Electronic polymers offer significant advantages towards ubiquitous computing due to their low-cost, flexibility and benign fabrication conditions. In this research, ferroelectric polymers were investigated for usage in non-volatile memory applications. The work is focused on the fabrication and ferroelectricity of Polyvinylidene-trifluoroethylene and Polyamide-11 (Nylon-11) thin films. Polyvinylidene fluoride (PVDF) and its copolymers were the first class of ferroelectric polymers discovered. Although the processes and properties of PVDF and copolymers have been extensively studied, most of the reports have been on polymers in the bulk form. This work focuses on thin films of PVDF-TrFE (75:25) copolymer fabricated by solution spin-casting. Remnant polarization, Pr, of the thin films was measured to be 6 μC/cm 2 with a coercive field, Ec, of 60 MV/m. The thin film properties are highly dependent on the temperature of crystallization and is attributed to the amount of all-trans β-phase and crystallinity. Fatigue, defined as polarization loss with repeated switching, was studied and a model based on space charge formation was proposed as the fatigue mechanism. Space charge formation was proposed to be caused by electrochemical reaction of ions (F-) at electrodes and accumulations of detrapped ions at grain boundaries. Incorporating a F- scavenger and forming small crystallites was both observed to decrease fatigue. Nylon-11 and other odd-nylons are the only other class of polymers that have been reported to exhibit ferroelectric D-E hysteresis. The published work has almost exclusively been reported on melt-quenched and cold-drawn bulk polymers and consequently there is no literature on ferroelectricity in thin film odd-nylons. The present work developed a process for the fabrication of ferroelectric thin films of nylon-11 by spin-casting. Among the solvents tested, only a solution with m-cresol was observed to result in ferroelectricity in spun films and could be correlated to the crystal structure of the films. A polarization response, Pr, of 5μC/cm 2 with a coercive field, Ec, of 50MV/m was observed. The processing conditions and their effect on crystal structure were investigated to achieve optimal polarization response. In conclusion, PVDF-TrFE copolymers were fabricated in thin film form and process conditions developed to improve ferroelectric properties. Nylon-11 thin films were successfully fabricated for the first time with a polarization response equivalent to that in bulk polymers.

High temperature studies of reactive melts can be difficult due to contamination issues associated with process container and measuring apparatus transferring material to the melts. Even minor amounts of contaminants can drastically affect thermophysical properties such as surface tension. To overcome this problem, containerless processing techniques that levitate small samples, preventing contact, can be used. In using levitation techniques, available heterogeneous nucleation sites are reduced allowing molten samples to undercool below their equilibrium melting temperatures. This capability is extremely attractive to quasicrystal research as the quasicrystal structure is similar to icosahedral ordering that forms in undercooled liquids. As the degree of icosahedral ordering changes with undercooling, changes in thermophysical properties should be observed. By measuring thermophysical properties in the undercooled state valuable insight can be gained into what parameters affect icosahedral ordering, ultimately leading to better understanding of quasicrystal formation, and possible process control for manufacturing. The goal of this research is to measure surface tension, viscosity and density of several titanium, zirconium and nickel (TiZrNi) based quasicrystal forming and related alloys. These measurements are performed using containerless processing combined with optical non-contact measuring methods. In addition to these measurements, the Transient Calorimetric Technique used to measure specific heat in electrostatic levitation based containerless processing is assessed. This research is done as part the NASA-funded microgravity flight project Quasicrystalline Undercooled Alloys for Space Investigation (QUASI). These 1-g measurements will be part of a thermophysical property database which will be used to help plan and compare against, microgravity experiments.* *This dissertation is a compound document (contains both a paper copy and a CD as part of the dissertation).

