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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.
311

Synthesis, characterization and manipulation of Carbon nanotubes

Jin, Xu January 1900 (has links)
Carbon nanotubes (CNTs) are advanced materials that have numerous novel and useful properties. Controlling the synthesis and properties of CNTs is the major challenge toward their future applications. This thesis addresses this challenge with several contributions. This thesis begins with the brief introduction of CNTs, including the history of their discovery, their geometric structure, unique properties and potential applications. Then focus is laid on the subsequent three sections: characterization, synthesis, and manipulation of CNTs. Chapter 2 describes three characterization tools: AFM, SEM and Raman, which are commonly used to analyze CNTs and other nanomaterials. They offer both qualitative and quantitative information on many physical properties including size, morphology, surface texture and roughness. Also, they can be used to determine the structure of CNTS. Chapter 3 addresses the synthesis of CNTS, because synthesis is an important and indispensible process to study CNTs experimentally. Specifically, two controllable synthesis techniques are realized, which are capable to produce iron catalyst nanoparticles for single-walled carbon nanotube (SWNT) growth. Iron nanoparicles of different sizes obtained from both wet chemistry and electrodeposition can be used for diameter-controlled synthesis of SWNTs. Following synthesis, two manipulation methods of CNTs are discussed in Chapter 4. Firstly, effort of electrical breakdown of CNTs is introduced. Both SWNTs and MWNTs (Multi-walled carbon nanotubes) are cut using this method. Moreover, SWNT kink is shown using AFM tip manipulation. These two manipulation methods provide us a possibility to fabricate large cavity from a MWNT for our purposes. In the end of this thesis, conclusions on my master work in research field of CNTs are drawn and future research directions are proposed.
312

Surface Functionalization of Graphene-based Materials

Mathkar, Akshay 16 September 2013 (has links)
Graphene-based materials have generated tremendous interest in the past decade. Manipulating their characteristics using wet-chemistry methods holds distinctive value, as it provides a means towards scaling up, while not being limited by yield. The majority of this thesis focuses on the surface functionalization of graphene oxide (GO), which has drawn tremendous attention as a tunable precursor due to its readily chemically manipulable surface and richly functionalized basal plane. Firstly, a room-temperature based method is presented to reduce GO stepwise, with each organic moiety being removed sequentially. Characterization confirms the carbonyl group to be reduced first, while the tertiary alcohol is reduced last, as the optical gap decrease from 3.5 eV down to 1 eV. This provides greater control over GO, which is an inhomogeneous system, and is the first study to elucidate the order of removal of each functional group. In addition to organically manipulating GO, this thesis also reports a chemical methodology to inorganically functionalize GO and tune its wetting characteristics. A chemical method to covalently attach fluorine atoms in the form of tertiary alkyl fluorides is reported, and confirmed by MAS 13C NMR, as two forms of fluorinated graphene oxide (FGO) with varying C/F and C/O ratios are synthesized. Introducing C-F bonds decreases the overall surface free energy, which drastically reduces GO’s wetting behavior, especially in its highly fluorinated form. Ease of solution processing leads to development of sprayable inks that are deposited on a range of porous and non-porous surfaces to impart amphiphobicity. This is the first report that tunes the wetting characteristics of GO. Lastly as a part of a collaboration with ConocoPhillips, another class of carbon nanomaterials - carbon nanotubes (CNTs), have been inorganically functionalized to repel 30 wt% MEA, a critical solvent in CO2 recovery. In addition to improving the solution processability of CNTs, composite, homogeneous solutions are created with polysulfones and polyimides to fabricate CNT-polymer nanocomposites that display contact angles greater than 150o with 30 wt% MEA. This yields materials that are inherently supersolvophobic, instead of simply surface treating polymeric films, while the low density of fluorinated CNTs makes them a better alternative to superhydrophobic polymer materials.
313

