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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

RAS measurements of anisotropy in rubbed polyimide thin film

Ye, Yi-Jhih 27 July 2007 (has links)
Rubbing alignment is widely used in display industry, Rubbing cause anisotropy in rubbed polyimide thin film influence the alignment of Liquid Crystal. The major part of this article is to analyze surface optical anisotropy of rubbed polyimide thin film. RAS signals and surface free energies of rubbed polyimide thin film with different rubbing strength are measured, and relationship between anisotropy of surface and rubbing strength is discussed. The mechanism of alignment can be understood by this work. Reflection Anisotropy Spectroscopy (RAS) has been used in Semiconductor as a tool to monitor crystal growth for many years. RAS is a non-contact and non-destructive measurement method. It only measures the difference of two orthogonal complex reflection signals and optical anisotropy of surface. It¡¦s very sensitive to the anisotropy of surface. In the current studies, RAS has been used to detect surface anisotropy of rubbed polymer. We measured the surface free energy of the rubbed polyimide thin films. It has been found that surface free energy is of anisotropy due to the application of mechanical rubbing to the polymer surface. Pretilt angle influences the alignment of liquid crystals. The molecule orientation of PI surface and anisotropy of rubbed PI surface effect pretilt angle¡CPretilt angles measured by pretilt angle measurement system compare with RAS signals. RAS signals, anisotropy of surface free energies, and pretilt angles are increasing with increasing rubbing strength.

The Self-Assembly of Discotic Liquid Crystals.

Chiang, Cheng-Yan 02 August 2007 (has links)
Discotic liquid crystals (DLCs), which consist of disc-like molecules, are known to be able to form nematic and columnar mesophases through self-assembly. Because of the high electric charge mobility in one-dimension, DLCs are found to have uses in making electronic and photonic devices, such as organic light emitting diode, photovoltaic and molecular wires. In order to achieve better performance of these applications, it is essential to obtain the desired alignment of the DLCs. The purpose of this study is to investigate the stacking of disk-like molecules and to control their alignment. The materials used in the present studies are HDBP-8 and LC10. In this thesis, we will show that the stack of disk-like molecules is strongly influenced by temperature. We will also discuss how the molecules stacking is influenced by surface free energy. The disk-like molecules tend to stack with face-on when the surface free energy of the substrates is high. On a surface with lower surface free energy, molecules tend to stack with edge-up. In the latter part of the research, substrates are specially treated to have different surface free energies, and molecular stack on these substrates is observed.

The Study of Surface Property of Polyimide Liquid Crystal Alignment Thin Films by Means of Reflection Anisotropy Spectroscopy

Hong, Jia-huang 18 August 2010 (has links)
The purpose of this thesis is to study the relation between surface optical anisotropy of polyimide thin film with different rubbing strength and liquid crystal alignment by means of reflection anisotropy spectroscopy (RAS). We discuss the surface properties of rubbed polyimide thin film by measuring the surface roughness, surface free energy and pretilt angle. RAS is a non-contact optical probe of surfaces. It measures the difference in reflectance of normal incidence linearly polarized light between two orthogonal directions in the surface plane, and we can obtain the surface character of sample by analyzing the signals. It is isotropic of polyimide thin film surface without rubbing, and reflection anisotropy (RA) signal is zero. The non-zero RA signal, i.e. anisotropic of surface, is revealed because of rubbed polyimide thin film surface. The RA signal is increasing with an increase in rubbing strength. In the results, we found that the pertilt angle is increasing with a decrease in surface free energy, and discovered the correlation between RA signal strength of characteristic wavelength and pretilt angle of liquid crystal at the rubbed polyimide thin film.

Development of methods to quantify bitumen-aggregate adhesion and loss of adhesion due to water

Bhasin, Amit 17 September 2007 (has links)
Moisture induced damage of hot mix asphalt pavements has a significant economic impact in terms of excessive maintenance and rehabilitation costs. The moisture sensitivity of an asphalt mix depends on the combined effects of material properties, mixture design parameters, loading conditions and environmental factors. Traditional methods to assess moisture sensitivity of asphalt mixes rely on mechanical tests that evaluate the mix as a whole. These methods do not measure material properties and their role in moisture sensitivity of the mix independently. This information is very important to select materials resistant to moisture induced damage, or to modify locally available materials to improve their resistance to moisture damage for economic reasons. The objective of this research is to develop experimental and analytical tools to characterize important material properties that influence the moisture sensitivity of asphalt mixes. Quality of adhesion between the aggregate and bitumen binder in wet and dry conditions plays an important role on the moisture sensitivity of the asphalt mix. A part of this research work was to develop the Wilhelmy plate method and the Universal Sorption Device to measure the surface free energy components of the bitumen and aggregate with adequate precision and accuracy, respectively. Surface energy of these materials was used to identify parameters based on thermodynamics that can quantify their interfacial adhesion and propensity to debond in the presence of water. The thermodynamic parameters were shown to correlate well with the moisture sensitivity of asphalt mixes determined from laboratory tests. Specific surface areas of the aggregates were also used to account for the influence of mechanical interlocking at the micro scale. In some mixes, chemical bonding also contributes to the adhesion between bitumen and aggregate. The use of a micro calorimeter was introduced in this research as a versatile and fast tool to quantify the combined effects of physical and chemical adhesion between these materials.