Metal foam is a relatively new and potentially revolutionary material that allows for components to be replaced with elements capable of large energy dissipation, or components to be stiffened with elements which will generate significant supplementary energy dissipation when buckling occurs. Metal foams provide a means to explore reconfiguring steel structures to mitigate cross-section buckling in many cases and dramatically increase energy dissipation in all cases. The microstructure of metal foams consists of solid and void phases. These voids have random shape and size. Therefore, randomness, which is introduced into metal foams during the manufacturing processes, creating more uncertainty in the behavior of metal foams compared to solid steel. Therefore, studying uncertainty in the performance metrics of structures which have metal foams is more crucial than for conventional structures. Therefore, in this study, structural application of metal foams considering material and geometrical uncertainty is presented. This study applies the Sobol’ decomposition of a function of many random variables to different problem in structural mechanics. First, the Sobol’ decomposition itself is reviewed and extended to cover the case in which the input random variables have Gaussian distribution. Then two examples are given for a polynomial function of 3 random variables and the collapse load of a two story frame. In the structural example, the Sobol’ decomposition is used to decompose the variance of the response, the collapse load, into contributions from the individual input variables. This decomposition reveals the relative importance of the individual member yield stresses in determining the collapse load of the frame. In applying the Sobol’ decomposition to this structural problem the following issues are addressed: calculation of the components of the Sobol’ decomposition by Monte Carlo simulation; the effect of input distribution on the Sobol’ decomposition; convergence of estimates of the Sobol’ decomposition with sample size using various sampling schemes; the possibility of model reduction guided by the results of the Sobol’ decomposition. For the rest of the study the different structural applications of metal foam is investigated. In the first application, it is shown that metal foams have the potential to serve as hysteric dampers in the braces of braced building frames. Using metal foams in the structural braces decreases different dynamic responses such as roof drift, base shear and maximum moment in the columns. Optimum metal foam strengths are different for different earthquakes. In order to use metal foam in the structural braces, metal foams need to have stable cyclic response which might be achievable for metal foams with high relative density. The second application is to improve strength and ductility of a steel tube by filling it with steel foam. Steel tube beams and columns are able to provide significant strength for structures. They have an efficient shape with large second moment of inertia which leads to light elements with high bending strength. Steel foams with high strength to weight ratio are used to fill the steel tube to improves its mechanical behavior. The linear eigenvalue and plastic collapse finite element (FE) analysis are performed on steel foam filled tube under pure compression and three point bending simulation. It is shown that foam improves the maximum strength and the ability of energy absorption of the steel tubes significantly. Different configurations with different volume of steel foam and composite behavior are investigated. It is demonstrated that there are some optimum configurations with more efficient behavior. If composite action between steel foam and steel increases, the strength of the element will improve due to the change of the failure mode from local buckling to yielding. Moreover, the Sobol’ decomposition is used to investigate uncertainty in the strength and ductility of the composite tube, including the sensitivity of the strength to input parameters such as the foam density, tube wall thickness, steel properties etc. Monte Carlo simulation is performed on aluminum foam filled tubes under three point bending conditions. The simulation method is nonlinear finite element analysis. Results show that the steel foam properties have a greater effect on ductility of the steel foam filled tube than its strength. Moreover, flexural strength is more sensitive to steel properties than to aluminum foam properties. Finally, the properties of hypothetical structural steel foam C-channels foamed are investigated via simulations. In thin-walled structural members, stability of the walls is the primary driver of structural limit states. Moreover, having a light weight is one of the main advantages of the thin-walled structural members. Therefore, thin-walled structural members made of steel foam exhibit improved strength while maintaining their low weight. Linear eigenvalue, finite strip method (FSM) and plastic collapse FE analysis is used to evaluate the strength and ductility of steel foam C-channels under uniform compression and bending. It is found that replacing steel walls of the C-channel with steel foam walls increases the local buckling resistance and decreases the global buckling resistance of the C-channel. By using the Sobol’ decomposition, an optimum configuration for the variable density steel foam C-channel can be found. For high relative density, replacing solid steel of the lips and flange elements with steel foam increases the buckling strength. On the other hand, for low relative density replacing solid steel of the lips and flange elements with steel foam deceases the buckling strength. Moreover, it is shown that buckling strength of the steel foam C-channel is sensitive to the second order Sobol’ indices. In summary, it is shown in this research that the metal foams have a great potential to improve different types of structural responses, and there are many promising application for metal foam in civil structures.

