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Kent State University

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Full-Text Articles in Physics

Nematic Polar Anchoring Strength Measured By Electric Field Techniques, Yuriy A. Nastishin, R. D. Polak, Sergij V. Shiyanovskii, V. H. Bodnar, Oleg Lavrentovich Oct 1999

Nematic Polar Anchoring Strength Measured By Electric Field Techniques, Yuriy A. Nastishin, R. D. Polak, Sergij V. Shiyanovskii, V. H. Bodnar, Oleg Lavrentovich

Chemical Physics Publications

We analyze the high-electric-field technique designed by Yokoyama and van Sprang [J. Appl. Phys. 57, 4520 (1985)] to determine the polar anchoring coefficient W of a nematic liquid crystal-solid substrate. The technique implies simultaneous measurement of the optical phase retardation and capacitance as functions of the applied voltage well above the threshold of the Frederiks transition. We develop a generalized model that allows for the determination of W for tilted director orientation. Furthermore, the model results in a new high-field technique, (referred to as the RV technique), based on the measurement of retardation versus applied voltage. W is determined from ...


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 ...


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 ...


Measurement Of Polar Anchoring Coefficient For Nematic Cell With High Pretilt Angle, Darius Subacius, V. M. Pergamenshchik, Oleg Lavrentovich Jul 1995

Measurement Of Polar Anchoring Coefficient For Nematic Cell With High Pretilt Angle, Darius Subacius, V. M. Pergamenshchik, Oleg Lavrentovich

Chemical Physics Publications

A method to determine the surface anchoring energy of a nematic liquid crystal is proposed. The technique implies the measurements of optical retardation of a nematic cell as a function of a strength and direction of the applied magnetic field. It enables one to get both pretilt angle α and anchoring coefficient W a in the course of the same experiment. As an example, both parameters (α=10.9° and W a =1.5×10−5 J/m2) are measured at the interface between the nematic 5CB and rubbed polyimide film.


Surface Elastic And Molecular-Anchoring Properties Of Nematic Liquid-Crystals Confined To Cylindrical Cavities, G. P. Crawford, David W. Allender, J. W. Doane Jun 1992

Surface Elastic And Molecular-Anchoring Properties Of Nematic Liquid-Crystals Confined To Cylindrical Cavities, G. P. Crawford, David W. Allender, J. W. Doane

Physics Publications

The measurement of the saddle-splay surface elastic constant K24 in a nematic liquid crystal is reported based on two independent deuterium nuclear-magnetic-resonance (2H-NMR) experiments. Fifty years after the pioneering work of Oseen and Zocher, these measurements were made from observations of nematic director-field configurations and a configuration transition discovered in submicrometer-sized cylindrical cavities of Nuclepore membranes under selected surface preparations and wall curvatures. The experimental difficulties in separating the effect of anchoring energy from surface elastic energy (inherent in small confining volumes) were overcome by a unique use of NMR and the ability to predict stable nematic structures with ...


Determination Of The Liquid-Crystal Surface Elastic-Constant K24, David W. Allender, G. P. Crawford, J. W. Doane Sep 1991

Determination Of The Liquid-Crystal Surface Elastic-Constant K24, David W. Allender, G. P. Crawford, J. W. Doane

Physics Publications

Analysis of the Frank free energy for nematics confined to cylindrical regions indicates that the director pattern is dependent on the surface elastic constant K24 if there is weak normal anchoring and escape along the cylinder axis. Using deuterium nuclear-magnetic-resonance techniques on samples of submicrometer-size cavities in Nuclepore membranes, we report the first measurement of K24.


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 ...