Fabrication of Spacers for Ferroelectric Liquid Crystal Display Using Photolithographic Technique and A Study of Their Characteristics

Wang, Chun-chi 15 July 2008 (has links)
Surface stabilized ferroelectric liquid crystal device (SSFLCD) has fast response time and exhibits excellent bistability. The SSFLCD has wide view angle because it operates in the in plane switching (IPS) mode. However, SSFLCD is a thin device, the uniform of its cell gap is difficult to control. When surface stabilized ferroelectric liquid crystal align, it is easy to bring in zigzag defect. In this study, the use of SU-8 photoresist to make photospacer by using photolithographic technique is studied. We control the thickness of photospacer at 1.08£gm. By using photospacer, we can get the cell with uniform cell gap. The influence of the property of the alignment layer and photospacer on surface stabilized ferroelectric liquid crystal alignment are discussed. We find that when the liquid crystal is injected anti-parallel to the rubbing direction, the alignment of Surface stabilized ferroelectric liquid crystal is easily influenced by photospacers. Wetting characteristics of the substrates is found to strongly affect the alignment of the ferroelectric liquid crystal.

Modify Surface Charestist to Produce Zigzag-free Surface Stablized Ferroelectric Liquid Crystal Device

Chen, Yi-Jen 08 July 2009 (has links)
In our study, we use mixed polyimide method and different rubbing conditions to modify surface characteristics for producing zigzag-free surface stablized ferroelectric liquid crystal(SSFLC) device. We utilize contact angle measuring system to obtain the surface free energy and also use rotating crystal method to measure the pretilt angle. Finally, we observe optical textures of SSFLC device with polarized optical microscope. In mixed polyimide experiment, we can approximately provide the pretilt angle between 0¢X and 90¢X, and we also demonstrate different pretilt angle is modified by the surface of different surface free energy. In the end of this experiment, we obtain the better optical texture of SSFLC device in 18.3¢X pretilt angle, but part regions of the texture still possess zigzag defects. In different rubbing conditions experiment, when the cumulative number of rub is 2 or 3 times in 0.3mm pile impression, we can produce zigzag-free SSFLC device in different horizontal polyimide alignment materials.

Initial adhesion of EPS producing bacteria Burkholderia cepacia – the impact of cranberry juice

Yang, Xuejiao Unknown Date
No description available.

Initial adhesion of EPS producing bacteria Burkholderia cepacia the impact of cranberry juice

Yang, Xuejiao 11 1900 (has links)
The impact of cranberry juice was investigated with respect to the initial adhesion of three isogenic Burkholderia cepacia bacteria with different extracellular polymeric substance (EPS) producing capacities: a wild-type cepacian EPS producer PC184, mutant bacteria PC184rml with reduced EPS production, and PC184bceK with a deficiency in EPS production. Adhesion experiments demonstrated that in the presence of cranberry juice, the adhesive capacity of PC184 was largely reduced, while cranberry juice had little impact on the adhesion of either mutant. Thermodynamic modeling supported results from adhesion experiments. For PC184, the surface free energy change Gadh switched from negative in the absence of cranberry juice to positive when cranberry juice was added. Surface force apparatus (SFA) and scanning electron microscopy (SEM) studies demonstrated strong adsorption of cranberry juice components to bacterial EPS. It was concluded that cranberry juice components could impact bacterial initial adhesion by adhering to EPS and impairing bacterial adhesive capacity. / Environmental Engineering


JOSEPH, WAEL 11 June 2002 (has links)
No description available.

Functionalisation of polyolefins and its effects on surface chemistry and energetics

Popat, Rohit P. January 1995 (has links)
The surface functionalisation of polyethylene and polypropylene by industrial and laboratory scale corona treatments and by laboratory flame treatment was studied. The surface sensitive techniques of X-ray photoelectron spectroscopy (XPS), attenuated total reflection infra-red spectroscopy (FTIR-ATR), contact angle measurement and electron microscopy (SEM and TEM) were employed. Corona and flame treatments resulted in incorporation of oxygen only into the surfaces of both polyethylene and polypropylene, resulting in improved surface wettabilities. A variety of oxygen functional groups were introduced by the two treatments. The industrial and laboratory scale treatments of both polymers were found to be similar in terms of the oxygen concentrations incorporated and surface wettabilities achieved. The presence of significant amounts of chain scission products were indicated on corona treated surfaces, while only minimal quantities were indicted on flame treated surfaces. This was attributed to their volatilisation during flame treatment. Introduction of sulfur dioxide into the flame and corona regions during treatment resulted in significant improvements in surface wettability. Incorporation of sulfur and nitrogen resulted from the presence of sulfur dioxide. A possible mechanism involving the formation of sulfonic acid groups and ammonium sulfonate groups was suggested. An oxidation depth model developed for use with variable take-off angle XPS showed that significantly deeper oxidation occurred in the presence of sulfur dioxide. Corona treatment was more effective in improving surface wettabilities than flame treatment, this being attributed to heat induced functional group reorientation during flame . treatment for polyethylene and to differences in surface chemistry resulting from the two treatments in the case of polypropylene. The surface wettability of poly ethylene was more readily improved than the surface wettability of polypropylene after all the treatments investigated. A method for estimating functional group concentrations using chemical derivatisation and contact angle measurement was developed. Functional group estimates for flame treated polyethylene were found to be in good agreement with chemical derivatisation used in conjunction with XPS measurements.

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