Nanostructured metal oxide films have many applications in catalysis, microelectronics, microfluidics, photovoltaics and other fields. Since the performance of a device depends greatly on the structure of the material, the development of methodologies that enable prescriptive control of morphology are of great interest. The focus of this work is to control the structure and properties of the nanostructured metal oxide films using novel synthetic schemes in supercritical fluids and to use those films as key building components in alternative energy applications. A supercritical fluid is a substance at a temperature and pressure above its critical point. It typically exhibits gas-like transport properties and liquid-like densities. Supercritical fluid deposition (SFD) utilizes these properties of supercritical CO2 (scCO2) to deposit chemically pure metal, oxides and alloys of metal films. SFD is a chemical vapor deposition (CVD)-like process in the sense that it uses similar metal organic precursors and deposits films at elevated temperatures. Instead of vaporizing or subliming the precursors, they are dissolved in supercritical fluids. SFD has typically shown to exhibit higher precursor concentrations, lower deposition temperatures, conformal deposition of films on high aspect ratio features as compared to CVD. In2 O3, ZnO and SnO2 are attractive materials because they are used in transparent conductors. SFD of these materials were studied and In2 O3 deposition kinetics using tris(2,2,6,6-tetramethyl-3,5-heptanedionato) In (III) as precursor were determined. Growth rate dependence on the deposition temperature and the precursor concentrations were studied and the physicochemical and optical properties of In2 O3 films were characterized. Metal oxide nanochannels that can potentially be used for microfluidics have been fabricated by sequentially performing nanoimprint lithography (NIL) and SFD. NIL was used to pattern photoresist grating on substrates and SFD of TiO2 was performed thereafter. Subsequent calcination of the samples at high temperature of 400 °C revealed TiO2 nanochannels. H2-assisted-codeposition of Pt and cerium oxide using SFD was performed on porous carbon substrates for their use as anodes for direct methanol fuel cells. X-ray photoelectron analysis revealed that Pt was deposited as a pure metal and Ce was deposited as an oxide. Electrochemical analysis of a full cell revealed that an anode prepared with SFD exhibited better performance than that prepared with conventional brush-painting method. The second process that was developed is a direct spray-on technique to rapidly deposit crystalline nanoscale dendritic TiO2 onto a solid surface. This technique employs atomization of precursor solutions in supercritical fluids combined with the plasma thermal spraying. A solution of metal oxide precursor in scCO2 was expanded across a nozzle into the plasma jet where it is converted to metal oxide. We have investigated TiO2 as our model system using titanium tetra isopropoxide (Ttip) as a precursor. The film structure depends on key process variables including precursor concentration, precursor solution flow rate and plasma gun to substrate distance. The high surface area of the deposited films is attractive for applications in photovoltaics and we have fabricated dye-sensitized solar cells using these films.

My PhD work focuses on developing new methods to create the macroscopic patterns in a simple, robust, and versatile way. For macroscopic pattern formation, we first use flow coating as an assembly technique, uniquely balancing two driving forces: (i) evaporative deposition of nonvolatile solutes at a three-phase contact line and (ii) precision movement of a confined meniscus layer. This balance leads to the formation of line-based patterns that range in height and width from nanometers to microns, with lengths greater than centimeters. Moreover, we couple this deposition methodology with functional ligand chemistry on the nanoparticle surface, which allows us to create complex nanoparticle structures. By lifting crosslinked nanoparticle ribbons and ropes, exceptionally intriguing structures emanate from this process. The nanoparticle ribbons and ropes demonstrate a leap forward in nanomaterials fabrication, since the nanoscale properties are embedded within a macroscale object that can be manipulated with conventional methods and engineered into advanced technologies. Using mechanical instability, we fabricate a simple, robust stimuli-responsive surface with periodic structures over a large area based upon osmotically-driven surface wrinkling. Although surface wrinkling has received considerable attention in the scientific literature, only a handful of papers have shown the ability to harness perhaps the greatest potential attribute of surface wrinkles: their active reversible nature. The ability to precisely control surface topographic morphologies in accordance with established scaling relationships opens a wide array of advanced materials applications, which do not rely upon cost-limiting fabrication techniques. Specifically, the surfaces respond to solvent exposure by developing well-defined topographic structures over laterally extensive areas due to osmotically-driven differential strains between a surface layer and underlying soft substrate. The observed wrinkling occurs spontaneously, forming hierarchical morphologies with controlled dimensions, and vanishes upon removal of the solvent driving force. The combined responsiveness and reversibility of wrinkling allow for the realization of functional devices, such as smart windows, smart microlens arrays, reversible channels in microfluidic devices. Moreover, by using thermal and osmotic approaches, we study the influence of geometry and material properties on surface instability such as cracking and wrinkling in a trilayer system consisting of a thin film on a soft foundation supported by a rigid substrate.