Synthesis, characterization and manipulation of Carbon nanotubes

Jin, Xu January 1900 (has links)
Carbon nanotubes (CNTs) are advanced materials that have numerous novel and useful properties. Controlling the synthesis and properties of CNTs is the major challenge toward their future applications. This thesis addresses this challenge with several contributions. This thesis begins with the brief introduction of CNTs, including the history of their discovery, their geometric structure, unique properties and potential applications. Then focus is laid on the subsequent three sections: characterization, synthesis, and manipulation of CNTs. Chapter 2 describes three characterization tools: AFM, SEM and Raman, which are commonly used to analyze CNTs and other nanomaterials. They offer both qualitative and quantitative information on many physical properties including size, morphology, surface texture and roughness. Also, they can be used to determine the structure of CNTS. Chapter 3 addresses the synthesis of CNTS, because synthesis is an important and indispensible process to study CNTs experimentally. Specifically, two controllable synthesis techniques are realized, which are capable to produce iron catalyst nanoparticles for single-walled carbon nanotube (SWNT) growth. Iron nanoparicles of different sizes obtained from both wet chemistry and electrodeposition can be used for diameter-controlled synthesis of SWNTs. Following synthesis, two manipulation methods of CNTs are discussed in Chapter 4. Firstly, effort of electrical breakdown of CNTs is introduced. Both SWNTs and MWNTs (Multi-walled carbon nanotubes) are cut using this method. Moreover, SWNT kink is shown using AFM tip manipulation. These two manipulation methods provide us a possibility to fabricate large cavity from a MWNT for our purposes. In the end of this thesis, conclusions on my master work in research field of CNTs are drawn and future research directions are proposed.
314

An experimental study of the measurement of low concentration hydrogen sulfide in an aqueous solution

Wu, Dongqing 29 September 2006 (has links)
Endogenously generated H2S has been found not just a toxic substance but may play positive roles, such as the neuromodulator and vasorelaxant in the physiological system since 1990s. Then the precise control of the amount of Hydrogen Sulfide in the animal body raises great interests recently. However, the traditional methods for the Hydrogen Sulfide measurement need a large amount of tissue samples and take a complex procedure; it is impossible to develop any in-vivo real-time approach to measure H2S along the avenue of these methods. There is a great significance to develop new methods toward the measurement of Hydrogen Sulfide in in-vivo, real time, non- or less invasive manner with high resolution. One general idea to make the measurement less invasive is to take blood as sample i.e., to measure Hydrogen Sulfide in blood. <p>The study presented in this thesis aimed to conceive of new measurement methods for Hydrogen Sulfide in an aqueous solution along with their experimental verification. Though the blood sample will eventually be taken, the present study focused on an aqueous solution, which is a first step towards the final goal to measure Hydrogen Sulfide in blood. The study conducted a thorough literature review, resulting in the proposal of five methods, including: (i) the Hydrogen Sulfide measurement by Atomic Force Microscopy, (ii) the H2S measurement by Raman spectroscopy directly, (iii) the Hydrogen Sulfide measurement by Gas Chromatography/Mass Spectroscopy directly (with the static headspace technique), (iv) the Hydrogen Sulfide measurement by Mass Spectroscopy with Carbon Nanotubes, and (v) the Hydrogen Sulfide measurement by Raman spectroscopy with Carbon Nanotubes. The experiments for each of these methods were carried out, and the results were analyzed. Consequently, this study shows that method (v) is very promising to measure low concentration Hydrogen Sulfide in an aqueous solution, especially with the concentration level down to 10 μM and the presence of a linear relationship between the Hydrogen Sulfide concentration and its luminescent intensity.
315

The role of RGD-rosette nanotubes in migration and apoptosis of bovine neutrophils

Minh Hong Anh, Le 12 January 2009 (has links)
Bovine respiratory disease complex is the most common disease that causes sig-nificant economic loss, typically in feedlot cattle. Current treatment methods are focused on reducing inflammatory responses, control of airway reactivity and improvement of pulmonary functions without potential side effects. Neutrophils are the key contributors in acute lung inflammation. However, activated neutrophils live longer and cause exces-sive tissue damage upon migration into lungs. Therefore, modulation of their migration and lifespan are attractive approaches in treatment strategies of bovine respiratory dis-ease. Nanotechnology holds significant potential to design new compounds by our ability to manipulate at the nanoscale. Helical rosette nanotubes are a class of novel, biologi-cally inspired, water soluble and metal-free nanotubes. I used helical rosette nanotubes conjugated to arginine-glycine-aspartic acid (RGD-RNT) to study their effects on neu-trophil chemotaxis, cell signaling and apoptosis. Bovine neutrophils exposed to 5% RGD-RNT reduced their migration in response to fMLP (formyl-Methionyl-Leucyl-Phenylalanine), compared to the non-treated group (P<0.001). This inhibitory effect was the same as that of groups treated with ERK1/2 inhibitor (UO126) and p38 MAPK in-hibitor (SB239063). In addition, the phosphorylated ERK1/2 and p38 MAPK for the first time were quantified by sandwich ELISA to elucidate the mechanism of neutrophil mi-gration. The phosphorylation of both the ERK1/2 and p38 was inhibited at 5 minutes by RGD-rosette nanotubes (P<0.05). Furthermore, integrin ÑvÒ3 is possibly involved in mi-gration of bovine neutrophils. Moreover, RGD-RNT did not induce apoptosis of bovine neutrophils which was inversed by pre-exposing them to LPS for 30 minutes (P<0.001). These experiments provide the first evidence that RGD-rosette nanotubes suppress phos-phorylation of ERK1/2 and p38 MAPK and inhibit chemotaxis of bovine neutrophils.
316

