As a part of a larger effort towards the fundamental understanding of structureproperty relationship in nanoplatelet-reinforced polymer nanocomposites, a set of model epoxy systems containing α-Zirconium Phosphate (α-ZrP) have been prepared and studied in this dissertation. A new surface modification approach, i.e., the porous pathway approach, for improving intercalation efficiency and exfoliation of layered nanoplatelets has been proposed and the effectiveness has been demonstrated. In order to clearly understand the roles of nanofillers and the effects of their geometric factors on the physical and mechanical properties of nanocomposites, variables such as nanoplatelet loading level, degree of exfoliation, and aspect ratio have been carefully controlled in the epoxy matrices. Morphological information of the prepared nanocomposites was unambiguously confirmed by carrying out X-ray diffraction and transmission electron microscopy (TEM). Tensile and thermo-mechanical properties of the model epoxy/α-ZrP nanocomposites have been investigated. Furthermore, fracture behavior of the model nanocomposites is examined in this study. This work has enhanced the understanding of the effects of nanoplatelet, i.e., loading level, degree of exfoliation, aspect ratio, and the type of surface modifiers, on the mechanical properties and fracture behavior of polymer nanocomposites.

No description available.

Integration of material composition, microstructure, and mechanical properties with geometry information enables many product development activities, including design, analysis, and manufacturing. To address such needs, models of material composition have been integrated into CAD systems, creating systems called heterogeneous CAD modeling. In order to support the heterogeneous CAD system, extensive process-structure-property relationships have to be captured and integrated into current CAD system. A new method for reverse engineering of materials will be presented such that microstructure models can be constructed and used in the heterogeneous CAD system. Reverse engineering of material consists of three parts: image analysis, structure-property-process relationship, and repository. In this research, an image processing method, which comprises the Radon transform and the wavelet transform, will be used in order to recognize geometric features from a microstructure image. Recognizing geometric features can be obtained by combinations of three techniques, masking, clustering, and high frequency component on wavelet transform, that are integrated with the Radon transform. Then, recognized geometric features can be used to construct an explicit geometric model of microstructure. The proposed work will provide an explicit mathematical method to recognize and to quantify microstructure features from an image. In addition, explicit geometric models of microstructure can be automatically constructed and utilized to get effective mechanical properties, establishing structure-property relationship of the material. In order to demonstrate this, polymer nano-composite sample and metal alloy sample will be used.

The reformulation of pressurized metered dose inhalers (MDIs) with hydrofluoroalkanes (HFAs) from chlorofluorocarbons (CFCs) has given rise to many solubility challenges. Compounds and excipients previously used in CFCs were observed to have significantly different solubility values in HFA-134a. In this investigation, the solubility values of solid organic solutes were determined in pure HFA-134a and HFA-134a with cosolvent (0 - 20% w/w ethanol). The solubilities of solid solutes in HFA-134a were also compared with those in 2H,3H-decafluoropentane (DFP) in order to assess the suitability of DFP as a liquid model propellant. The experimental set of solutes display diverse physico-chemical properties and yielded solubility values that ranged over four orders of magnitude. The experimental solubilities were compared to calculated values obtained from ideal solubility and regular solution theory models. While the theoretical models did not offer absolute solubility estimations, a clear correlation with the ideal solubility (melting point) was noted. Further consideration utilizing multiple linear regression models afforded correlations based on molecular properties. Regression models, containing melting point and logP (or molar volume) resulted in promising correlations in both pure HFA-134a and HFA-134a/cosolvent systems where the average absolute errors ranged from 0.49 to 0.82 log units, (average factor errors of 3.09 and 6.61, respectively). In general, a linear relationship was observed between log mole fraction solubility in HFA-134a and fraction ethanol. The effect on solubilization ranged from 1.3 to 99.4 times when 20% w/w ethanol was introduced, relative to pure HFA-134a. DFP appears to be a promising liquid model for pure HFA-134a for pre-formulation calculations. A two parameter equation were found to be significant in pure HFA-134a where the average absolute error (AAE) value was 0.61 log units (average factor errors of 4.07).

