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.

The compounds 12-phenoxy-dodecane-1-thiol, 4-dodecyloxymercaptophenol and 3-dodecyloxymercaptophenol have been synthesized using a novel synthesis to investigate the effect that the orientation of the functional group has on surface acidity. 3-dodeycloxymercaptophenol and 4-dodecyloxymercaptophenol differ in that the hydroxyl group is substituted on different carbons of the benzene ring. The difference in substitution patterns should present the hydroxyl group in different orientations in the interface between a self-assembled monolayer of the compound and aqueous solutions buffered over a pH range of 3-13. By preparing self-assembled monolayers of these molecules on gold substrates, the ability of the hydroxyl group to donate its proton was shown to depend on the hydroxyl group substitution pattern on the benzene ring through contact angle titration experiments. 3-dodecyloxymercaptophenol clearly showed plateaus at low and high pH with a broad transition between the two plateaus. 4-dodecyloxymercaptophenol showed a clear plateau at low pH but not at high pH, although a transition was observed. Using infrared spectroscopy, it was further shown that the long molecular axis of the benzene ring in 3-dodecyloxymercaptophenol was tilted from the surface normal by 55°. The short molecular axis of the ring was twisted out of the plane of the surface by 28° for self-assembled monolayers of this molecule on gold substrates. In contrast, the tilt angle of 4-dodecyloxymercatophenol was measured to be 46° and was twisted out of the surface plane by 36°. It was also found from cyclic voltammetry experiments in 0.5 M KOH, that the ionized monolayers of 4-dodecyloxymercaptophenol were 2.3 kJ/mol less stable than monolayers of 3-dodecyloxymercaptophenols. This finding suggests that hydrogen bonding and other intermolecular interactions in 4-dodecyloxymercaptophenol are greater than in 3-dodecyloxymercaptophenol. / Ph. D.

Polymers containing less than 10 mol % of ions (ionomers) have been studied in depth for their potential in producing polymers with tailored properties for specific applications. A small molar percentage of ions can be incorporated into a polymer to drastically enhance the properties of the polymer. An ionomer that has been studied is that of isoprene copolymerized with sodium styrene sulfonate (poly(I-co-NaSS)). Research has been performed relating to the synthesis and chemical characterization of the copolymers. However, an in depth study of the way the physical properties are affected by a change in ion concentration has not been presented. Thus, it is the goal of this thesis to synthesize a series of poly(I-co-NaSS) copolymers with varying levels of sulfonated styrene and characterize their physical properties. The poly(I-co-NaSS) polymers, containing a range of 1.15 to 4.74 mol % NaSS, were polymerized using free radical emulsion polymerization. The copolymer compositions were confirmed using combustion sulfur analysis. Dynamic light scattering indicated that large aggregates were present in solution. These aggregates were large enough that capillary intrinsic viscosities could not be measured. Small angle x-ray scattering (SAXS) and thermal analysis showed little change as the ion concentration was increased, while tensile, stress relaxation and adhesion properties were improved. The absence of changes in the SAXS patterns indicated that there was an absence of a well-defined ionic aggregate, while the mechanical properties showed evidence of electrostatic interactions. This can be at least partially attributed to ionic interactions on a smaller scale (doublets, triplets). / Master of Science / This research pertains to the creation of a series of polymers containing small amounts of ionic groups that allow tailoring the properties of the materials. The main component of the polymer is polyisoprene, which is also referred to as “natural rubber”. This material is elastic and can be used as a rubber (gloves) or can be manipulated to create a strong adhesive through addition of ionic groups. The polymers were synthesized with varying levels of ionic groups, creating a series of six polymers. These polymers were tested for their chemical composition (the chemical make-up of the polymers), morphological properties (their phase structure and self-assembly of the polymers on a nanometer to micron scale), and their mechanical properties (the strength, elasticity, and adhesive properties of the polymer). It was determined that in terms of the morphology, the polymer remained mostly unchanged as the ion content was increased, but the mechanical properties improved dramatically. As the concentration of ionic groups increased, the strength of the polymer as well as the adhesive properties of the polymer, also increased. Understanding the structure-property relationships of these copolymers can allow researchers to tailor their structures to fit a desired application.