Promoted Co-CNT nano-catalyst for green diesel production using Fischer-Tropsch synthesis in a fixed bed reactor

Trepanier, Mariane 20 September 2010 (has links)
This research project is part of a larger Canadian endeavour to evaluate feasibility of using new nanocatalyst formulations for Fischer-Tropsch synthesis (FTS) to convert fossil-derived or renewable gaseous fuels into green diesel. The green diesel is a clean fuel (with no aromatics and sulfur compounds) suitable for the commonly used transportation system. The catalyst investigated is cobalt metal supported on carbon nanotubes (CNTs). The physical properties of CNTs have improved the common cobalt catalyst currently used in industry. Carbon nanotubes have high surface area, a very stable for FTS activity and, contrary to other common supports, do not interact with the catalyst active phase to produce undesirable compounds. Moreover, CNTs differ from graphite in their purity and by their cylindrical form, which increases the metal dispersion and allows confinement of the particles inside the tubes. Thus, carbon nanotubes as a new type of carbon material have shown interesting properties, favoring catalytic activity for FTS cobalt catalyst. Their surface area can be modified from 170 to 214 m^2/g through acid treatment. The CNT support lowers the amount of Ru promoter needed to increase the catalyst activity up to 80 % CO conversion and potassium promoter increases the selectivity for á-olefins. The olefin to paraffin (O/P) ratio for Co/CNT and CoK/CNT are 0.76 and 0.90, respectively. Moreover, the Co-Fe bimetallic catalysts supported on CNT have proved to be much more attractive in terms of alcohol formation, up to 26.3 % for the Co10Fe4/CNT. The structural characteristics of CNTs have shown to be suitable for use as catalytic support materials for FTS using microemulsion preparation method as applied to produce nanoparticle catalysts. Microemulsion technique results show uniform nanoparticle that are easy to reduce. In addition, the confinement of the particles inside the CNT has improved the lifetime of the catalyst by decreasing the rate of sintering. The deactivation rate at high FTS activity is linear (XCO = -0.13 t(hr) + 75) and at low FTS activity is related to a power law expression of order 11.4 for the cobalt particles outside the tubes and 30.2 for the cobalt particles inside the tube. The optimized catalyst studied was the CoRuK/CNT catalyst. The best kinetic model to describe the CoRuK/CNT catalyst is: 18.5 x 10 ^-5 PH2^0.39/ (1 + 7.2 10 ^-2 PCO^0.72 PH2^0.1)^2.
317

Pool boiling studies on nanotextured surfaces under highly subcooled conditions

Sathyamurthi, Vijaykumar 15 May 2009 (has links)
Subcooled pool boiling on nanotextured surfaces is explored in this study. The experiments are performed in an enclosed viewing chamber. Two silicon wafers are coated with Multiwalled Carbon Nanotubes (MWCNT), 9 microns (Type-A) and 25 microns (Type-B) in height. A third bare silicon wafer is used for control experiments. The test fluid is PF-5060, a fluoroinert with a boiling point of 56°C (Manufacturer: 3M Co.). The apparatus is of the constant heat flux type. Pool boiling experiments in nucleate and film boiling regimes are reported in this study. Experiments are carried out under low subcooling (5 °C and 10 °C) and high subcooling conditions (20°C to ~ 38°C). At approximately 38°C, a non-departing bubble configuration is obtained on a bare silicon wafer. Increase in subcooling is found to enhance the critical heat flux (CHF) and the CHF is found to shift towards higher wall superheats. Presence of MWCNT on the test surface led to an enhancement in heat flux. Potential factors responsible for boiling heat transfer enhancement on heater surfaces coated with MWCNT are identified as follows: a. Enhanced surface area or nano - fin effect b. Higher thermal conductivity of MWCNT than the substrate c. Disruption of vapor-liquid vapor interface in film boiling, and of the “microlayer” region in nucleate boiling d. Enhanced transient heat transfer caused by local quasi-periodic transient liquid-solid contacts due to presence of the “hair like” protrusion of the MWCNT e. Enhancement in the size of cold spots f. Pinning of contact line, leading to enhanced surface area underneath the bubble leading to enhanced heat transfer Presence of MWCNT is found to enhance the phase change heat transfer by approximately 400% in nucleate boiling for conditions of low subcooling. The heat transfer enhancement is found to be independent of the height of MWCNT in nucleate boiling regime in the low subcooling cases. About 75%-120% enhancement in heat transfer is observed for surfaces coated with MWCNT under conditions of high subcooling in the nucleate boiling regime. Surfaces coated with Type-B MWCNT show a 75% enhancement in heat transfer in the film boiling regime under conditions of low subcooling.
318

