Browsing by Author "LIANG, BJ"

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DIRECTOR-CONFIGURATION DIAGRAM FOR A CLOSED-CYLINDER NEMATIC LIQUID-CRYSTAL
(1992-03-01)
LIANG, BJ
;
CHEN, SH
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交大名義發表
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光電工程學系
;
National Chiao Tung University
This study reports that the director configuration diagram of a closed cylinder of nematic liquid crystal (CC NLC) with normal orientation at the walls may contain four kinds of stable director configurations. Sample cells were prepared by treating all walls of a closed cylindrical cavity with DMOAP (N,N-dimethyl-N-octadecyl-3-aminopropyltrimethoxysilyl-chloride) and then filling with NLC 5CB. The optical patterns of the CC NLCs were observed between crossed linear polarizers. A theory explaining these observations was developed by calculating the spatial distribution of the nematic director fields. The stable director configurations depend not only on the ratio of the splay and bend Frank elastic constant (K11/K33), but also on the aspect ratio of the cylinder. In general, the occurrence of a transformation between the radial and the hyperbolic type is determined by a critical transformation ratio K11/K33; there is also a critical aspect ratio remarking the transformation between the point and the ring structure. The calculations predict that the characteristic lengths of both the radial and the hyperbolic ring structure are nearly invariant with respect to K11/K33 and the aspect ratio of the cylinder.
DISCONTINUOUS RADIAL TO AXIAL TRANSFORMATION OF DIRECTOR CONFIGURATION IN A CYLINDRICAL NEMATIC CAVITY
(1991-11-15)
LIANG, BJ
;
CHEN, SH
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交大名義發表
;
電子物理學系
;
National Chiao Tung University
The optical patterns of a nematic liquid crystal confined to a closed cylindrical cavity are observed through crossed polarizers. This optical pattern exhibits an annular phenomenon when the radius of the cylinder is varied. The minor dependence of the width of the bright annulus on the radius of the cavity is presented. The formation of the disclination ring is numerically studied and found to be the physical mechanism of the annular phenomenon. The characteristic length defined as the distance from the ring defect to the laterally cylindrical boundary is nearly invariant and is characterized to be the width of the bright annulus.
ELECTRIC-FIELD-INDUCED MOLECULAR-REORIENTATION OF A MAGNETICALLY BIASED FERRONEMATIC LIQUID-CRYSTAL FILM
(1989-02-01)
LIANG, BJ
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CHEN, SH
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光電工程研究所
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Institute of EO Enginerring
ELECTRO-OPTICAL EFFECT OF A MAGNETICALLY BIASED FERRONEMATIC LIQUID-CRYSTAL
(1988-09-01)
CHEN, SH
;
LIANG, BJ
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電子物理學系
;
光電工程學系
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Department of Electrophysics
OPTICAL-PATTERN SIMULATIONS FOR CLOSED CYLINDERS OF LIQUID-CRYSTALS
(1993-05-01)
LIANG, BJ
;
WEI, JG
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CHEN, SH
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光電工程學系
;
Department of Photonics
Optical patterns for the polarizing microscope textures of closed cylinders of liquid crystals (CCLCs) are studied by the Jones vector formulation. The simulated director configuration diagram of a CCLC with normal orientation at the walls contains four kinds of stable director configurations. The resulting texture under some approximations depends only on phase shifts. The patterns are characterized by dark brushes that coincide with the directions of the crossed polarizers. Additionally, there are concentric circle fringes. For the ring defect structure, the centre region of the cylinder exhibits a black extinction. However, this is not distinguishable as between the hyperbolic and radial structures for both the point and the ring defect patterns. Comparing the observed patterns with the simulated ones, we find that the dark cross brushes and the centre black extinction of simulated patterns are similar to those that are observed. However, the concentric circle fringes of the observed pattern are not in accordance with the simulated pattern.
STABILITY OF A HEDGEHOG NEMATIC CONFIGURATION IN A SMALL CLOSED CYLINDRICAL CAVITY
(1991-09-02)
CHEN, SH
;
LIANG, BJ
;
交大名義發表
;
光電工程學系
;
National Chiao Tung University
This letter presents a study on the stability of molecular configurations in a small closed nematic liquid-crystal cell. A volume point defect exists at the center of the cell with the molecules anchored perpendicularly to the cavity wall. We show that the transformation of a radial hedgehog to a hyperbolic one should occur when the ratio of splay-to-bend elastic constants becomes larger than a certain value that depends on the cell geometry.