Carbon quantum dots (CQDs) are the latest generation of carbon nanomaterials in applications where fullerenes, carbon nanotubes, and graphene are abundantly used. With several attractive properties such as tunable optical property, edge-functionalization, and defect-rich chemical structure, CQDs have the potential to revolutionize optoelectronics, electro- and photocatalysis, and biomedical applications. Chemical modifications through the addition of heteroatoms, chemical reduction, and surface passivation are found to alter the band gap, spectral position, and emission pathways of CQDs. Despite extensive studies, fundamental understanding of structure-property relationship remains unclear due to the inhomogeneity in chemical structure and a complex emission mechanism for CQDs. This dissertation outlines a series of works that investigate the structure-property relationship of CQDs and its impact in a variety of applications. First, this relationship was explored by modifying specific chemical functionalities of CQDs and relating them to differences observed in optical, catalytic, and pharmacological performance. While a number of scientific articles reported that top-down or bottom-up synthesized CQDs yielded similar properties, the results herein present dissimilar chemical structures as well as photoluminescent and metal sensing properties. Second, the role of nitrogen heteroatoms in top-down synthesized CQD was studied. The effect of nitrogen atoms on spectral position and fluorescence quantum yield was considerably studied in past reports; however, thorough investigation to differentiate various nitrogen related chemical states was rarely reported. By finely tuning both the quantity of nitrogen doping and the distribution of nitrogen-related chemical states, we found that primary amine and pyridine induce a red-shift in emission while pyrrolic and graphitic nitrogen produced a blue-shift in emission. The investigation of nitrogen chemical states was extended to bottom-up synthesized CQDs with similar results. Finally, top-down, bottom-up, nitrogen-doped and chemically reduced CQDs were separately tested for their ability to act as photodynamic anti-cancer agents. This series of experiments uncovered the distribution of reactive oxygen species produced during light exposure which elucidated the photodynamic mechanisms of cancer cytotoxicity. The results presented in this dissertation provide key insight into engineering finely-tailored CQDs as the ideal nanomaterial for a broad range of applications.

Neutral radicals represent versatile building blocks for the design of new conductive and magnetic molecular materials. In order to obtain good electron transport, materials displaying a high bandwidth W and a low on-site Coulomb repulsion energy U must be generated, and to this end, the pyridine-bridged bisdithiazolyl radicals were developed. As a result of resonance stabilization, these materials possessed a low U, a high thermal stability, and did not dimerize in the solid state. Unfortunately, their crystal structures consisted of slipped π-stack arrays that limited overall bandwidth and afforded Mott insulating ground states. To improve on these systems, two strategies were employed to increase orbital overlap between radicals. The first approach involved the removal of one of the R groups to allow for more superimposed π-stacking in the solid state. Although the desired packing motif was achieved for one derivative, and higher conductivity was observed, a subtle distortion along the π-stacks at low temperature resulted in diamagnetic behaviour, demonstrating the need for steric protection in preventing spin-quenching association in these compounds. The second strategy to improve W was to incorporate the heavier, more spatially diffuse selenium atom into the framework. Three selenium-containing isomers were developed and it was found that conductivity increased with selenium content, with room temperature values reaching 0.001 S/cm. For some derivatives σ-dimerization through the selenium atom is observed, and these compounds exhibited a dramatic response to applied pressure, with conductivity values increasing by 5 orders of magnitude under 5 GPa of pressure. When dimerization is avoided, isomorphous mapping of sulfur for selenium is generally achieved, although for one series of radicals, two space groups were obtained. For this family of compounds the effects of the crystal structure on the transport properties were examined. A series of EHT bandwidth calculations and DFT magnetic exchange energy calculations on a model 1D π-stack of radicals revealed that the experimental properties (both conductivity and magnetism) correlate well to theory, suggesting that the behaviour of these compounds can be predicted based on crystal structure, and that the design of compounds with specific properties may soon be possible.

Neutral radicals represent versatile building blocks for the design of new conductive and magnetic molecular materials. In order to obtain good electron transport, materials displaying a high bandwidth W and a low on-site Coulomb repulsion energy U must be generated, and to this end, the pyridine-bridged bisdithiazolyl radicals were developed. As a result of resonance stabilization, these materials possessed a low U, a high thermal stability, and did not dimerize in the solid state. Unfortunately, their crystal structures consisted of slipped π-stack arrays that limited overall bandwidth and afforded Mott insulating ground states. To improve on these systems, two strategies were employed to increase orbital overlap between radicals. The first approach involved the removal of one of the R groups to allow for more superimposed π-stacking in the solid state. Although the desired packing motif was achieved for one derivative, and higher conductivity was observed, a subtle distortion along the π-stacks at low temperature resulted in diamagnetic behaviour, demonstrating the need for steric protection in preventing spin-quenching association in these compounds. The second strategy to improve W was to incorporate the heavier, more spatially diffuse selenium atom into the framework. Three selenium-containing isomers were developed and it was found that conductivity increased with selenium content, with room temperature values reaching 0.001 S/cm. For some derivatives σ-dimerization through the selenium atom is observed, and these compounds exhibited a dramatic response to applied pressure, with conductivity values increasing by 5 orders of magnitude under 5 GPa of pressure. When dimerization is avoided, isomorphous mapping of sulfur for selenium is generally achieved, although for one series of radicals, two space groups were obtained. For this family of compounds the effects of the crystal structure on the transport properties were examined. A series of EHT bandwidth calculations and DFT magnetic exchange energy calculations on a model 1D π-stack of radicals revealed that the experimental properties (both conductivity and magnetism) correlate well to theory, suggesting that the behaviour of these compounds can be predicted based on crystal structure, and that the design of compounds with specific properties may soon be possible.