Incorporation of water molecules in the crystal structure of an organic compound has strong effects on its physical and chemical properties. Therefore, the study on stability of water-incorporated pharmaceutical compounds and mechanisms of hydration and dehydration is very important for the pharmaceutical industries. The main goals of the present research project were quantitative description of the crystallization and solid-state transformations of pseudopolymorphs of sodium naproxen in order to provide fundamental information concerning stability of the pseudopolymorphic forms. Furthermore, macroscopic phenomena of size reduction and anisotropic water-removal by dehydration were rationalized by microscopic aspects of crystal lattice structures. The heats of solution for each pseudopolymorph were estimated by fitting the solubility data with the vant Hoff equation, and their use was extended by the thermodynamic cycle developed in the present study. According to the thermodynamic cycle, for an enantiotropic system, a form with a lower degree of hydration always has the lower heat of solution than a form with a higher degree of hydration, implying that a form with a lower degree of hydration is more stable. The relative stabilities of the dihydrated, the monohydrated, and the anhydrous sodium naproxen at 0% relative humidity were investigated by dehydration of the dihydrated form and powder X-ray diffraction. The monohydrate is more stable than the dihydrate and the result was supported by isothermal TGA experiments. This research explained why powder-like crystals of the anhydrous sodium naproxen were produced by dehydration of hydrated forms. The surfaces of the dehydrated crystals displayed cracks aligned along the b-axis of the monohydrate. These cracks made the anhydrous crystals, which were produced from the monohydrated species, very brittle and, eventually, such crystals were disrupted into much smaller entities. In addition, the existence of water channels in the unit cells of the monohydrate facilitates the dehydration in a direction more rapidly, especially, along the b-axis of the monohydrate. Rapid removal of water in a specific direction caused anisotropic dehydration.

This dissertation work addresses two important aspects of nanotechnology - stable dispersion and self-assembly of colloidal nanostructures. Three distinctly different types of nano-scaled materials have been studied: 0-dimensional ZnO quantum dots (QDs), 1-dimensional carbon nanotubes (CNTs), and 2-dimensional alpha-zirconium phosphate (ZrP) nanoplatelets. Specifically, highly crystalline ZrP layered compounds with differences in diameters have been synthesized and fully exfoliated into monolayer platelets with uniform thickness, followed by their self-assembly into liquid crystalline structures, i.e., nematic and smectic. A novel colloidal approach to debundle and disperse CNTs has been developed by utilizing nanoplatelets to gather and concentrate sonication energy onto nanotube bundles. In such a fashion, CNTs are fully exfoliated into individual tubes through physical means to preserve their exceptional physical properties. Moreover, monodisperse ZnO QDs with high purity have been synthesized through a simple colloidal approach. Exfoliated ZrP nanoplatelets are used to tune the dispersion of ligand-free ZnO QDs from micron-sized aggregates to an individual QD level depending on the ratio between nanoplatelets and QDs. Dynamic analysis suggests that the dispersion mechanism mainly involves the change of QD dispersion free energy due to the presence of nanoplatelets, so that QDs can interact favorably with the surrounding media. In addition, the nanoplatelet-assisted dispersion approach has been utilized to disperse QDs and CNTs into polymeric matrices. Dispersion - property relationship in polymer nanocomposites has been systematically investigated with emphasis on optical properties for QDs and mechanical properties for CNTs.

This study focuses on the evolving microstructure and its associated mechanical properties during each step of a seven step manufacturing process for 1010 steel tubing. For the microstructural analysis, we employed optical microscopy to quantify the ferrite grain size and pearlite grain size at each material step. To determine the mechanical properties, we used a Vickers hardness indenter and performed both tension and compression tests at varying strain rates and temperatures. Mechanical tests results indicate decreasing strength with increasing grain size, agreeing with the Hall-Petch relation and were used to correlate hardness and yield strength with grain size. Additionally, tensile and compression tests were performed at different strain rates to examine the effect of microstructural features on the mechanical properties of the steel tubing. Understanding the structure/property relationships of 1010 steel tubing during different processing conditions allows tubing to be manufactured more efficiently with desirable mechanical properties.

