Spelling suggestions: "subject:"liquidcrystal"" "subject:"liquidcrystals""
41 |
Polarization-independent nonlinear effect of dye doped cholesteric liquid crystalsHsu, Ming-chun 01 August 2012 (has links)
In this thesis, the nonlinear properties of dye-doped liquid crystal films measured
via Z-scan technique are presented, and we¡¦ve also compared the features of nonlinear
effect between nematic and cholesteric liquid crystals, because the purpose was to
obtain a strong nonlinear effect which is polarization independent. The nonlinear
refraction of the samples would induce self-focusing/self-defocusing effect, therefore
the Z-scan technique was utilized for the measurements in this study. The degrees of
self-focusing/self-defocusing effect can be used to calculate the optical Kerr constants n2
related to the variation of refractive indices. Moreover, this technique is
uncomplicated and powerful for nonlinear effect observations, because it only requires a
single laser beam and a simple setup to measure both nonlinear refractive indices and
nonlinear absorption coefficients.
In the first section of the study, we had investigated the nonlinear effect of
azo-dye-doped liquid crystal (ADDLC) films by Z-scan technique. Owing to the
birefringence provided by homogeneous-alignment liquid crystal films and the
absorption difference between the long axis and the short axis of the azo dye, the
self-defocusing effect in nematic phase was larger than that in isotropic state as the
polarization of incident light was parallel to the long axis of aligned liquid crystals.
While we set the incident polarization perpendicular to the long axis of liquid crystals, a
self-focusing effect was observed and the in nematic phase was found smaller than
that in isotropic state. As a result, it can be analyzed that the nonlinear effect of
homogeneous aligned ADDLC films is intensely polarization-dependent.
In the second section, in order to acquire a polarization-independent nonlinear
effect, we fabricated the azo-dye-doped cholesteric liquid crystal (ADDCLC) films
which were arranged in planar texture with the reflection bands managed to avoid the III
wavelength of incident light. We had studied the nonlinear effects in different
concentrations of the azo dye and also measured the influence of incident polarizations.
We discover that when the concentration of dyes was raised, the n2 increased as well;
the nonlinear indices were almost the same in various polarized light. The incident light
suffered an average refractive index in an ADDCLC film, and azo dye arranged in
helices resulted in identical absorption to different polarized light. In summary,
employing ADDCLCs with planar texture in nonlinear optical applications, we could
achieve not only strong nonlinear effects but also high polarization independence in
liquid crystals.
|
42 |
Synthesis of New Dibenzo[a,c]phenazine Discotic Liquid Crystal (III)Su, You-lou 25 August 2009 (has links)
In our laboratory, we using simple synthetic methods
to synthesize one series of amphiphilic discotic
liquid crystal which has the dipole-dipole forces.
We not only research the effect about the length of
hydrophilic chain, but also explore the arrangement
of this series through some cross-comparison.
|
43 |
Birefringence, anisotropic shrinkage and luminance in injection molded light-guide plate modeling and experiment /Lin, Tsui-Hsun. January 2009 (has links)
Dissertation (Ph. D.)--University of Akron, Dept. of Polymer Engineering, 2009. / "May, 2009." Title from electronic dissertation title page (viewed 11/27/2009) Advisor, Avraam I. Isayev; Committee members, James L. White, Thein Kyu, Kevin Kreider, Shi-Qing Wang; Department Chair, Sadhan C. Jana; Dean of the College, Stephen Cheng; Dean of the Graduate School, George R. Newkome. Includes bibliographical references.
|
44 |
Bistable twised nematic liquid crystal displays by inhomogeneous alignment surfaces /Lee, Chung Yung. January 2009 (has links)
Includes bibliographical references.
