Small angle X-ray scattering (SAXS) has been widely used in polymer science to study the nano-scale morphology of various polymers. The data obtained from SAXS give information about sizes and shapes of macromolecules, characteristic distances of partially ordered materials, pore sizes, and so on. The understanding of these structural parameters is crucial in polymer science in that it will help to explain the origin of various properties of polymers, and guide design of future polymers with desired properties. We have been able to further develop the contrast variation method in SAXS to study the morphology of Nafion 117CS containing different alkali metal ions in solid state. Contrast variation allows one to manipulate scattering data to obtain desired morphological information. At room temperature, only the crystalline peak was found for Na⁺-form Nafion, while for Cs⁺-form Nafion only the ionic peak was observed. The utilization of one dimensional correlation function on different counterion forms of Nafion further demonstrates the necessity of contrast variation method in obtaining more detailed morphological information of Nafion. This separation of the ionic peak and the crystalline peak in Nafion provides a means to independently study the crystalline and ionic components without each other's effect, which could be further applied to other ionomer systems. We also designed time resolved SAXS experiments to study the morphological development during solution processing Nafion. As solvent was removed from Nafion dispersion through evaporation, solid-state morphological development occurred through a variety of processes including phase-inversion, aggregation of interacting species (e.g., ionic functionalities), and crystallization of backbone segments. To probe the real-time morphological development during membrane processing that accurately simulates industrial protocols, a unique sample cell has been constructed that allows for through-film synchrotron SAXS data acquisition during solvent evaporation and film formation. For the first time, this novel experiment allows for a complete analysis of structural evolution from solution/dispersion to solid-state film formation, and we were able to show that the crystallites within Nafion develop later than the formation of ionic domains, and they do not reside in the cylindrical particles, but are dispersed in solution/dispersion. Besides bulk morphology of Nafion, we have also performed Grazing Incident SAXS to study the surface morphology of Nafion. We were able to manipulate the surface morphology of Nafion via neutralizing H⁺-form Nafion with different large organic counterions, as well as annealing Nafion thin films under different temperatures. This not only allows to obtain more detailed information of the nano-structures in Nafion thin films, but also provides a means to achieve desired morphology for better fuel cell applications. We have also been able to study the polymer chain conformation in solution via measuring persistence length by utilizing solution SAXS. Different methods have been applied to study the SAXS profiles, and the measured persistence lengths for stilbene and styrenic alternating copolymers range from 2 to 6 nm, which characterizes these copolymers into a class of semi-rigid polymers. This study allows to elucidate the steric crowding effect on the chain stiffness of these polymers, which provides fundamental understanding of polymer chain behaviors in solution. Self-assembling in block copolymers has also been studied using SAXS. We established a morphological model for a multiblock copolymer used as a fuel cell material from General Motors®, and this morphological model could be used to explain the origins of the mechanical and transport properties of this material. Furthermore, several other block copolymers have been studied using SAXS, which showed interesting phase separated morphologies. These morphological data have been successfully applied to explain the origins of various properties of these block copolymers, which provide fundamental knowledge of structure-property relationship in block copolymers. / Ph. D.

