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Full-Text Articles in Physics

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 ...


Material-Independent Determination Of Anchoring Properties On Rubbed Polyimide Surfaces, Bharat R. Acharya, Jae-Hoon Kim, Satyendra Kumar Dec 1999

Material-Independent Determination Of Anchoring Properties On Rubbed Polyimide Surfaces, Bharat R. Acharya, Jae-Hoon Kim, Satyendra Kumar

Physics Publications

A material-independent method for determining liquid-crystal (LC) anchoring energy on rubbed polyimide (PI) surfaces has been devised. This method exploits the changes in the easy axis of rubbed PI film induced by exposure to linearly polarized UV (LPUV) Light. The distribution of PI chains in a rubbed film is approximated by a Gaussian function and its width determined from the measured rotation of the LC easy axis as a function of exposure time. A quasimicroscopic free energy of the LC-substrate interface is used to model LC anchoring properties. The experimental and calculated values of the azimuthal anchoring energy are in ...


Determination Of Nematic Polar Anchoring From Retardation Versus Voltage Measurements, Yu A. Natishin, R. D. Polak, Sergij V. Shiyanovskii, Oleg Lavrentovich Jul 1999

Determination Of Nematic Polar Anchoring From Retardation Versus Voltage Measurements, Yu A. Natishin, R. D. Polak, Sergij V. Shiyanovskii, Oleg Lavrentovich

Chemical Physics Publications

The popular “high-electric-field” technique to determine the polar anchoring coefficient W of a nematic–substrate interface requires the simultaneous measurement of the capacitance and optical phase retardation of a liquid crystal cell as a function of applied voltage. We develop a generalized model that makes it possible to eliminate the capacitance measurement. The new technique, called the RV (retardation versus voltage) technique, requires only themeasurement of retardation as a function of applied voltage, and allows for the determination ofW by a linear fit over a prescribed voltage window. The technique is not sensitive to uniformity of the cell thickness ...


Observation Of Pattern Evolution During Homeotropic-Focal Conic Transition In Cholesteric Liquid Crystals, Yang-Ming Zhu, Deng-Ke Yang Jun 1999

Observation Of Pattern Evolution During Homeotropic-Focal Conic Transition In Cholesteric Liquid Crystals, Yang-Ming Zhu, Deng-Ke Yang

Chemical Physics Publications

We have observed an interesting pattern evolution of cholesteric liquid crystals during the homeotropic-focal conic transition in a dispersed polymer network. From the electrical field induced homeotropic state, if the field is:reduced to an appropriate bias level focal conics grow at a constant speed, being an open or compact structure depending on the field strength. When the field is increased, these patterns change to ramified structures. We phenomenologically explained the observation.


Pretilt Angle Generation On Photoreactive Polymer Films, H. G. Galabova, David W. Allender, J. Chen Sep 1998

Pretilt Angle Generation On Photoreactive Polymer Films, H. G. Galabova, David W. Allender, J. Chen

Physics Publications

The mechanism of liquid crystal pretilt angle generation on photoreactive polymer films doubly exposed to linearly polarized ultraviolet (uv) light has been investigated. The first exposure for time; tau(1) is normal to the surface, and the film is subsequently irradiated for time tau(2) With obliquely incident uv light with a plane of polarization rotated by 90 degrees with respect to that of the first uv light. The state of the polymer film after two exposures was characterized with a tensor order parameter, which then served as a boundary condition for the surface state of the nematic liquid crystal ...


Phase-Transitions In Finite-Thickness Nematic Liquid-Crystal Films - Planar Anchoring, Natasha Kothekar, David W. Allender, R. M. Hornreich Oct 1995

Phase-Transitions In Finite-Thickness Nematic Liquid-Crystal Films - Planar Anchoring, Natasha Kothekar, David W. Allender, R. M. Hornreich

Physics Publications

Phase transitions in finite-thickness nematogenic materials bounded by two planar surfaces and characterized by identical surface interactions linearly proportional to the order parameter have been studied theoretically by solving the coupled nonlinear Euler-Lagrange equations. The surface interaction was assumed to favor molecular orientation in the surface plane with no rubbed or preferred direction. The related problem of a semi-infinite film having a single surface has been studied previously at temperatures above the bulk nematic-isotropic phase transition point T-NI. For that geometry and physically relevant elastic constants, it was shown that, in addition to the bulk transition, there is a second ...


Finite Molecular Anchoring In The Escaped-Radial Nematic Configuration: A 2-H-Nmr Study, G. P. Crawford, David W. Allender, J. William Doane, M. Vilfan, I. Vilfan Aug 1991

Finite Molecular Anchoring In The Escaped-Radial Nematic Configuration: A 2-H-Nmr Study, G. P. Crawford, David W. Allender, J. William Doane, M. Vilfan, I. Vilfan

Physics Publications

The director-field configuration of a nematic liquid crystal confined to cylindrical cavities of polycarbonate Nuclepore membranes ranging from 0.3 to 0.05-mu-m in radius is determined using deuterium nuclear magnetic resonance (H-2 NMR). Spectral patterns from cavities of radius 0.3-mu-m reveal the escaped-radial configuration with singular point defects, but as the cylinder size is decreased, the elastic energy imposed by the curvature of the confining walls competes with the anchoring energy to tilt the directors away from their preferred perpendicular anchoring direction, preventing the expected transition to the planar-radial configuration. A surface fitting parameter is directly determined by ...


Nematic-Isotropic Phase-Transition In A Liquid-Crystal Droplet, S. Kralj, S. Zumer, David W. Allender Mar 1991

Nematic-Isotropic Phase-Transition In A Liquid-Crystal Droplet, S. Kralj, S. Zumer, David W. Allender

Physics Publications

Possible phases in a nematic liquid crystal confined to a spherical submicrometer droplet embedded in a solid polymer are analyzed in terms of a Landau-de Gennes theory. For a droplet with a radial structure we show that the strength of the nematic-polymer interfacial interaction affects the nematic-paranematic (partially ordered isotropic phase) phase transition and may in addition induce a boundary-layer nematic phase. This boundary layer phase exists only in a narrow (approximately 0.1 K) temperature interval above the nematic phase for a restricted range of interfacial interactions. Also in the radial structure the degree of ordering is suppressed close ...