Ultrafiltration (UF) processes are often used as pretreatment before more retentive/costly processes, such as nanofiltration and reverse osmosis. This study shows the results of low-biofouling nanocomposite membranes, loaded with casein-coated silver nanoparticles (casein-Ag-NPs). Membranes were cast and imbedded with Ag-NPs using two approaches, physical blending of Ag-NPs in the dope solution (PAg-NP/CA membranes) and chemical attachment of Ag-NPs to cast membranes (CAg-NP/CA membranes), to determine their biofouling control properties. The functionalization of Ag-NPs onto the CA membranes was achieved via attachment with functionalized thiol groups with the use of glycidyl methacrylate (GMA) and cysteamine chemistries. The immobilization chemistry successfully prevented leaching of silver nanoparticles during cross-flow studies. Pseudomonas fluorescens Migula in brackish water was used for short-term dead-end filtration, where CA and CAg-NP/CA membranes displayed lower flux declines as compared to PAg-NP/CA membranes. In subsequent long-term biofouling studies, also with Pseudomonas fluorescens Migula in brackish water with addition of sodium acetate, chemically-attached Ag-NPs led to a significant reduction in the accumulation of bacterial cells, likely due to the more dispersed nanoparticles across the surface. Therefore, a method was developed to chemically immobilize Ag-NPs to membranes without losing Ag-NP’s antimicrobial properties.

Advances in biomaterials have enabled medical practitioners to replace diseased body parts or to assist in the healing process. In situations where a permanent biomaterial implant is used for a temporary application, additional surgeries are required to remove these implants once the healing process is complete, which increases medical costs and patient morbidity. Bio-absorbable materials dissolve and are metabolized by the body after the healing process is complete thereby negating additional surgeries for removal of implants. Magnesium alloys as novel bio-absorbable biomaterials, have attracted great attention recently because of their good mechanical properties, biocompatibility and corrosion rate in physiological environments. However, usage of Mg as biodegradable implant has been limited by its poor corrosion resistance in the physiological solutions. An optimal biodegradable implant must initially have slow degradation to ensure total mechanical integrity then degrade over time as the tissue heals. The current research focuses on surface modification of Mg alloy (MZC) by surface treatment and polymer coating in an effort to enhance the corrosion rate and biocompatibility. It is envisaged that the results obtained from this investigation would provide the academic community with insights for the utilization of bio-absorbable implants particularly for patients suffering from atherosclerosis. The alloying elements used in this study are zinc and calcium both of which are essential minerals in the human metabolic and healing processes. A hydrophobic biodegradable co-polymer, polyglycolic-co-caprolactone (PGCL), was used to coat the surface treated MZC to retard the initial degradation rate. Two surface treatments were selected: (a) acid etching and (b) anodization to produce different surface morphologies, roughness, surface energy, chemistry and hydrophobicity that are pivotal for PGCL adhesion onto the MZC. Additionally, analyses of biodegradation, biocompatibility, and mechanical integrity were performed in order to investigate the optimum surface modification process, suitable for biomaterial implants. The study concluded that anodization created better adhesion between the MZC and PGCL coating. Furthermore, PGCL coated anodized MZC exhibited lower corrosion rate, good mechanical integrity, and better biocompatibility as compared with acid etched.

The purpose of this study was to examine the performance of several generic types of organic protective coatings as a corrosion protection method for the interior of subsea pipelines in sour gas media. The sour gas environment was simulated in the laboratory by the use of an Autoclave and the performance of the organic coatings was studied via the use of Electrochemical Impedance Spectroscopy (EIS) and Linear Polarization Resistance (LPR) tests to determine the coatings resistance, capacitance and corrosion behavior before and after the exposure to sour gas environment. The coating degradation and the corrosion products formed were examined by the use of SEM/EDS. The results indicated that both FBE and Novolac Epoxy coatings had excellent adhesion properties and chemical resistance. The Amine-Cured Novolac Epoxy coating exhibited good adhesion properties and chemical resistance. However, the Phenolic Epoxy coating started to degrade over time and corrosion took place under the coating.

