In this research, influence of different levels of Closite Na+ additives on the microstructure, morphology and mechanical properties of polymer products was studied. Importance was given to understand the additive level, extent of dispersion in matrix, change in microstructure and respective property observed in the end product. Polypropylene spunbond and meltblown web samples with various levels of Closite Na+ additives were produced and characterized. Injection molded polypropylene nanocomposite with 1 to 15 wt% nanoclay additives were also prepared and characterized for microstructure and mechanical properties. Crystallization kinetics studies showed significant increase in crystallization rates on nylon 6 even at 0.25 wt % additives. Near surface and bulk stiffness of the film significantly increased in the presence of nanoclay additives. Intercalated and flocculated morphology was observed for all the polypropylene concentrate and the same morphology was retained in spunbond fibers also. About 25 to 30 % increase in cross direction tear strengths were observed for 1 to 2 wt % clay loading. Fibers with even as low as 1 % clay retains their morphology and integrity in bond point after thermal bonding. At higher weight percentage, stiffness of webs significantly increased and tear strength of webs decreased due to exclusion of excess clay platelets in the interspherulite regions. Property benefits were not observed in the case of melt blown samples with nanoclay additives, but the additives were well dispersed in the fiber web. Compared to control meltblown webs, stiff and open web structure with high irregularity was obtained for samples with clay additive. In case of injection-molded polypropylene composite, significant increase in breaking energy was observed for sample with just with 1 wt % clay additive. At higher weight percentage, segregation was observed in the inter-spherulitic region and failure mode shifted from ductile to brittle.

Effects of radiation (gamma and proton) on Ultra High Molecular Weight Polyethylene (UHMWPE) is studied for prosthetic joints and for radiation shielding for manned space missions. The first section of the dissertation will cover gamma radiation effects on UHMWPE by means of solubility, hardness, three-phase model, crystallite thickness, and molecular mobility studies. The second part will cover proton radiation effects on UHMWPE by means of solubility, three-phase crystallite model, and crystallite thickness study. The combined studies of the gamma irradiated samples shows that chain scission occurs on the surface and crosslinking in the center. The combined studies of the proton irradiated samples show that crosslinking occurs in the amorphous region and breaking of the tie chains and loops causes the growth of the already existing crystals. A new method has been developed to analyze DSC data based on crystallite thickness that generates crystallite thicknesses (number-average, weight-average, and z-average) and the lamella thickness polydispersity index, PDI (lw/ln and lz/ln). This new analysis method agrees with all other experiments conducted on the samples (solubility, molecular mobility, and three-phase model analysis).

In some breeds of dog, specifically the Yorkshire Terrier, a genetic defect exists that causes a hepatic portosystemic shunt to form. A hepatic portosystemic shunt is a vessel that when present cause blood to bypass the liver, which is responsible for filtering waste from the digestive system and moving it out of the body. An implantable polymeric device was constructed that would slowly occlude the hepatic portosystemic shunt and force the blood to stop flowing through the bypassing vessel and flow through the vessel to the liver over 3-4 months time. The portosystemic shunt occluder device consist of three polyoxymethylene components, a swelling hydrogel (poly (acrylic acid)), and a degrading copolymer – (Poly (lactide-co-caprolactone)). The poly (acrylic acid) was used to move the piston component of the device upward to constrict the portosystemic shunt placed inside the device. Eight milligrams of poly (acrylic acid) had a swelling ratio of 20.10 ± 1.63, a swelling rate of 0.071 mm/s2, and generated 25mN of force. Eight milli-Newtons is the amount of force that is produced by blood flowing in a four milli-meter diameter vessel. The degradation properties of two compositions of poly (lactide-co-caprolactone) (40 percent lactide and 60 percent caprolactone; 86 percent lactide and 14 percent caprolactone) were analyzed and relationships were developed that would aid in determining the degradation rate of the copolymers in respect to the copolymer composition and the environmental temperature. The poly (lactide-co-caprolactone) controlled the rate that the piston moved by providing a counter force to the poly (acrylic acid). The poly (lactide-co-caprolactone) (40:60), when loaded into the device, degraded in 86 days in a phosphate buffered saline solution at a temperature of 37oC.

Cotton based highloft nonwovens have been used in consumer goods such as pillows, upholstered furniture and mattresses for years. Cotton provides comfort, soft hand and cost effectiveness to these products. In contrast to its desirable properties, cotton products have a higher proneness to burning and are characterized as highly flammable materials. During the last decade, the fire safety has been an important issue, and there has been increasing focus on approaches to reduce hazardous fire risks and effects. Incorporating flame resistant (FR) chemicals and fibers is one of the most effective methods to improve thermal resistance of cotton to ignition, and provide high degree of flame retardancy performance in the final product. The major aim of using flame retardants is to provide more time for people to escape from fire and reduce death and injuries. Most of the approaches to produce FR cotton based nonwovens are for applications where durability is not important. For some of the applications wash durability is desired and needed. The focus of this research was to develop semi-durable and durable FR treatments for cotton rich nonwovens in an economical way using a binder fiber, going through-air bonding process and treating them with commercially available FR chemicals in the presence of a chemical binder. These FR treated webs have been evaluated for their FR performance before and after washing. Selected FR chemicals and binder types have effect on the wash durability of the produced webs. Selection of appropriate chemicals and binders in the right combination is important so that desired degree of flame resistancy can be achieved. A neural network model was used to understand these effects, so it can help in selecting the best combination for optimum FR performance and reveal the unknown behavior of FR characteristics. Also, importance of FR chemical type, chemical binder type, chemical add on level and binder percentage based on flammability results was revealed through a statistical analysis.