Background There is a transition towards minimally invasive restorative techniques in restorative dentistry based upon reducing bacterial viability and encouraging remineralization of caries infected tissue. To improve the predictability of the antibacterial and remineralization potential of carious dentine by either the application of medicaments or placement of restorative materials that encourage remineralization would be a significant benefit in disease management. Materials and Methods An experimental model was developed using a chemostat for in vitro analysis of the effects of silver fluoride followed by potassium iodide (AgF/KI) and ozone treatment on non demineralized and demineralized dentine. Electron Probe Micro Analysis (EPMA) and Scanning Electron Microscopy (SEM) on the treated dentine were conducted to investigate ion transfer, and biofilm formation. Bacteria growth was measured by optical density. An in vitro caries model using a chemostat was developed to determine the ability of glass ionomer cement and composite resin to inhibit dentinal degradation in adjacent dentine and to measure ion exchange at the restorative interface. Tests were made to determine the bond strength between dentine and glass ionomer cement after application of silver fluoride to the surface of the dentine. Results S. mutans migrated through all dentine samples. Samples treated with AgF/KI had significantly lower optical densities than the corresponding controls. Optical density readings were significantly lower in demineralized dentine treated with AgF/KI than non demineralized dentine. There were lower but not significant differences in the optical density readings between ozonated and non ozonated dentine. An S. mutans biofilm covered all control discs. No biofilm was detected on discs treated with AgF/KI and these discs were significantly more resistant to further demineralization than the control discs. Detectable amounts of silver and fluoride were found up to 450 μm in the AgF and AgF/KI sections. Ozone infusion prevented S. Mutans and L. acidophilus biofilm formation on all the treated dentine samples, biofilm was present on all control specimens. There was calcium and phosphorus present in all auto cure glass ionomer cements to a depth beyond 50 microns. Aluminium and strontium ions were also present in dentine except strontium subjacent to Ketac Molar restorations. Fluoride uptake was significantly higher under glass ionomer cement restorations where the dentine was pretreated with AgF/KI compared to non treated specimens. Silver and iodine deposits were present in demineralized dentine treated with AgF/KI. Calcium and phosphorus levels up to 130 microns from the restorative interface were similar to non demineralized dentine adjacent to auto cure glass ionomer cements and half that adjacent to composite resin. There was significant surface degradation in auto cure glass ionomer cements compared to composite resin. Washing away the AgF/KI precipitate produced higher bond strengths to dentine than samples where the precipitate remained. Conclusions Under the conditions of these in vitro studies, the application of AgF/KI and ozone pharmacologically reduces the initiation and rate of dentine caries. Glass ionomer cements were shown to protect dentine from experimental carious degradation and assist with remineralization. AgF/KI application enhances remineralization beneath glass ionomers and does not interfere with bond strengths. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1344616 / Thesis (Ph.D.) - University of Adelaide, Dental School, 2008

The production of components in polymer electrolyte membrane fuel cells is a widely researched topic and still has a lot of potential for optimization. Especially the reduction of used materials like ionomer and platinum in fuel cell electrodes and the improvement of their performance are highly desired. In this study we discuss the potential of structured cathode catalyst layers by introducing a through plane ionomer gradient. For this purpose different catalyst layers with a platinum loading of 0.25 mg/cm2 have been produced by screen printing, followed by extensive In-Situ characterization in a fuel cell test bench. The results show that combining high amounts of ionomer at the membrane/electrode interface, and decreasing amounts towards the gas diffusion layer enable a good protonic connection of the catalyst layer to the membrane while improving the performance in the high current area due to lower diffusion resistance. This trend was also supported by limiting current measurements, showing increasing diffusion resistances with higher ionomer contents at the gas diffusion layer interface.