3D printing is a revolutionary manufacturing method that allows the productions of engineering parts almost directly from modeling software on a computer. With 3D printing technology, future manufacturing could become vastly efficient. However, it is observed that the procedures used in 3D printing differ substantially among the printers and from those used in conventional manufacturing. In this thesis, the mechanical properties of engineering products fabricated by 3D printing were comprehensively evaluated and then compared with those made by conventional manufacturing. Three open-source 3D printers, i.e., the Flash Forge Dreamer, the Tevo Tornado, and the Prusa, were used to fabricate the identical parts out of the same material (acrylonitrile butadiene styrene). The parts were printed at various positions on the printer platforms and then tested in bending. Results indicate that there exist substantial differences in mechanical responses among the parts by different 3D printers. Specimens from the Prusa printer exhibit the best elastic properties while specimens from the Flash Forge printer exhibit the greatest post-yield responses. There further exist noticeable variations in mechanical properties among the parts that were fabricated by the same printer. Depending on the positions that the parts were placed on a printer platform, the properties of resultant parts can vary greatly. For comparison, identical parts were fabricated using a conventional manufacturing method, i.e., compression molding. Results show that compression molded parts exhibit more robust and more homogeneous properties than those from 3D printing. During 3D printing, the machine code (e.g., the Gcode) would provide the processing instructions (the x, y, and z coordinates and the linear movements) to the printer head to construct the physical parts. Often times the default processing instructions used by commercial 3D printers may not yield the optimal mechanical properties of the parts. In the second part of this thesis, the orientation-dependent properties of 3D printed parts were examined. The multi-layered composite theory was used to design the directions of printing so that the properties of 3D printed objects can be optimized. Such method can potentially be used to design and optimize the 3D printing of complex engineering products. In the last part of this thesis, the printing process of an actual automobile A-pillar structure was designed and optimized. The finite element software (ANSYS) was used to design and optimize the filament orientations of the A-pillar. Actual parts from the proposed designs were fabricated using 3D printer and then tested. Consistent results have been observed between computational designs and experimental testing. It is recommended that the filament orientations in 3D-printing be “designed” or “tailored” by using laminate composite theory. The method would allow 3D printers to produce parts with optimal microstructure and mechanical properties to better satisfy the specific needs.

Ceramic manufacturing is an expensive process with long lead times between the initial design and final manufactured part. This limits the use of ceramic as a viable material unless there is a large project budget or high production volume associated with the part. Ceramic stereolithography is an alternative to producing low cost parts through the mixing of a photo curable resin and ceramic particles. This is an additive manufacturing process in which each layer is built upon the previous to produce a green body that can be sintered for a fully dense ceramic part. This thesis introduces a new approach to ceramic stereolithography with a top mask projection light source which is much more economical compared to current vector scanning methods. The research goes through the design and development of a stereolithography printer prototype capable of handling ceramics and the testing of different mixtures to provide the best printing results with varying viscosities. The initial testing of this printer has created a starting point for top mask projection as an economical alternative to current ceramic manufacturing techniques.

