This study used electrospinning to fabricate a polyvinylidene fluoride (PVDF) piezoelectric nanofiber harvesting device with interdigitated electrode to capture ambient energy. According to d33 mechanical-electric energy conversion mode, the energy harvesting device can be applied on the low frequency ambient vibration and impact abilities for the transformation mechanical energy into electrical energy effectively. First, the PVDF powder was mixed in acetone solution uniformly and the dimethyl sulfoxide (DMSO) was mixed with multi-walled carbon nanotube (MWCNT) to prepare PVDF macromolecular solution. The mixed solution was filled in a metals needle injector and contacted hundreds of voltage. After the PVDF drop in the needle was subjected to high electric field, the drop overcame surface tension of the solution itself, then extremely fine PVDF fiber was formed and spun out. The electrospun was collected orderly using X-Y digital control stage and the linear diameter of electrospun can be controlled easily by adjusting the travelling speed of the stage. In the spinning process, as affected by stretching strain and electric field at the same time, the PVDF piezoelectric fiber resulted in electric polarization and transformed £] piezoelectric crystal phase, in which the dipoles are oriented in the same direction. Furthermore, MWCNT was added to improve the mechanical properties of fiber and increase £] phase, to enhance the tensile strength and piezoelectric property of PVDF fiber effectively. Finally, the photolithography was used to fabricate interdigitated electrodes with 100£gm gap on the flexible PI substrate. The PVDF fibers, with a length and diameter of approximately 1cm and 700-1000nm, were aligned on interdigitated electrodes and packaged with the PI film. In order to increase the conversion efficiency of piezoelectric fiber in d33 mode, the PVDF fibers were repolarized in a high electric field. The results showed that the PVDF fiber energy harvesting device can generate 15mV open-circuit voltage under low frequency vibration of 4Hz and generate above 30mV open-circuit voltage under 6Hz vibrations. As compared with the piezoelectric fiber not repolarized by interdigitated electrode, its output voltage was increased by1- 2 times.

In this dissertation, the molecular behaviors of water/ethanol mixtures of different weight fractions inside Au nanotubes of different radii at steady state were investigated by molecular dynamics simulation. Five weight fractions of water/ethanol (0/100, 100/0, 25/75, 50/50, and 75/25) and three radii of Au nanotubes (13, 22, and 31.1 Å) were considered in order to understand the effects of Au nanotube size and water/ethanol fraction on the structural and dynamical behaviors of the water and ethanol molecules. The density profiles show two shell-like formations inside the Au nanotubes because water molecules prefer to adsorb on the wall of Au nanotube. According to the density distribution, the space inside Au nanotubes can be divided into three regions, those of contact, transition, and bulk regions, in order from the interior wall surface to the nanotube center. The bulk region has a lower local weight fraction compared to the system water/ethanol weight fraction. In addition, the local water/ethanol weight fraction in the contact region is higher than that of the system. When the system water/ethanol weight fraction becomes higher, the local water/ethanol weight fraction also becomes higher. In 25/75, 50/50, and 75/25 weight fraction mixtures, the number of H-bonds per water and per ethanol are different from those of pure 100% water and 100% ethanol in the Au nanotube due to the nanoconfinement effect. Moreover, the distribution of number of H-bonds in regions where there is only one material will be similar to the distribution in the corresponding region of the pure material, whether 100% water or ethanol. In all regions, the probability to form different H-bonds is affected significantly by the local weight fraction of water/ethanol. Three radii of Au nanotubes (13, 22, and 31.1 Å) were considered in order to understand the effects of Au nanotube size and water/ethanol fraction on the structural and dynamical behaviors of the water and ethanol molecules. In the transition and bulk regions, diffusion coefficients for water and ethanol molecules become higher due to the weak interaction with Au atoms. The values of diffusion coefficients for water molecules in the contact regions are much lower than for those in other regions and are similar for different water/ethanol weight fractions due to the strong interaction with Au atoms. When the radius of the Au nanotube becomes larger, the values of local weight fraction inside the larger radius Au nanotube become higher than those inside small radius Au nanotubes because the ratio of water number to the nanotube inner surface area becomes higher. In addition, water inside a larger radius Au nanotube has a shorter water-water hydrogen bond lifetime (H-bond) in the contact region because the smaller curvature causes weaker interaction with Au atoms.