Magister Chirurgiae Dentium (MChD) / Background: This study aimed to determine the association between dimensional change and surface roughness (Ra) of Vitremer, Activa and Cention N after immersing them into two different media: acidic and artificial saliva media for the period of a year. Measurements were made at 10 time intervals during the observation period. Methodology: This was a quantitative and qualitative study. For the quantitative part, a total of 60 specimens were tested, 20 specimens for each material. The 20 specimens were further divided into 10 specimens. Ten were immersed in acidic media and the rest in saliva media. A measurement of the weight, height, and Ra was carried out as follows: day 0, day 1, day 2, day 7, day 21, day 28, day 60, day 90, day 180 and day 365. Scanning electron microscopy (SEM) was used to examine the surface of each material qualitatively pre and post immersion in the two media. For fluoride measurements, an additional five samples from each material were left suspended in the de-ionized water by the use of dental floss. The materials were moved to new specimen jars after the completion of day 1, 2, 3, 4, 5, 6, 7, 14, 21 and 28. All the specimen jars had been kept for the fluoride measurements. Results: Non-parametric tests were used to analyze the data. Linear regression analysis was used to measure the association between weight, height or surface roughness (Ra) and immersion time for a year. The result of this test showed that Vitremer had a significant association between the weight (p = 0.000), height (p = 0.007) and Ra (p = 0.001) when it was immersed in acidic media. On the other hand, when Vitremer was immersed in saliva media, only the weight variable showed a significant association (p = 0.002). For Cention N, significant association was found for only Ra when immersed in acidic media (p = 0.000). Finally, for Activa, all the studied associations; the weight, height and Ra in both media were found to be insignificant. For saliva media, there was a significant weight change between the three materials during all 10 periods of time (p = 0.000). In the first six months, Cention N demonstrated a significant increase in weight changes followed by Vitremer, then Activa. Yet, after a year, the difference between Cention N and Vitremer became insignificant and Activa showed the least weight changes. There was not a significant difference between the materials in terms of height and Ra measurements. The fluoride experiment was not successful due to technical issues during pH measurements of the collected solutions. For comparison of the studied parameters between the three materials, the Kruskal-Wallis test was used. In acidic media, there was a significant difference between the materials in term of weight change in 10 periods of time (p = 0.000). In particular, after a two month period, Cention N had the highest weight, followed by Vitremer and then by Activa. The difference between Vitremer and Activa became insignificant throughout the rest of the experimental time frame. All the height measurements between the three materials were found to be insignificant except for day 365 (p = 0.048), where both Activa and Cention N were found to be significantly higher than Vitremer. For the Ra comparison, in the first two weeks, particularly day 1, 7 and 14, Cention N had significantly the lowest Ra among the other materials. As the three materials aged in the acidic media (day 180), Vitremer had significantly the highest Ra values. Cention N showed higher Ra values than Activa; nonetheless this difference was not significant. The SEM images showed loss of some particles in all post-experimental images of the materials in acidic media. Vitremer showed the widest cracks with the loss of fillers. In saliva media, there was also loss of particles but to a lesser extent than in acidic media. Yet, the post-experimental image of Activa in saliva resembled the pre-experimental one. Conclusion: Within the limitations of the study, the best material to resist Ra from prolonged acidic attack was Activa followed by Cention N and then Vitremer. Except for Vitremer, no significant changes in the Ra of the other materials were detected when the three materials were immersed in saliva media in the long term. In acidic media Vitremer tended to lose weight and height faster than Cention N and Activa over a year. Cention N is the best material to resist dimensional change. However, in artificial saliva Vitremer gained water rapidly. Activa did not absorb a lot of water and did not reject a lot of water; Activa demonstrated good dimensional stability and this property may be beneficial when compared to the other two materials tested. The clinical significance of the study: All the materials studied were subjected to dimensional and Ra changes following long-term exposure to acidic substances, but the newer materials (Cention N and Activa) seemed to be more dimensionally stable and resistant to Ra changes than the older, well-known material (Vitremer). This may influence a clinician’s choice of restorative material for use in pediatric dentistry.