Cotton based highloft nonwovens have been used in consumer goods such as pillows, upholstered furniture and mattresses for years. Cotton provides comfort, soft hand and cost effectiveness to these products. In contrast to its desirable properties, cotton products have a higher proneness to burning and are characterized as highly flammable materials. During the last decade, the fire safety has been an important issue, and there has been increasing focus on approaches to reduce hazardous fire risks and effects. Incorporating flame resistant (FR) chemicals and fibers is one of the most effective methods to improve thermal resistance of cotton to ignition, and provide high degree of flame retardancy performance in the final product. The major aim of using flame retardants is to provide more time for people to escape from fire and reduce death and injuries. Most of the approaches to produce FR cotton based nonwovens are for applications where durability is not important. For some of the applications wash durability is desired and needed. The focus of this research was to develop semi-durable and durable FR treatments for cotton rich nonwovens in an economical way using a binder fiber, going through-air bonding process and treating them with commercially available FR chemicals in the presence of a chemical binder. These FR treated webs have been evaluated for their FR performance before and after washing. Selected FR chemicals and binder types have effect on the wash durability of the produced webs. Selection of appropriate chemicals and binders in the right combination is important so that desired degree of flame resistancy can be achieved. A neural network model was used to understand these effects, so it can help in selecting the best combination for optimum FR performance and reveal the unknown behavior of FR characteristics. Also, importance of FR chemical type, chemical binder type, chemical add on level and binder percentage based on flammability results was revealed through a statistical analysis.

In this work we study three systems of biological interest: the translocation of a heterogeneously charged polymer through an infinitely thin pore, the wrapped of a rigid particle by a soft vesicle and the modification of the dynamical properties of a gel due to the presence of rigid inclusions. We study the kinetics of translocation for a heterogeneously charged polyelectrolyte through an infinitely narrow pore using the Fokker-Planck formalism to compute mean first passage times, the probability of successful translocation, and the mean successful translocation time for a diblock copolymer. We find, in contrast to the homopolymer result, that details of the boundary conditions lead to qualitatively different behavior. Under experimentally relevant conditions for a diblock copolymer we find that there is a threshold length of the charged block, beyond which the probability of successful translocation is independent of charge fraction. Additionally, we find that mean successful translocation time exhibits non-monotonic behavior with increasing length of the charged fraction; there is an optimum length of the charged block where the mean successful translocation time is slowest and there can be a substantial range of charge fraction where it is slower than a minimally charged chain. For a fixed total charge on the chain, we find that finer distributions of the charge along the chain leads to a significant reduction in mean translocation time compared to the diblock distribution. Endocytosis is modeled using a simple geometrical model from the literature. We map the process of wrapping a rigid spherical bead onto a one-dimensional stochastic process described by the Fokker-Planck equation to compute uptake rates as a function of membrane properties and system geometry. We find that simple geometrical considerations pick an optimal particle size for uptake and a corresponding maximal uptake rate, which can be controlled by altering the material properties of the membrane. Finally, we use a mean field approximation, neglecting correlations among the embedded particles, to examine the effect of inclusions in a viscoelastic medium on the effective macroscopic properties of the gel. We find an essentially linear dependence of both components of the complex shear modulus up to arbitrary volume fractions of the inclusions, in contradiction to experimental observations. We conclude that the incorporation of correlations among the particles is needed in order to explain experiments, in analogy with the elastic case.

<p>The energy diagram for organic photovoltaics (OPV), involving the bulk heterojunction (BHJ), on which the device analysis is usually based, has long been a subject of debate. The widely used Metal-insulator-Metal model and P-type Schottky Junction model, both of which are based on inappropriate assumptions, could be incorrect to explain the working principle of BHJ OPV.</p> <p>To further explore the controversy, we start the investigation from the opposite direction, to the usually asymmetrical OPV, involving electron and hole passages, by introducing a pair of symmetric electrodes to a BHJ, to form a completely symmetrical device structure, which, in theory, would produce zero output.</p> <p>Surprisingly, it is found that such a symmetrical device exhibits asymmetrical I-V curves. In particular, it produces a non-zero open-circuit voltage, and a finite short-circuit current. The cause of the output was the asymmetrical charge carrier distribution due to the asymmetrical illumination. To explain the operational mechanism of the symmetrical device, the equivalent circuit including a pair of inverse-parallel diodes and a new model for the BHJ energy diagram are introduced. Those findings would certainly improve the understanding of the device physics of OPV, especially the working principle for BHJ.</p> / Master of Materials Science and Engineering (MMatSE)

