced Isotropic To Nematic Liquid Crystal Phase Transition, T. Ostapenko, D. B. Wiant, Samuel N. Sprunt, Antal Jákli, Jim T. Gleeson

Chemical Physics Publications

We report on measurements of magnetic-field induced nematic order in the bent-core liquid crystal 4-chlororesorcinol bis[4-(4-n-dodecyloxybenzoyloxy) benzoate]. Using the 31 T solenoid at the National High Magnetic Field Laboratory, we have observed, at temperatures less than 1 degrees above the clearing point, a first-order transition to the nematic phase. The critical magnetic field at which this occurs increases with temperature. We discuss these results within the context of both Maier-Saupe and Landau-de Gennes mean-field models for the nematic-isotropic transition. The implications of possible tetrahedratic order are also discussed. To our knowledge, this is the first observation of such ...


Polar And Nonpolar Orderings In The Electrically Induced Isotropic-Nematic Phase Transition, Mingxia Gu, Sergij V. Shiyanovskii, Oleg Lavrentovich Oct 2008

Polar And Nonpolar Orderings In The Electrically Induced Isotropic-Nematic Phase Transition, Mingxia Gu, Sergij V. Shiyanovskii, Oleg Lavrentovich

Chemical Physics Publications

We study the dynamics of the isotropic-nematic phase transition caused by an applied electric field at the time scales of dielectric relaxation. In the classic Landau-Khalatnikov theory of the phase transition dynamics, the nematic (nonpolar) order parameter is an instantaneous function of the applied field. We demonstrate that, when the field is changing faster than the time of dielectric relaxation, the induced polar order dynamics influences the dynamics of the nonpolar order parameter. We develop a model based on the Langevin equation to describe the simultaneous dynamics of both polar and nonpolar order parameters; the model is supported by experiment.


Colloidal Micromotor In Smectic A Liquid Crystal Driven By Dc Electric Field, Antal Jakli, Bohdan Senyuk, Guangxun Liao, Oleg Lavrentovich Sep 2008

Colloidal Micromotor In Smectic A Liquid Crystal Driven By Dc Electric Field, Antal Jakli, Bohdan Senyuk, Guangxun Liao, Oleg Lavrentovich

Chemical Physics Publications

Converting linear stimulus to rotation has endless examples in virtually all scales of the universe. One of the interesting examples is Quincke rotation, a spinning rotation of a dielectric sphere neutrally buoyant in an isotropic fluid caused by a unidirectional DC electric field. Recently Quincke rotation has been reported in liquid crystalline (LC) phases, and it was noted that spinning triggers a translational motion normal to the electric field and the rotation axis. In this work, we explain the translation of spinning spheres as a result of hydrodynamic interaction with the bounding walls. We also describe a unique orbiting motion ...


Converse Flexoelectric Effect In A Bent-Core Nematic Liquid Crystal, John Harden, R. Teeling, Jim T. Gleeson, Samuel N. Sprunt, Antal Jakli Sep 2008

Converse Flexoelectric Effect In A Bent-Core Nematic Liquid Crystal, John Harden, R. Teeling, Jim T. Gleeson, Samuel N. Sprunt, Antal Jakli

Chemical Physics Publications

Flexoelectricity is a unique property of liquid crystals; it is a linear coupling between electric polarizations and bend and/or splay distortions of the direction of average molecular orientation. Recently it was shown [J. Harden et al., Phys. Rev. Lett. 97, 157802 (2006)] that the bend flexoelectric coefficient in bent-core nematic liquid crystals can be three orders of magnitude higher than the effect with calamitic (rod-shaped) molecular shape. Here we report the converse of the flexoelectric effect: An electric field applied across a bent-core liquid crystal sandwiched between thin flexible substrates produces a director distortion which is manifested as a ...