Indiana University-Purdue University Indianapolis (IUPUI) / While most sealants available are resin-based, glass ionomer-based cements can be used as sealants, with the advantage of being more tolerant to moisture during placement and of releasing fluoride. The objective of this study was to evaluate the influence of different fissure conditioning techniques on penetration and microleakage of glass ionomer (GI) and resin-modified glass ionomer cements (RMGI) used as sealants. Clinically sound extracted human molars were distributed into nine experimental groups (n = 15 each). Group 1 (control) was sealed with resin-based sealant (Delton) following clinically accepted techniques. Groups 2 through 6 were sealed with RMGI (Vitremer) after having the fissure conditioned with either polyacrylic acid (RMGI-control), 35-percent H3PO4, low viscosity 35-percent H3PO4 with a surfactant, self-etch conditioner, or 35-percent H3PO4 followed by self-etch conditioner. Groups 7 through 9 were sealed with GI sealant (Fuji Triage) after having the fissures conditioned with either polyacrylic acid (GI-control), 35- percent H3PO4 or low viscosity 35-percent H3PO4 with a surfactant. After aging through thermocycling (2500 cycles), specimens were incubated in methylene blue for four hours and sectioned at multiple locations. Digital images were obtained using a digital stereomicroscope, and microleakage was determined by scoring the dye penetration along the enamel-sealant interface. The penetration of the material was determined by calculating the percentage of the total length of the fissure penetrated by the material. Results: The use of self etch-conditioner significantly increased RMGI penetration, while surface conditioning with 35-percent phosphoric acid with surfactant significantly decreased microleakage of GI. The resin-based sealant placed after 35-percent phosphoric acid surface conditioning showed the best penetration and the least level of microleakage. In conclusion, results from this study suggest that the placement of glass ionomer-based sealants can be enhanced by modifying current conditioning methods.

Indiana University-Purdue University Indianapolis (IUPUI) / Background: Since the introduction of glass ionomer cements (GICs) in the 1970s, many attempts have been made to improve them and expand their application in restorative dentistry. Recently, GC America introduced a new glass ionomer restorative system called EQUIA. The manufacturer claims that this material has improved wear resistance by coating the surface of high-strength GIC with a nano-filled resin coating. Objective: The objective of this study was to measure the wear resistance and hardness of EQUIA and to compare it to other current restorative materials. Materials and Methods: Four different materials were used in this study: EQUIA, Fuji IX GP Extra, Fuji II LC and Z-100. Six specimens of each material were made and then tested in a toothbrush abrasion machine for 20,400 cycles, after which the amount of volume loss was calculated. Eight specimens of each material were made and tested in a three-body Alabama wear testing machine under a load of 75 N for 400,000 cycles. Four surface profiles were obtained from each specimen and volume loss was calculated using computer software. Five specimens of each material were made and Knoop microhardness was determined by using the mean of the three values from the top surface of the specimen. Results of each test were collected and compared with the other materials using one-way analysis of variance (ANOVA) at a significance level of 0.05. Results: Wear-resistance results showed that EQUIA has wear-resistance values comparable to composite resin and higher values than those for the high-strength GIC. The results also showed that Fuji II LC had the highest wear among all tested materials. Microhardness results showed that EQUIA has significantly lower microhardness than Fuji IX GP Extra and Z-100. Conclusion: Based on the results of the present study, it can be concluded that coating the surface of glass ionomer restorations with a nano-filled resin coat results in increasing the wear resistance and decreasing the microhardness of the material. Within the limitations of this study, EQUIA has comparable wear resistance to composite resin.