For centuries, researchers have been trying to achieve precise control and tailor materials properties. Several approaches, i.e., thermo-activation, electro-activation, and photo-activation, have been widely utilized. As an alternate and fundamentally different approach, mechano-activation is still relatively less-known. In particular, understanding the roles of mechano-activated electronic and molecular structures is yet to be achieved. This research contributes the fundamental understanding in mechanisms of mechano-activation and its effects on materials properties. Experimental investigation and theoretical analysis were involved in the present research. A methodology was developed to introduce the mechnao-activation and to study its subsequent effects. There are three major areas of investigation involved. First, the means to introduce mechanoactivation, such as energetic particle collision or a bending deformation (tensile force); Second, in-situ and ex-situ characterization using AFM, FTIR, UV-Vis, and XPS etc. techniques; Third, theoretical analysis through modified Lennard-Jones potentials in order to explain the behavior of materials under mechano-activation. In the present research, experiments on a Diamond-Like Carbon (DLC) film, a Polyvinylidene Fluoride (PVDF) film, and the Silver-Crown Ether nanochains (Ag-NCs) were carried out. For DLC, the collision-induced transformation between hybridization states of carbon was confirmed, which also dominated the friction behavior of the film. For PVDF, results show that the applied tensile force induced the transformation of [alpha], [beta], and [upsilon] crystalline phase. In addition, the transformation observed was time and direction dependent. For Ag-NCs, a new approach based on the mechanism of mechano-activation was developed for nanochain structure synthesis. Molecular dynamics simulation and experimental results revealed that the formation of Ag-NCs is a synergetic physicalchemical procedure. Experimental results from DLC and PVDF were further used to validate the proposed potential, which brought new insight into the activation process. The current research achieves a precise control on engineering materials properties. The force-activated materials have wide applications in many areas, such as functional coating, sensing, and catalysis. In this study selected experiments have demonstrated the effects of mechanoactivation in different material systems (ceramic, polymer, metallic nano structure) and at different length scales. For the first time, a modified potential was proposed to explain the observed mechano-activation phenomena from the energy point of view. It was validated by experimental results of DLC and PVDF. The current research brings new understanding in mechano-activation and opens potential for its applications in tailoring materials properties.

The present study employs a standardized progressive load scratch test (ASTM D7027/ISO 19252) to investigate the fundamental physical and mechanistic origins of scratch deformation in styrene-acrylonitrile (SAN) random copolymers. Previous findings from numerical simulation using finite element methods are used to establish correlation between mechanical properties and key scratch deformation mechanisms of the SAN model systems. For SAN, the acrylonitrile (AN) content and molecular weight (MW) can be changed to alter mechanical properties such as tensile strength and ductility. The key scratch deformation mechanisms are identified as: scratch groove formation, scratch visibility, periodic micro-cracking and plowing. Groove formation has been correlated to the secant modulus at the compressive yield point while micro-cracking and plowing are related to the tensile strength of the material. The fundamentals and physical origins of scratch visibility are discussed. It is explained how unbiased evaluation is accomplished by means of an automatic digital image analysis software package (ASV®). Frictional behavior and the effects of scratch speed and moisture absorption are also addressed. Increasing the AN content and/or the MW of the SAN random copolymers generally enhances the scratch resistance of the material with regard to the onset of the key deformation mechanisms. Increasing the scratch speed increases the brittleness of the material, resulting in failure at lower applied loads. Moisture absorption increases with AN content and imparts a degree of plasticization as the moisture diffuses into the sub-surface. This plasticization initially results in a degradation of scratch resistance with respect to the key deformation mechanisms, but then, after saturation, the moisture on the surface provides lubrication and improves the scratch resistance. It is important to note that polymers are fundamentally different in nature, but the findings of this study serve as an important stepping stone down the path to a deeper understanding of polymer scratch behavior.

Surrogate fuels are mixtures of pure hydrocarbons that mimic specific properties of a real fuel. The use of a small number of pure compounds in their formulation ensures that chemical composition is well controlled, helping increase reproducibility of experiments and reduce the computational cost associated with numerical modeling. In this work, surrogate mixtures were developed for Jet A fuel based on correlations between fuel properties (cetane number, smoke point, threshold sooting index (TSI), density, viscosity, boiling point and freezing point) and the nuclear magnetic resonance (NMR) spectra of the fuel as a measure of the fuel's chemical composition. Comparison of the chemical composition and target fuel properties of the surrogate fuels developed in this work to a Jet A fuel sample and other surrogate fuels proposed in the literature revealed the superiority of these surrogate fuels in mimicking the fuel properties of interest.

Surrogate fuels are mixtures of pure hydrocarbons that mimic specific properties of a real fuel. The use of a small number of pure compounds in their formulation ensures that chemical composition is well controlled, helping increase reproducibility of experiments and reduce the computational cost associated with numerical modeling. In this work, surrogate mixtures were developed for Jet A fuel based on correlations between fuel properties (cetane number, smoke point, threshold sooting index (TSI), density, viscosity, boiling point and freezing point) and the nuclear magnetic resonance (NMR) spectra of the fuel as a measure of the fuel's chemical composition. Comparison of the chemical composition and target fuel properties of the surrogate fuels developed in this work to a Jet A fuel sample and other surrogate fuels proposed in the literature revealed the superiority of these surrogate fuels in mimicking the fuel properties of interest.