Polymer membranes are used extensively in large lightweight structures applications such as superpressure balloons. Design of these structures for long-term operations requires accurate modeling and characterization of the permanent deformation appearing in the structures due to the time and temperature-dependent properties of polymers. This work presents analytical, numerical, and experimental investigations of the onset of residual strains of a viscoelastic polymer membrane subjected to creep loading at various temperatures. The aim of this study is to establish a model that can be employed to determine the time-to-yield given the stress and temperature history a polymer membrane experiences. Two possible time-dependent criteria, the free energy criterion and the kinematic criterion are formulated for the material and their performances are investigated with the experimental data. The experimental data consist of uniaxial and biaxial material behavior characterization and residual deformation experiments are carried out at various temperatures. Biaxial experiments are conducted with the novel inflated cone experimental setup. The inflated cone method leverages the specimen geometry to achieve a non-uniform stress field when differential pressure is applied. The resulting non-uniform strain field is captured with full-field displacement measurement methods, i.e., digital image correlation. This method accelerates the experimental data collection process. The free volume nonlinear viscoelastic model for the material is calibrated with the experimental data obtained at various temperatures and stress levels. The developed kinematic model in conjunction with the nonlinear viscoelastic model can be used to estimate the residual strains if the stress and temperature history a polymer membrane experiences are given. Similarly, the criterion can be used in an inverse design problem to limit the creep stresses and corresponding allowable durations.

Lost Foam Casting (LFC) is a metal casting technology that facilitates fabrication of near-net shape metal castings using expanded polystyrene (EPS) foam patterns that are coated with refractory slurry and is effective for producing aluminum or iron castings of complicated geometry. However, the LFC process can produce considerable amount of scrap due to casting defects. Removing the EPS thermal decomposition products through the ceramic coating ahead of the advancing metal front during the liquid metal pour is a key factor in obtaining a defect free casting. Developing a fundamental understanding of foam degradation mechanism is essential in improving LFC process. Modeling of the LFC process till date has completely neglected the effect of styrene on the overall thermal degradation of EPS foam. The dissolution effect of styrene is investigated by presenting the thermodynamic principles of polymer solution theory along with experiments to verify its impact on polystyrene degradation. By subjecting EPS Foam samples directly either to thermal radiation or to styrene vapor, it is demonstrated that styrene’s solubility of polystyrene significantly alters the degradation mechanism of EPS foam in LFC process and thus can control the metal fill process leading to reduction of defects in castings. LFC process uses expanded polystyrene foam patterns in which isomers of pentane are used as blowing agents to achieve the expansion. In order to expand polystyrene, steam is used as a heat source and the expansion process takes place via conduction of heat from the surface of unexpanded polystyrene beads into the bulk. Pentane isomers are volatile organic compounds and green house gases that are either liberated directly into the atmosphere or combusted using expensive setup. The environmental impact of the current process using pentane as an expansion agent has been considered and a new method for manufacturing of EPS foam has been developed with benign expansion agent. Laboratory experiments are demonstrated where PS pellets are successfully expanded into foam. Novel heating technology using microwave radiation is proposed and implemented in order to achieve efficient volumetric heating for the manufacturing of foam with target density.

The objective of this study is to investigate the relationship among process, structure, and property of the UTSI pitch-based carbon fibers and optimize carbon fiber’s mechanical properties through the stabilization process. Various analysis techniques were employed throughout these investigations which include the Scanning Electron Microscope (SEM), optical microscope, Dia-stron system, MTS, and ImageJ. Several fiber process techniques including fiber spinning, stabilization, and carbonization were explored to determine the effect of the thermal process on the fiber yield, fiber diameter, the sheath-core structure of stabilized fibers, the pac-man and hollow core structures of carbonized fibers, and the resulting mechanical properties of the carbon fibers. It was found that stabilization time and the temperature stepping had a great deal on influence on the resulting carbon fibers. Larger diameter fiber is easy to form sheath-core structure in the stabilization process. Pac-man structure was developed at 600°C during the carbonization. Both stabilization duration and the carbonization temperature control the resulting carbon fiber diameter and fiber structure defects such as the pac-man and hollow core defects. Multi-step stabilization can reduce the total stabilization duration and improve the mechanical properties of the resulting carbon fibers. Fiber structure non-uniformities including fiber diameter distributions for a bundle fiber or along a single fiber, and pac-man angles were determined. Statistical analysis revealed the distribution of the carbon fiber cross-sectional areas and the result is compared against commercial available carbon fibers. Carbon fiber sandwiched composites (CFSCs) were fabricated with UTSI carbon fiber and commercial PAN-based carbon fibers. Several configurations of sandwich structured composites were explored to test the flexural properties with varying sandwich thickness.