Through past research, it is known that carbon nanotubes have the potential of enhancing the thermal performance of heat transfer fluids. The research is of importance in electronics cooling, defense, space, transportation applications and any other area where small and highly efficient heat transfer systems are needed. However, most of the past work discusses the experimental results by focusing on the effect of varying concentration of carbon nanotubes (CNTs) on the thermal performance of CNT nanofluids. Not much work has been done on studying the effect of processing variables. In the current experimental work, accurate measurements were carried out in an effort to understand the impact of several key variables on laminar flow convective heat transfer. The impact of ultrasonication energy on CNT nanofluids processing, and the corresponding effects on flow and thermal properties were studied in detail. The properties measured were viscosity, thermal conductivity and the convective heat transfer under laminar conditions. Four samples of 1 wt % multi walled carbon nanotubes (MWCNT) aqueous suspensions with different ultrasonication times were prepared for the study. Direct imaging was done using a newly developed wet-TEM technique to assess the dispersion characteristics of CNT nanofluid samples. The results obtained were discussed in the context of the CNT nanofluid preparation by ultrasonication and its indirect effect on each of the properties. It was found that the changes in viscosity and enhancements in thermal conductivity and convective heat transfer are affected by ultrasonication time. The maximum enhancements in thermal conductivity and convective heat transfer were found to be 20 % and 32 %, respectively, in the sample processed for 40 minutes. The thermal conductivity enhancement increased considerably at temperatures greater than 24 °C. The percentage enhancement in convective heat transfer was found to increase with the axial distance in the heat transfer section. Additionally, the suspensions were found to exhibit a shear thinning behavior, which followed the Power Law viscosity model.

Electronic devices, for logical and memory applications, are constructed based on bistable electronic units that can store binary information. Molecular electronics proposes the use of single molecules—with two distinctive states of conductance—as bistable units that can be used to create more complex electronic devices. The conductance of a molecule is strongly influenced by the contacts used to address it. The purpose of this work is to determine the electrical characteristics of several candidate molecular junctions, which are composed of a molecule and contacts. Specifically, we are interested in determining whether binary information, “0” or “1,” can be encoded in the low- and high-conductance states of the molecular junctions. First, we calculate quantum-mechanically the electronic structure of the molecular junction. Second, the continuous electronic states of the contacts, originated from their infinite nature, are obtained by solving the Schrödinger equation with periodic boundary conditions. Last, the electron transport through the molecular junctions is calculated based on a chemical interpretation of the Landauer formalism for coherent transport, which involves the information obtained from the molecule and the contacts. Metal-molecule-metal and metal-molecule-semiconductor junctions are considered. The molecule used is an olygo(phenylene ethynylene) composed of three benzene rings and a nitro group in the middle ring; this molecule is referred hereafter as the nitroOPE molecule. Gold, silicon, and metallic carbon nanotubes are used as contacts to the molecule. Results from the calculations show that the molecular junctions have distinctive states of conductance for different conformational and charge states. High conductance is found in the conformation in which all the benzene rings of the nitroOPE are coplanar. If the middle benzene ring is made perpendicular to the others, low conductance is found. Also, the negatively charged junctions (anion, dianion) show low conductance. Whenever a semiconducting contact is used, a flat region of zero current is found at low bias voltages. The results indicate that the use of Si contacts is possible; however, because of the flat region, the operating point of the devices needs to be moved to higher voltages.

Polymer nanocomposites refer to a broad range of composite materials with polymer acting as the matrix and any material which has at least one dimension in the order of 1 ~ 100 nanometer acting as the filler. Due to unprecedented improvement observed in properties of the nanocomposites, research interest in this area has grown exponentially in recent years. In designing better nano-composites for advanced technological applications some of the major challenges are: understanding the structure-property relationships, interaction and integrity of the two components at the interface, the role of nanofillers in enhancing the properties of the resulting material. In our work, we have utilized first principle calculations, atomistic simulations, coarse-grained modeling and constitutive equations to develop structureproperty relationships for an amorphous aromatic piezoelectric polyimide substituted with nitrile dipole, carbon nanotubes and resulting nanocomposites. We have studied in detail structure-property relationships for carbon nanotubes and (? ?CN)APB/ODPA polyimide. We have developed chemically sound coarse-grained model based on atomic level simulations of the piezoelectric polyimide to address the larger length and time scale phenomena. The challenge of coarse grain model for these polymers is to reproduce electrical properties in addition to the structure and energetics; our model is the first to successfully achieve this goal. We have compared and analyzed atomistic scale simulation results on the nanocomposite with those predicted from micromechanics analysis. Notably, we have investigated the time dependent response of these highly complex polymers, to our best knowledge this is the first of its kind. In particular we have studied the thermal, mechanical and dielectric properties of the polyimide, nanotube and their nanocomposites through multi-scale modeling technique. We expect the results obtained and understanding gained through modeling and simulations may be used in guiding development of new nanocomposites for various advanced future applications. In conclusion we have developed a computational paradigm to rationally develop next generation nano-materials.

The effects of a carbon nanotube (CNT) coating on bubble departure diameter and frequency in pool boiling experiments was investigated and compared to those on a bare silicon wafer. The pool boiling experiments were performed at liquid subcooling of 10 degrees Celsius and 20 degrees Celsius using PF-5060 as the test fluid and at atmospheric pressure. High-speed digital image acquisition techniques were used to perform hydrodynamic measurements. Boiling curves obtained from the experiments showed that the CNT coating enhanced critical heat flux (CHF) by 63% at 10 degrees Celsius subcooling. The CHF condition was not measured for the CNT sample at 20 degrees Celsius subcooling. Boiling incipience superheat for the CNT-coated surface is shown to be much lower than predicted by Hsu's hypothesis. It is proposed that bubble nucleation occurs within irregularities at the surface of the CNT coating. The irregularities could provide larger cavities than are available between individual nanotubes of the CNT coating. Measurements from high-speed imaging showed that the average bubble departing from the CNT coating in the nucleate boiling regime (excluding the much larger bubbles observed near CHF) was about 75% smaller (0.26 mm versus 1.01 mm)and had a departure frequency that was about 70% higher (50.46 Hz versus 30.10 Hz). The reduction in departure diameter is explained as a change in the configuration of the contact line, although further study is required. The increase in frequency is a consequence of the smaller bubbles, which require less time to grow. It is suggested that nucleation site density for the CNT coating must drastically increase to compensate for the smaller departure diameters if the rate of vapor creation is similar to or greater than that of a bare silicon surface.