Microfluidics refers to manipulation, precise control, and behavior of fluids at the micro and nanoliter scales. It has entered the realm of science as a way to precisely measure or mix small amounts of fluid to perform highly controlled reactions. Glass and polydimethylsiloxane (PDMS) are common materials used to create microfluidic devices; however, glass is difficult to process and PDMS is relatively hydrophobic. In this study, SU-8, an epoxy based (negative) photoresist was used to create various electrokinetic microfluidic chips. SU-8 is commonly used in microelectromechanical design. Spin coating of various SU-8 formulations allows for 1 μm to 100 μm thick layers with aspect ratios reportedly as high as 50:1. Case studies were performed to understand the curing/crosslinking process of SU-8 by differential scanning calorimetry. Supplier (MicroChem) recommended parameters were then altered to allow for adequate development of microfluidic channels, while maintaining enough molecular mobility to subsequently bond the SU-8 to a secondary substrate. Three SU-8 layers were used to create fully (SU-8) enclosed microfluidic channels. An (1) SU-8 2050 fully cured base layer was used as a platform on silicon to build from, (2) an SU-8 2050 partially cured layer for developing microfluidic channels , and (3) an SU-8 2007 uncured layer for bonding a secondary substrate to enclose the microfluidic channels. Bond quality was verified by optical and scanning electron microscopy, which resulted in a nearly 100% bond with little to no reflow of SU-8 into channels. Working pressures (ΔP across the capillary) of 15.57 lb/in2 (max detection) were obtained with no fluid leaks. Electroosmotic flow and steaming potential measurements failed. Electrophoretic behavior of glass particles was observed and particle velocities were compared by the application of 200 volts and 300 volts, across a channel length of 2 cm. Particle velocities obtained ranged from 100 μm/s to 1500 μm/s.

Water soluble conjugated polyelectrolytes (CPEs), which fall under the category of conductive polymers, possess numerous advantages over other conductive materials for the fabrication of electronic devices. Namely, the processing of water soluble conjugated polyelectrolytes into thin film electronic devices is much less costly as compared to the processing of inorganic materials. Moreover, the handling of conjugated polyelectrolytes can be performed in a much more environmentally friendly manner than in the processing of other conjugated polymers because conjugated polyelectrolytes are water soluble, whereas other polymers will only dissolve in toxic organic solvents. The processing of electronic devices containing inorganic constituents such as copper indium gallium selenide (CIGS), is much more expensive and poses much greater environmental risks because toxic metals may be released into landfills or waterways upon cell disposal.75 Because conjugated polyelectrolytes enjoy an assortment of advantages over other materials for the manufacturing of thin film electronic devices, there is globally vested interest in the researching of their properties. Despite the fact that CPEs can serve as efficient electron transport mediums, devices such as organic solar cells cannot realize their highest efficiencies unless the morphology of CPEs is precisely controlled. Charged surfactants can electrostatically and ionically interact with CPEs, and when introduced in specific concentrations, molar ratios, and temperature ranges, will aid in a ‘coil to rod’ transition of the CPE, wherein polymer chains undergo intramolecular transitions to obtain rigid-rod morphologies. The kinetics and thermodynamics of the ‘coil to rod’ transition are heavily dependent upon the type(s) of charged surfactant complexed with the CPE (i.e. on the surfactant architecture). By performing UV/Vis Spectroscopy and Fluorometry on dilute polymer/surfactant solutions, Polarized Optical Microscopy (POM) and Small Angle X-Ray Scattering (SAXS) on high concentration polymer/surfactant solutions, and Differential Scanning Calorimetry (DSC) and X-Ray Diffraction (XRD) on solid-state polymer/surfactant samples, the role of various surfactant architectures on the kinetics and thermodynamics of the ‘coil to rod’ transition was studied. The liquid crystalline physical properties and the extent of solid state crystallinity were also investigated. Through an analysis of the data obtained from these various techniques, it was found that the ‘coil to rod’ transition is progressively favored when the alkyl chain length of a single tailed surfactant is sequentially increased, and that as the concentration of double-tailed surfactant increases, the ‘coil to rod’ transition is negated.