A comprehensive review was made of the design and construction of flexible metal and rigid reinforced concrete large-span culverts, past documented field experience of monitored culvert performance, and culvert failures. Full-scale field testing of a flexible metal and a reinforced concrete large-span culvert was conducted and the results compared with finite element computer analyses. Based on this work recommendations for improved design and construction of large-span culverts were developed. The review of metal culvert design and construction practice revealed numerous differences among current methods as well as deficiencies. Proposed design limit states were identified and discussed for improved practice. An improved earth load thrust prediction model was developed based on past analytical work considering the flexural rigidity of the structure relative to the surrounding soil, in addition to other factors. The design curves for arching factors were extended to cover a wider range of structural backfill width conditions and shallower burial. Also, a proposed construction procedure was outlined to control construction moments based on deflection limits as a function of the expected level of construction control. None of the existing methods explicitly deals with large-span reinforced concrete culvert design and construction practice. Therefore, a proposed design approach for these culverts was outlined. Construction practice was based on recommendations from the manufacturers. The review of failure cases showed that most failures of large-span metal culverts occurred as a result of poor backfill procedures and/or poor backfill material selection. Other causes were excessive construction loads and invert uplift. Excessive deformation was the most common limit state reached before or at failure. Furthermore, significant variations in structural response may occur over time after construction. Therefore, better construction provisions and control are needed, coupled with consideration of flexural stiffness and moment capacity in design. The field tests showed significant differences in structural behavior between backfilling and live load testing. The metal structure was successfully subjected to very heavy live loads at shallow cover conditions without the use of thrust beams or ribs (current practice). Finite element computer analyses of the two tests showed that earth load responses could be reasonably modeled; however, live load predictions were poor.

Interfacial cracks in bimaterial and sandwich specimens in 4-point flexure were analyzed using the finite element method. The energy release rate(G) and the loading phase angle($\Psi$)were calculated in a variety of bimaterial and sandwich specimens. In the sandwich specimens, different crack configurations were analyzed. For sandwich specimens with fully formed cracks on both interface #s 1 and 2, the analysis predicted crack arrest on interface #1 and growth on interface #2. This phenomenon was observed in previous studies with glass/epoxy/glass sandwich specimens. The analysis also showed that the G value for the crack on interface #2 can be calculated by multiplying the G value for a crack on interface #1 by an appropriate correction factor. This correction factor depends on whether the precrack penetrated the epoxy layer or was arrested at interface #1. The loading phase angle for the crack on interface #2 was found to be greater when the precrack penetrated the intermediate layer than when it was arrested at interface #1. Subcritical crack growth and fracture energy(G$\sb{\rm c})$ measurements were made on glass/PMMA and glass/epoxy/PMMA specimens under high humidity. Threshold values for subcritical crack growth and G,values were lowest for the glass/PMMA interface and highest for the epoxy/PMMA interface with the precrack penetrating the epoxy layer. The Van der Waals bonds between glass and PMMA appear to be weaker than those between epoxy and PMMA. For a crack at the epoxy/PMMA interface in the glass/epoxy/PMMA sandwich specimen, threshold values for subcritical crack growth and G$\sb{\rm c}$ values were lower when the precrack was arrestedon interface #1 than when it penetrated the epoxy layer. The lower phase angle ($\Psi = 5\sp\circ)$ for the crack on interface #2 with the precrack arrested at interface #1 results in a large opening mode stress state on interface #2 which facilitates subcritical crack growth at lower threshold values and also lower G$\sb{\rm c}$ values as compared to the case when the precrack penetrates the epoxy layer and grows along interface #2($\Psi = 66\sp\circ).$

Unlike most other porous materials, which have broad pore size distributions and poorly defined pores, microporous and mesoporous molecular sieve materials are frameworks with pores of well-defined size and geometry. The pore diameters are tunable and are of molecular dimensions allowing the materials to exclude molecules based on size and shape. As a result, powders of both microporous and mesoporous molecular sieves have found applications in catalysis and selective adsorption. Many new and potentially beneficial applications would be possible if thin films of these materials could be synthesized with a desired orientation of the pore structure. Previously, mesoporous silica films had been grown only with the pores parallel to the substrate. In order to achieve directional control of the pores, we synthesized mesoporous silica films in externally applied fields. Growth in shear flow fields gave the best results. However, this technique is limited to imparting directional orientation to channels, which remain in the plane of the substrate. We have utilized this method of channel orientation in an attempt to form mesoporous membranes by depositing mesostructured precursors in the pores of a macroporous substrate. Also, we have researched the structure of a new microporous titanosilicate molecular sieve, designated ETS-4. Thermally treated samples of this material have been shown to be nitrogen selective for methane/nitrogen mixtures. By using the methods of Fourier synthesis recycling and Rietveld refinement of x-ray and neutron diffraction data, we have revealed the shifting of cation positions and a lattice contraction of the structure during heating. Microporous and mesoporous materials are formed from the bottom-up and have pores that are of dimensions unattainable with topdown lithographic techniques. As a result, the pores of these materials give us the potential to template the growth of materials on the nanometer length scale. In order to evaluate their potential application in thermoelectric devices, we have modeled the thermoelectric transport properties of composite films using the semi-classical theory of electron transport. Our results suggest that oriented microporous and mesoporous films would make excellent hosts for nanowires and may yield thermoelectric devices with efficiencies a factor of 4 higher than current materials.