|
45 |
Submillisecond-response Blue Phase Liquid Crystals For Display ApplicationsChen, Kuan Ming 01 January 2012 (has links)
With exploding growth of information exchanges between people, display has become indispensable in our daily lives. After decades of intensive research and development in materials and devices, and massive investment in manufacturing technologies, liquid crystal display (LCD) has overcome various obstacles and achieved the performance we need, such as wide viewing angle, high contrast ratio, and high resolution, etc. These excellent performances make LCD prevailed in every perspective. Recently, with the demands of energy conservation, a greener LCD with lower power consumption is desired. In order to achieve this goal, new energy-effective driving methods, such as field sequential color display, have been proposed. However, in order to suppress color breakup the LC response time should be faster than 1 ms. To overcome this challenge, various fast-response liquid crystal modes, such as thin cell gap, low viscosity materials, overdrive and undershoot voltages, polymer stabilization, and ferroelectric liquid crystal, are under active investigations. Among these approaches, blue phase liquid crystal (BPLC) shows a greater potential with less fabrication limitations. In this dissertation, the feasibility of polymer-stabilized blue phase liquid crystal for display applications is explored starting from the building blocks of the material system, polymer-stabilization processes, test cell preparations, electro-optical (EO) properties, to suggested approaches for further improvements. iv Because of the nature of blue phase liquid crystals, delicate balance among system components is critically important. Besides the properties of each composition, the preparation process also dictates the EO performance of the self-assembled nano-structured BPLC composite. After the preparation of test cells, EO properties for display applications are investigated and results described. Approaches for further improvements of the EO properties are also suggested in the final part of this dissertation.
|
46 |
Fast Response Dual Frequency Liquid Crystal MaterialsSong, Qiong 01 January 2010 (has links)
Dual frequency liquid crystal (DFLC) exhibits a positive dielectric anisotropy at low frequencies and negative dielectric anisotropy at high frequencies. The frequency where dielectric anisotropy is zero is called crossover frequency. DFLC can achieve fast rise time and fast decay time with the assistance of applied voltage. However, one drawback of DFLC is that it has dielectric heating effect when driven at a high frequency. Thus, the first part of this dissertation is to develop low crossover frequency DFLC materials. The dielectric relaxation and physical properties of some single- and double-ester compounds were investigated. Experimental results indicate that the double-ester compound exhibits a ~ 3 X lower dielectric relaxation frequencies and larger dielectric anisotropy than the single ester, but its viscosity is also higher. More generally, ten groups of dual frequency liquid crystals were compared in terms of dielectric relaxation frequency and dielectric anisotropy. The dielectric relaxation theory was discussed at last. To realize fast response time, high birefringence and low viscosity LC are required. From these two aspects, firstly four new high birefringence laterally difluoro phenyl tolane liquid crystals with a negative dielectric anisotropy were studied. These materials are used to enhance the birefringence of DFLC. They have a fairly small heat fusion enthalpy (~3000 cal/mol) which improves their solubility in a host. We dope 10 wt% of each compound into a commercial negative mixture N1 and measured their birefringence, viscoelastic constant and figure of merit. Birefringence varies very little among homologues while viscoelastic constant increases as alkyl chain length increases. Secondly, we studied the effects of six diluters for lowering the viscosity while stabilizing the vertical alignment (VA) of the laterally difluoro terphenyl host mixture at elevated temperatures. The pros and cons of each diluter are analyzed. These lateral difluoro terphenyls exhibit a high birefringence, fairly low viscosity, and modest dielectric anisotropy, but their molecular alignment in a VA cell is gradually deteriorated at elevated temperatures as their concentration increases. As a result, the device contrast ratio is decreased noticeably due to the light leakage through the crossed polarizers. Finally, liquid crystal doped with metallic nanoparticles, such as Pd, Ag, or Ag-Pd, which are protected with ligand molecules, such as nematic liquid crystal were studied. The metal nanoparticles doped LC exhibit a frequency modulation (FM) electro-optical (EO) response in the millisecond to submillisecond range together with the ordinary root-mean-square voltage response.
|
47 |
A study of liquid crystalline systems by deuterium magnetic resonanceShilstone, G. N. January 1986 (has links)
No description available.
|
48 |
A nuclear magnetic resonance study of orientational ordering in thermotropic liquid crystalsSachdev, H. S. January 1987 (has links)
No description available.
|
49 |
The influence of dye solutes on the static and dynamic electro-optic properties of nematic mesophasesHubbard, S. D. January 1986 (has links)
No description available.
|
50 |
Ultrasonic investigations of magnetic field induced textural changes in superfluid '3He-AEastop, A. D. January 1986 (has links)
No description available.
|
Page generated in 0.0477 seconds