Samples are from I-Shou university Department of Materials Science and Engineering, Dr. Huy-Zu Cheng¡¦s laboratory, First, using sol-gel method to produce silicon dioxide (SiO2) with iron catalysts, and with chemical vapor deposition (CVD) to produce carbon nanotubes. To operate these instruments, for example X-Ray diffractometry (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) to analyze. The research point is judging the crystallographic orientation relationships between carbon nanotube and catalysts. Using transmission electron microscopy (TEM) to do diffraction patterns with carbon nanotubes and catalysts. From diffraction patterns results, we can decide what catalysts is? And it¡¦s crystallographic relationship. After affirming from diffraction patterns, there are three chemical compositions in the carbon nanotubes, including Fe3C¡B

Titanium dioxide (TiO2), a semiconductor, has been used in many areas like heterogeneous photocatalysis. In the present study, the effect of hydrothermal treatment conditions and the use of carbon nanotubes on the photocatalytic activity of sol-gel synthesized titanium dioxide were examined. The anatase particles were transformed into layered trititanate particles with either nanotube or nanoplate structure by hydrothermal treatment under the alkaline conditions. Post hydrothermal treatment under neutral conditions was also applied and mesoporous particles were transformed into nanostructured, highly crystalline and ordered anatase particles. Photocatalytic activities of hydrothermally treated samples were determined against Escherichia coli under solar irradiation. Results showed that hydrothermal treatment under alkaline conditions improved the photocatalytic activity. However, although being highly crystalline, after post treatment, a limited activity was obtained because of dehydration of active (101) face of anatase. Nevertheless, TiO2&amp / #8217 / s initial inactivation constant rose from 0.6 to 2.9 hr-1 after regeneration of active sites in aqueous medium under solar irradiation. In order to enhance the surface area and improve activity, multi-walled carbon nanotubes were utilized during the synthesis of TiO2. The effect of calcination conditions and presence of sodium, iron and cobalt on the photocatalytic activity were also studied. For these samples, photocatalytic activities were tested with methylene blue solution under UV irradiation. It was observed that the utilization of CNTs enhanced both the surface area and the activity. Compositions with highest CNT content had better activities for their ability to delay charge recombination. While pure TiO2&amp / #8216 / s initial decomposition constant was 0.8 hr-1, with sodium doping the best value of 1.9 hr-1 was achieved.

Carbon nanotubes have received considerable attention since their discovery due to their novel properties. They have potential application areas in physics, chemistry and biology. Arc discharge, laser furnace, chemical vapor deposition and floating catalyst methods are the most commonly used methods to produce carbon nanotubes. Although carbon nanotubes have superior properties compared to other materials, they could not be used widely. The main reasons of this are that continuous and large scale production of carbon nanotubes could not be achieved and impurities have to be removed. To solve these problems more information about formation of carbon nanotubes has to be known. In this study concentration profiles of reactant and byproducts in a cylindrical reactor are investigated during carbon nanotube production. A special probe to collect gas samples along the reactor and samples loops to store the gas samples were designed and constructed. Gas samples were analyzed one by one in GC/MS. Experiments were done with and without catalyst at same experimental conditions. Thus, effects of catalyst on concentration profiles of chemicals were analyzed. To produce carbon nanotubes more acetylene was used compared to amount of acetylene used in pyrolysis. Increasing reaction temperature from 800&deg / C to 875&deg / C caused decomposing more acetylene and producing more carbon nanotubes. It is believed that data accumulation on the reactions involved in the gas phase will lead to large scale production and lower product costs with a large catalyst surface to be produced in the reactor.

Thermal management is a key challenge to improving the performance of microelectronic devices. For many high performance applications, the thermal resistance between chip and heat sink may account for half of the total thermal budget. Chip-level heat dissipation is therefore a critical bottleneck to the development of advanced microelectronics with high junction temperatures. Recently aligned carbon nanotube arrays have been developed as possible next generation thermal interface materials to overcome this thermal limitation, however the thermal physics of these nanoscale interfaces remains unclear. In this thesis, the thermal interface resistance between a carbon nanotube and adjoining carbon, silicon, or copper substrate is investigated through non-equilibrium molecular dynamics simulation. Phonon transmission is calculated using a simplified form of the diffuse mismatch model with direct simulation of the phonon density of states. The results of theory and simulation are reported as a function of temperature in order to estimate the importance of anharmonicity and inelastic scattering. The results of this work provide a better understand of the mechanisms of thermal transport to assist future CNT TIM research and development.