Gels are used in many applications ranging from bioengineering and pharmaceuticals to food technology and soft-robotics because of their tunable physical and mechanical properties. In many of these applications, the materials need to sustain large deformation. The microstructure of gels changes significantly at large strain values, causing a deviation in the stress responses from that at low strain. The desired mechanical responses of gels can be obtained by tuning their microstructure, therefore, the structure-property relationship for gels is required to be understood for their practical applications. This dissertation discusses two types of gels, one consists of chemical crosslinking and hydrophobic associations, and the other gel only consists of physical crosslinking. The microstructure of these two gel systems is investigated and related to their mechanical responses. The gel system with chemical and physical crosslinking mimics properties of biomaterials like resilin. Resilin is a protein-elastomer that enables biological species for power amplified activities by taking benefits of specific responses of hydrophilic and hydrophobic segments. Inspired by the microstructure and mechanical properties of resilin, a stretchable and resilient hydrogel was synthesized through a simple free radical polymerization technique. These gels retract from the stretched state to the original state with high speed over a short time, such behavior has not been frequently reported for synthetic hydrogels. This gel is also capable of performing a power-amplified activity like catapulting an object. In addition to retraction experiments, the mechanical properties of this gel were investigated in tensile and cyclic loading to determine their resilience. The hydrophobic polymer concentration affects the swelling behavior and mechanical responses such as stretchability and resilience. The second gel system considered here is a physically assembled ABA triblock copolymer dissolved in a B-selective solvent. Here, two different triblock copolymers with different concentrations were utilized. The real-time microstructural change was captured using a RheoSAXS setup with a high flux X-ray beam. The real-time microstructure of these gels subjected to temperature, varying oscillatory strain amplitude, and during relaxation after step strain was captured. This dissertation advances the understanding of the structure-property relationship of microstructurally complex gels towards their potential practical applications.

No description available.

Poly(arylene ether)s are a well-established class of thermoplastics that are known for their mechanical toughness, thermal stability, and fabrication into membranes. These materials can undergo a myriad of modifications including backbone structure variability, sulfonation, and crosslinking. In this dissertation, structure-property relationships are considered for poly(arylene ether)s with regard to membrane applications for proton exchange and gas separation membranes. All of the proton exchange membranes in this dissertation focus on a disulfonated poly(arylene ether sulfone) based hydrophilic structure to produce hydrophilic-hydrophobic multiblock copolymers. The hydrophobic segments were based upon poly(arylene ether benzonitrile) polymers and copolymers. The oligomers were synthesized and isolated separately, then reacted under mild conditions to form the alternating multiblock copolymers. Structure-property relationships were considered for two different proton exchange membrane applications. One multiblock copolymer system was for H2/air fuel cells, and the other for direct methanol fuel cells (DMFCs). The H2/air fuel cells operate under harsh conditions and varying levels of relative humidity, while the DMFCs operate in an aqueous environment with a methanol-water mixture (typically 0.5-1 M MeOH). Thus two different approaches were taken for the multiblock copolymers. All of the multiblock copolymers were cast into membranes and after annealing resulted in drastically reduced water uptake as compared to random and non-annealed systems. The membranes were characterized with regard to composition, mechanical properties, morphology, water uptake, proton conductivity, and molecular weight. Membranes were also sent to collaborators to elicit the fuel cell performance of the proton exchange membranes. In H2/air fuel cells the approach was to increase charge density by bisphenol choice in the hydrophilic phase. This was performed by switching to a lower molecular weight monomer, hydroquinone, and a monosulfonated hydroquinone. This produced higher charge density in the hydrophilic phase, and the corresponding multiblock copolymer. With increased hydrophilicity the multiblock copolymers showed increased phase separation, proton conductivity, and better performance under relative humidity testing. In the second system for DMFCs, the primary goal was to reduce methanol permeability by bisphenol selection in the hydrophobic phase. This was done with by replacing fifty mole percent of the fluorinated monomer with a series of increasing hydrophobicity bisphenols. Addition of benzylic methyl groups on the bisphenols, was the method undertaken to increase the hydrophobicity. The combination of reduced fluorine content along with the addition of methyl groups resulted in multiblock copolymers with extremely low water uptake and methanol permeability. This allowed for a PEM with better performance than Nafion® in 1M MeOH in DMFC testing. The gas separation membranes presented in this dissertation are based upon poly(arylene ether ketone)s. Two systems were presented: one with a polymer directly synthesized with a bisphenol containing benzylic methyl groups and 4,4'-difluorobenzophenone, and the other a difunctional poly(phenylene oxide) oligomer polymerized with 4,4'-difluorobenzophenone. These systems were crosslinked via UV light through excitation of the ketone group to the triplet state and then hydrogen abstraction from the benzylic methyl. Confirmation of crosslinking was performed via differential scanning calorimetry and infrared spectroscopy. Changes in the glass transitions between crosslinked and non-crosslinked materials were characterized with respect to the concentration of ketones to elicit the effects of crosslink density on the polymers and copolymers. Gas transport properties showed a strong dependence on the ketone percentage as the selectivity was much higher for the homopolymer, while the permeability was higher for the PPO copolymer in the CO2/CH4 and O2/N2 gas pairs. / Ph. D.