Monodomain Alignment Of The Smectic-A Liquid Crystalline Phase From The Isotropic Phase, Mitya Reznikov, Bentley Wall, Mark A. Handschy, Philip J. Bos Aug 2008

Monodomain Alignment Of The Smectic-A Liquid Crystalline Phase From The Isotropic Phase, Mitya Reznikov, Bentley Wall, Mark A. Handschy, Philip J. Bos

Chemical Physics Publications

The liquid crystal alignment method described here provides uniform orientation of otherwise difficult-to-align smectic-A liquid crystal materials lacking a nematic phase. The smectic-A phase is grown in the presence of a 10–20 K/mm temperature gradient from an air bubble located within a cell by a photolithographically defined channel in the cell substrates. We obtain uniform layer alignment in millimeter-wide smectic regions at growth rates below about 0.05 μm/s even though there is a tendency for spontaneous nucleation of focal-conic defects at higher growth rates once the width of the smectic-A region exceeds the critical value of ...


Observation Of A Possible Tetrahedratic Phase In A Bent-Core Liquid Crystal, D. B. Wiant, K. Neupane, S. Sharma, Jim T. Gleeson, Samuel N. Sprunt, Antal Jakli, N. Pradhan, G. Iannacchione Jun 2008

Observation Of A Possible Tetrahedratic Phase In A Bent-Core Liquid Crystal, D. B. Wiant, K. Neupane, S. Sharma, Jim T. Gleeson, Samuel N. Sprunt, Antal Jakli, N. Pradhan, G. Iannacchione

Chemical Physics Publications

An experimental study of the heat capacity, mass density, magnetic-field-induced optical birefringence, linewidth and intensity of scattered light, and the viscosities associated with nematic order parameter fluctuations and fluid flow has been performed on an achiral bent-core liquid crystal above its clearing point temperature. The measurements reveal a transition between two optically isotropic phases that is consistent with recent theoretical predictions of a "tetrahedratic" form of orientational order.


Polarity-Dependent Dielectric Torque In Nematic Liquid Crystals, Mingxia Gu, Sergij V. Shiyanovskii, Oleg Lavrentovich Jun 2008

Polarity-Dependent Dielectric Torque In Nematic Liquid Crystals, Mingxia Gu, Sergij V. Shiyanovskii, Oleg Lavrentovich

Chemical Physics Publications

The dielectric dispersion in the uniaxial nematic liquid crystals affects the switching dynamics of the director, as the dielectric torque is determined by not only the present values of the electric field and director but also by their past values. We demonstrate that this “dielectric memory” leads to an unusual contribution to the dielectric torque that is linear in the present field and thus polarity sensitive. This torque can be used to accelerate the “switch-off” phase of director dynamics.


Longitudinal Double-Spin Asymmetry For Inclusive Jet Production In (P)Over-Right-Arrow + (P)Over-Right-Arrow Collisions At Root S=200 Gev, B. I. Abelev, Quan Li, Star Collaboration Jun 2008

Longitudinal Double-Spin Asymmetry For Inclusive Jet Production In (P)Over-Right-Arrow + (P)Over-Right-Arrow Collisions At Root S=200 Gev, B. I. Abelev, Quan Li, Star Collaboration

Chemical Physics Publications

We report a new STAR measurement of the longitudinal double-spin asymmetry A(LL) for inclusive jet production at midrapidity in polarized p+p collisions at a center-of-mass energy of root s = 200 GeV. The data, which cover jet transverse momenta 5 < p(T) < 30 GeV/c, are substantially more precise than previous measurements. They provide significant new constraints on the gluon spin contribution to the nucleon spin through the comparison to predictions derived from one global fit to polarized deep-inelastic scattering measurements. They provide significant new constraints on the gluon spin contribution to the nucleon spin through the comparison to predictions derived from one global fit to polarized deep-inelastic scattering measurements.


Liquid Crystal Optical Phase Plate With A Variable In-Plane Gradient, Lei Shi, Paul F. Mcmanamon, Philip J. Bos Jan 2008

Liquid Crystal Optical Phase Plate With A Variable In-Plane Gradient, Lei Shi, Paul F. Mcmanamon, Philip J. Bos

Chemical Physics Publications

We propose a nematic liquid crystal (LC) optical phase plate, with a large continuous in-plane gradient that is variable, and its application to a beam steering device with high efficiency. The device is a vertically aligned, continuous phase, optical phased array (V-COPA) that uses a negative dielectric anisotropy LC material. High steering efficiency of over 95% is demonstrated by modeling the LC director field and its effect on transmitted light. The period of the V-COPA grating can be varied by adjusting an applied voltage profile, which allows for continuous angular control of the diffraction angle. (C) 2008 American Institute of ...