The fracture behavior of 2-D SiC/SiC woven composite was investigated at both ambient and elevated temperatures in this research. At ambient temperature, the fracture initiation toughness and R-curve behavior for composite were characterized and related to in-situ microscopic obseniations of damage accumulation and crack advance. Matrix cracking, crack deflection and branching were observed and dominated fracture behavior in the early loading stage. The key to toughening appeared to be associated with the mechanics of crack arrest at fiber bundles in the woven architecture. After the primary crack extension, the composite behaved non-linearly and a J-integral technique was applied to investigate the R-curve behavior. Substantial fibrous pull-out was observed in this regime of crack advance. An insight into the origin of the $J\sb{R}$-curve of a SiC/SiC woven composite was obtained by experimental characterization of the closure stress-crack opening displacement, $\sigma(u)$, relationship in the process zone of the crack. Application of a previously derived theoretical function, $\sigma\sb{b}(u)$, solely based on fiber bridging, showed consistent results with experimental data. The slow crack growth (SCG) behaviors of three different 2-D SiC/SiC composites were investigated at elevated temperatures from 700$\sp\circ$C to 1200$\sp\circ$C. In Dupont composite, crack length was measured in-situ at temperatures by an optical telescope allowing crack growth rate, V, as a function of applied stress intensity, K, to be obtained directly. Catastrophic failure followed after a limited crack extension suggesting limited SCG behavior at the intermediate temperatures. In contrast, an extensive SCG behavior was observed at 1200$\sp\circ$C. Microstructure observation indicated that crack bridging was absent at the intermediate temperatures but was present at 1200$\sp\circ$C. These results were consistent with the role of temperature on the oxidation and mechanical properties of the fiber bundles. In Goodrich composite, an introduction of boron as well as an increase of carbon interface thickness were found to enhance the time dependent deformation at the crack frontal region. Consequently, instead of the stress intensity factor, K, the energy rate C parameter exhibited a better correlation with the crack velocity.

The effects of shear flow on the phase behavior of a miscible blend of polystyrene with poly(vinyl methyl ether) have been investigated by a combination of fluorescence and rheometry. For this purpose, a Rheometrics RMS-800 rheometer was modified for stress and in-situ fluorescence measurements under well-controlled temperature and deformation conditions. Following equilibration at approximately 25 K below the coexistence temperature, slow heating to temperatures in the two-phase region shows that shearing at a constant rate increases the apparent coexistence temperature. Within the experimental error, the elevation above the quiescent spinodal temperature is related to the shear rate as $\Delta T/T\sb{s}$ = (0.015 $\pm$ 0.002)$\sbsp{\gamma}{\cdot 0.59 \pm 0.04}$; this correlation is independent of the composition in the range of 20-60% (w/w) polystyrene. A shear-induced demixing also occurs in the same blend at temperatures as much as 40 K below the LCST. There appears to be no threshold value of the shear rate or the shear stress for the onset of demixing, but a certain value of rate of work done on the sample roughly describes the onset of demixing at a fixed temperature. When shear does induce demixing, the fluorescence intensity remains much higher than that of the quiescent blend for as long as 24 hours, showing that the segregated phase structures can be stable under shear. However, in other cases, a demixing appears for a shorter time, along with relatively high stresses, shortly after the inception of shear but disappears as the stresses drop at longer times. Transmission electron microscopy on sheared samples confirms the presence of a shear-induced structure. The influence of phase separation on the linear viscoelastic behavior was also studied by measuring the complex moduli $G\sp\prime$ and $G\sp{\prime\prime}$ of the blend at temperatures between 25 and 155$\sp\circ$C. For the 20/80 and 40/60 PS/PVME blends, the terminal zone was in the accessible frequency window and phase separation was accompanied with a large increase in G$\sp\prime$ and $G\sp{\prime\prime}$. In contrast, the complex modulus of the 60/40 PS/PVME blend could not be measured near the terminal zone and the G$\sp\prime$ and G$\sp{\prime\prime}$ did not exhibit any significant changes near the phase transition temperature.