Investigation on the Adsorption Mechanism and Dynamic Behavior of Water Molecules inside Au Nanotubes

Hsieh, Nan-kai 24 July 2007 (has links)
In recent years, the characteristic of Nano fluid channel has important contribute in bio-technology and nano-machine. Gold atoms in all materials have significant effects on human bodies, which have attracted considerable academic interests when applied to biotechnology. Especially the Au nanotubes has combine an excellent bio-compatible not only using in chemical analyzed and chemical inspect, but also has function on transport fluid molecule in micro channel. This study utilizes molecular dynamics to the behavior of water molecules inside Au nanotubes. We used the potential of Spohr, F3C and Tight-binding in different water density and temperature to investigate the adsorption mechanism and dynamic behavior of water molecules inside Au nanotubes. We discuss the numbers of absorbed water molecule near the inner tube wall all achieve to saturation at three different densities, temperature and size of Au nanotubes. This work we compared water density, the percentage profiles of hydrogen bond, orientational order and flux for water molecules inside the Au nanotubes.
319

The Research of Using Scenario Analysis and STP Strategy to Research New Products Entering The Market-Take CNT-FED for Example

Chuang, Fu-Chi 02 July 2003 (has links)
The tendency of using flat panel display (FPD) to be the final receiver of digital information is going to take shape because of the digitization. Besides the traditional cathode ray tube (CRT) display , there are several display products in the FPD market, such as liquid crystal display (LCD) , Plasma Display Panels (PDP), organic light-emitter diode (OLED) and so on. Nowadays, because of the innovation of nanotechnnology, which drove the development of carbon nanotubes field effective display (CNT-FED). This new products driven by technology will confront two questions as follows : (1) The can¡¦t understand the real scale of market. (2) They can¡¦t forecast the time they need to spend to realize the market chance. Therefore , how to modify the new-products-entering model is an worthy problem to research . The research was done by using the ways of interviewing experts and secondary data collection. Then, we used scenario analysis to build the most possible scenario that CNT-FED may encounter in the future. Under the scenario, we used the approachs of STP strategy to develop th model that CNT-FED enters the market in the future.From the conclusion of this research, we know that CNT-FED should choose the market segment of big panel at the first time entering the market, and it will complete with PDP. Because the performance of CNT-FED is much better than PDP , we need to let the customers realizing and identifying this difference. Therefore, we can reduce the weakness of CNT-FED because of its high price , and , then, we can build the niche market of CNT-FED.
320

A continuous impingement mixing process for effective dispersion of nanoparticles in polymers

Ganapathy Subramanian, Santhana Gopinath 30 October 2006 (has links)
Mixing refers to any process that increases the uniformity of composition and is an integral part of polymer processing. The effective mixing of nanoparticles into polymers continues to be one of the leading problems that limit large scale production of polymer nanocomposites. Impingement mixing is a novel, relatively simple, continuous flow mixing process wherein mixing is accomplished by immersing a high velocity jet in a slower co-flowing stream. The resulting recirculating flow produces an energy cascade that provides a wide range of length scales for efficient mixing. An impingement mixing process was developed and studied through experiments and simulations. Numerical simulations were conducted using FLUENT to understand better the mechanism of operation of the mixer. The formation of a recirculation zone was found to affect the dispersion of nanoparticles. Results of the simulations were compared with experimental data obtained under similar conditions. While this process may be used for any polymernanoparticle combination, the primary focus of this study was the dispersion of Single Walled Carbon Nanotubes (SWNTs) in an epoxy matrix. The dispersion of SWNTs was evaluated by analyzing SEM images of the composites. The image analysis technique used the concept of Shannon Entropy to obtain an index of dispersion that was representative of the degree of mixing. This method of obtaining a dispersion index can be applied to any image analysis technique in which the two components that make up the mixture can be clearly distinguished. The mixing process was also used to disperse SWNTs into a limited number of other polymers. The mixing process is an "enabling" process that may be employed for virtually any polymer-nanoparticle combination. This mixing process was shown to be an effective and efficient means of quickly dispersing nanoparticles in polymers.

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