Over the past three decades, the steady decrease in fossil energy resources, combined with a sustained increase in the demand for clean energy, has led the scientific community to develop new ways to produce energy. As is well known, one of the main challenges to overcome with fossil fuel-based energy sources is the reduction or even elimination of pollutant gases in the atmosphere. Although some advances have helped to slow the emission of greenhouse gases into the atmosphere (e.g., electric cars and more fuel-efficient gas-burning automobiles), most experts agree that it is not enough. Proton Exchange Membrane (PEM) fuel cells have been widely recognized as a potentially viable alternative for portable and stationary power generation, as well as for transportation. However, the widespread commercialization Proton Exchange Membrane Fuel Cells (PEMFCs) involves a thorough understanding of complex scientific and technological issues. This study investigated the various structure-property relationships and materials durability parameters associated with PEMFC development. First, the correlation between perfluorinated ionomer membranes and processing/performance issues in fuel cell systems was investigated. As confirmed by small-angle X-ray scattering data, impedance analysis, and dynamic mechanical analysis, solution processing with mixed organic-inorganic counterions was found to be effective in producing highly arranged perfluorinated sulfonic acid ionomer (PFSI) membranes with more favorable organization of the ionic domain. Moreover, thermal annealing was shown to enhance the proton mobility, thereby facilitating reorganization of the polymer backbone and the hydrophilic region for improved crystallinity and proton transport properties. This research also confirmed an increase in water uptake in the solution-processed membranes under investigation, which correlated to an increase in proton conductivity. Thus, annealing and solution-processing techniques were shown to be viable ways for controlling morphology and modulating the properties/performance of PFSI membranes. Second, this study investigated the role of the morphology on water and proton transport in perfluorinated ionomers. When annealed at high temperatures, a significant decrease in water uptake and an increase in crystallinity were observed, both of which are detrimental to fuel cell performance. Additionally, controlling the drying process was found to be crucial for optimizing the properties and performance of these membranes, since drying at temperatures close or above the α-relaxation temperature causes a major reorganization within the ionic domains. Third, although many investigations have looked at key PEMFC components, (e.g., the membrane, the catalyst, and the bipolar plates), there have been few studies of more "minor" components—namely, the performance and durability of seals, sealants, and adhesives, which are also exposed to harsh environmental conditions. When seals degrade or fail, reactant gases leak or are mixed, it can degrade the membrane electrode assembly (MEA), leading to a performance decrease in fuel cell stack performance. This portion of the research used degradation studies of certain proprietary elastomeric materials used as seals to investigate their overall stability and performance in fuel cell environments with applied mechanical stresses. Additionally, characterization of the mechanical and viscoelastic properties of these materials was conducted in order to predict the durability based on accelerated aging simulations as well. Continuous stress relaxation (CSR) characterization was performed on molded seals over a wide range of aging conditions using a customized CSR fixture. The effects of temperature, stress, and environmental conditions are reported in terms of changes in momentary and stress relaxations, chain scission and secondary crosslink formation. Aging studies provided insights on how anti-degradants or additives affect the performance and properties of sealing materials, as well as how a variety of environmental considerations might be improved to extend the lifetime of these elastomers. / Ph. D.

Providing sustainable supplies of water and energy is a critical global challenge. Polymer membranes dominate desalination and could be crucial to power generation applications, which include reverse osmosis (RO), nanofiltration (NF), forward osmosis (FO), pressure-retarded osmosis (PRO), electrodialysis (ED), membrane capacitive deionization (CDI), and reverse electrodialysis (RED). Improved membranes with tailored water and salt transport properties are required to extend and optimize these technologies. Water and salt transport structure/property relationships provide the fundamental framework for optimizing polymer materials for membrane applications. The water and salt transport and free volume properties of a series of sulfonated styrenic pentablock copolymers were characterized. The polymers' water uptake and water permeability increase with degree of sulfonation, and the block molecular weights could be used to tune water uptake, permeability, and selectivity properties. The presence of fixed charge groups, i.e., sulfonate groups, on the polymer backbone influence the material's salt transport properties. Specifically, the salt permeability increases strongly with increasing salt concentration, and this increase is a result