Model glassy polymers, polymethyl methacrylate (PMMA) and polycarbonate (PC) are used to experimentally probe several aspects of polymer fracture. In Chapter 1, the method of pre-stress is employed as a means of improving the fracture properites of brittle PMMA. Samples are tested under equi-biaxial compression, simple shear and a combination of biaxial compression and shear. Equi-biaxial compression is shown to increase the threshold stress level for projectile penetration whereas shear pre-stress has a large effect on the overall energy absorbed during an impact. There is also an apparent interaction observed between compression and shear to dramatically increase the threshold stress. Pre-stressed laminates of PMMA and PC show an increase in damage area because of the unique formation of a secondary cone. In Chapter 2, the effect of stress state on stress relaxation in PMMA and PC is investigated. Direct comparisons are made between uniaxial and biaxial loading conditions. The experimental methods used highlight the effect of hydrostatic stress on the relaxation process. The data shows an increase in relaxation time and increase in the breadth of the relaxation spectrum with increases in hydrostatic stress. This suggests that the stress state can have a significant effect on the useful lifetime of pre-stressed articles. In Chapter 3, Mode I and II fracture studies are performed from quasi-static to low velocity impact rates on PMMA and PC. Mode II testing utilizes an angled double-edge notched specimen loaded in compression. The shear banding response of PMMA is shown to be highly sensitive to rate, with diffuse shear bands forming at low rates and sharp distinct shear bands forming at high rates. As the rate increases, shear deformation becomes more localized to the point where Mode II fracture occurs. PC is much less rate dependent and stable shear band propagation is observed over the range of rates studied with lesser amounts of localization. A new theory is formulated relating orientation in a shear band to intrinsic material properties obtained from true-stress true-strain tests. In a qualitative sense the theory predicts the high rate sensitivity of PMMA. A kinematic limit for orientation within a shear band is also derived based on entanglement network parameters. Mode II fracture in PMMA is shown to occur at this kinematic limit. For the case of PC, the maximum impact rates were not high enough to reach the kinematic limit. In Chapter 4, the deformation response, as observed in a shear band is interpreted through the characterization of the "intrinsic material properties" obtained from true stress - true strain 8compression tests. The relatively high rate sensitivity of PMMA deformed at room temperature is related to the proximity of the beta transition to the test temperature. This is also shown in corollary experiments on PC where deformation near the beta transition is accompanied by an increase in rate sensitivity. Physical aging results in a more narrow alpha transition and is shown to increase strain localization and decrease rate sensitivity at low strain rates.

When a solid, ductile particle impacts a substrate at sufficient velocity, the resulting heat, pressure, and plastic deformation can produce bonding at the interface. The use of a supersonic gas flow to accelerate such particles is known as Cold Spray deposition. The Cold Spray process has been commercialized for some metallic materials, but further research is required to unlock the exciting material properties possible with polymeric compounds. In this work, a combined computational and experimental study a) simulated and optimized the nozzle flow conditions necessary to produce bonding in a polyethylene particle, b) developed and fabricated an experimental device, and c) explored temperature-pressure space across a range of substrate materials, resolving a material dependent ‘window of deposition’ where successful coatings form. Insights into bonding mechanisms are discussed, and paths forward proposed.

Ion sensitive field effect transistors (ISFETs) are semiconductor sensors that have the capability to determine the selected concentration of a specific ion in a solution. Most modern ISFETs utilize their ion selective properties for glucose monitors for diabetics. However, in this thesis, the ISFET fabricated is for the selective detection of K+. The goals of this thesis are to develop a functioning ion-selective polymer membrane, manufacture a working FET device, and implement the two aspects together into a working bench-top K+ selective ISFET device. Properties of a polymer composed of 33 wt.% polyvinyl chloride (PVC) 66 wt.% dioctyl sebacate (DOS) and 1 wt.% valinomycin applied to an ion-sensitive electrode (ISE) were investigated. The membrane generated a sensitivity value of -9.864E-08 Ω/log10(CK). Though this data set was affected by both the maximum resolution of the I-V curve tracing device and the thin-membrane effect. Selectivity tests following the IUPAC two-solution method in the presence of Na+ as the interfering ion, provided selectivity values of 0.228 and 0.443 with higher ratios of primary ion to interfering ion resulting in higher selectivity coefficients. Additionally, utilizing an illumination test, dielectric constants of 17.71 and 10.88 were calculated dependent on the amount of solvent used during formulation. Fabrication of the FET device also resulted in developments in metal contact materials, nitride film processing, and physical vapor deposition (PVD) processes. With further improvements, it is possible to fabricate a biocompatible, wearable K+-selective monitor for continuously testing dialysis patients.