of increases in both salt sorption and diffusivity with salt concentration. The data for the sulfonated polymers, including a sulfonated polysulfone random copolymer, are compared to those for an uncharged polymer to determine the influence of polymer charge on salt transport properties. The sulfonated styrenic pentablock copolymer permeability data are compared to literature data using the water permeability and water/salt selectivity tradeoff relationship. Fundamental transport property comparisons can be made using this relationship. The effect of osmotic de-swelling on the polymers and the transport properties of composite membranes made from sulfonated styrenic pentablock copolymers are also discussed. The sulfonated styrenic pentablock copolymers were exposed to multi-valent ions to determine their effect on the polymer's salt transport properties. Magnesium chloride permeability depends less on upstream salt concentration than sodium chloride permeability, presumably due to stronger association between the sulfonate groups and magnesium compared to sodium ions. Triethylaluminum was used to neutralize the polymer's sulfonic acid functionality and presumably cross-link the polymer. The mechanical, transport, and free volume properties of these aluminum neutralized polymers were studied. / text

Purpose: To compare the in-vitro shear bond strengths of a new paste-paste formulation of resin-modified glass-ionomer cement (Rm-GIC) to an exising powder-liquid formulation. The study will test the hypothesis that the new paste-paste formulation of Rm-GIC (Fuji-Cem ™, GC Corp, Tokyo, Japan) has the same bond strength as an existing popular powder-liquid formulation of Rm-GIC (Rely-X ™ Luting Cement, 3M, St. Paul, MN)Materials and Methods: A total of 33 human molars were sectioned parallel to the occlusal surface to expose mid-coronal dentin and mounted parallel to the bond shearing device on the universal testing machine (Instron). For Group I samples (Rely-X, n=15), the powder and liquid were measured and adjusted to achieve a ratio of 1.6 and mixed for 30 seconds as recommended by the manufacturer. For Group II (Fuji-Cem, n=18), the paste-paste was expressed from the paste-dispenser provided by the manufacturer and mixed for 10 seconds as recommended. After testing, the teeth from group II were bonded on a different site with the same material but mixed for 20 seconds (n=18). To ensure a uniform flow and bond surface area, the mixed cement was syringed into a cylindrical mould (diameter 2.38mm, height 2mm) and allowed to set under constant force. All samples were subjected to fracture by shear loading on a universal testing machine (Instron) at a uniform crosshead speed of .02" per minute and expressed as MPa. Values were analyzed at the pResults: Wilcoxon rank sums test showed significantly higher shear bond strength values for Rely-X compared to Fuji-Cem mixed both at 10 seconds and 20 seconds. Mixing for 20 seconds resulted in stronger bonds for Fuji-Cem compared to 10 seconds, but was still significantly lower than Rely-X.Conclusions: Within the limitations of the study, the Rely-X powder-liquid formula shows a significantly stronger dentin shear bond strength when compared to the new paste-paste formula of resin-modified glass ionomer cement, Fuji-Cem.

Les nanocomposites à matrice polymère et plus particulièrement les élastomères chargés intéressent depuis de nombreuses années la communauté scientifique du fait notamment de leurs bonnes propriétés mécaniques. Il est établi que l'amélioration des propriétés mécaniques observées dans les élastomères renforcés par des charges nanoscopiques est principalement due à des effets de structure (dispersion des charges) et à des effets d'interface (interactions charges/matrice). Afin d'alimenter la discussion sur l'origine du renforcement dans les élastomères chargés, cette étude s'intéresse à la synthèse et à la caractérisation de nanocomposites modèles pour lesquels les interactions charges/matrice et la microstructure sont maîtrisées. En parallèle, ce travail propose également une analogie entre ces systèmes et les ionomères, matériaux constitués de macromolécules sur lesquelles des groupements ioniques sont greffés. Ces matériaux ionomère présentent des propriétés originales et permettent la création de nœuds de réticulation réversibles avec la température / In polymer-based nanocomposites macroscopic properties are driven by one specific feature: the huge interfacial area developed by nanofillers, leading to a strong improvement in mechanical properties. Even though the molecular origins of this reinforcement are still not well understood, its amplitude appears to be strongly related to two main effects: a structural effect (dispersion state) and an interfacial effect (filler/matrix interactions). The present project aims at developing and studying organic-inorganic nanocomposite materials based on an elastomeric matrix and spherical nanoparticles. A specific attention is paid to get tailored interactions and microstructures, different model nanocomposites are obtained with interesting and original thermo-mechanical properties. In parallel, this work also gives an analogy between these nanocomposite and ionomers, polymer chains on which ionic groups are grafted. These ionomer materials show original mechanical properties and allow creating reversible crosslink nodes with temperature