<p>The Eliashberg theory of superconductivity has been very successful in accounting for properties of conventional materials. The price of this success has been a lack of understanding of exactly what features of the input parameters affect the superconducting properties in significant ways. The first part of this thesis is concerned with the identification of an important parameter in the study of thermodynamic, critical magnetic field, and electromagnetic properties of a superconductor. The Bardeen-Cooper-Schreiffer (DCS) theory of superconductivity produces laws of corresponding states, i.e., various properties are predicted to have universal values. We have studied the deviations from the BCS theory due to retardation effects, which are embodied in Eliashberg theory. These deviations, or corrections to BCS, can be well understood and characterized by a single simple parameter, to be defined later. Attention has been focused on reproducing numerical (theoretical) results, since for the most conventional superconducting materials, experiment agrees with theory at the 10% level.</p> <p>The second half of the thesis has been largely motivated by the recent discoveries of the high-Tc oxide materials. We have applied Eliashberg theory almost entirely in the inverse manner. That is, with little knowledge of the microscopic parameters for these new materials, we have investigated the relationships between various macroscopically observable properties, based on model spectra. The model spectra have been of three general types, the conventional category, spectra based on a combined phonon-exciton mechanism, and thirdly those based on relatively low frequency exchange bosons. We have called this latter category the very strong coupling regime. It was hoped that measured properties could uniquely specify the type of spectrum responsible for the superconductivity in the high-Tc oxides. At this point in time this goal has not really been achieved. Too many uncertainties exist in the experimental properties, a situation which has been aggravated by a lack of single crystal data. Moreover, various kinds of measurements on the same property often give very different results. At the same time the theory needs to be improved upon. For example, anistrophy ought to be incorporated into our results, since the single crystals are displaying large anisotropies. Nonetheless, some interesting signatures for the various spectral regimes have been obtained, and these are presented in the latter half of the thesis.</p> / Doctor of Philosophy (PhD)

World energy crisis has triggered more attention to energy saving and energy conversion systems with high efficiency. There is a growing awareness that nanoscience and nanotechnology can have a profound impact on energy generation, conversion, and recovery. Nanotechnology-based solutions are being developed for a wide range of energy problems such as, solar electricity, hydrogen generation and storage, batteries, fuel cells, heat pumps and thermoelectrics. This thesis deals with the design and fabrication of novel functional materials/architectures for energy-related applications. The study includes two parts: Nanostructured thermoelectric (TE) materials for energy conversion and nanostructured metallic surfaces for energy heat transfer. In the first part, the focus is given to the fabrication of novel nanostructured TE materials and architectures. TE materials are very important functional materials that can convert heat to electrical energy and vice versa. Recently, nanostructuring TE materials showed very promising potential to improve their TE figure of merit which opens a new venue for the TE world. As a result, some advanced nanostructured TE architectures are proposed as the state-of-the-art TE materials/structures. Among these advanced TE architectures, bismuth telluride nanowires/thick films and skutterudite nanocomposites with nanoinclusions have been successfully fabricated and some of their advantageous TE performance has been demonstrated. For example, an improvement of 11% on the figure of merit, ZT, was achieved in the CoSb3 nanocomposite with 5 mole% ZrO2 as nanoinclusion. Comprehensive physico-chemical characterization techniques have been used for the synthesized TE materials. The potential-Seebeck microprobe, 4-point probe and laser flash apparatus have been used for the measurement of TE parameters on the TE materials. In the second part of the thesis, we developed a nanostructured macro-porous (NMp) surface for enhancing heat transfer in boiling process. Enhanced surfaces for boiling improve the energy efficiency of heat pumping equipment such as air conditioners, refrigerators, etc. Conventional techniques currently used for fabricating enhanced surfaces are often based on the use of complicated mechanical machine tools and require a large consumption of materials and give only limited enhancement of the boiling heat transfer. In this thesis, we present a new approach to fabricate enhanced surfaces by using electrodeposition under specific conditions forming in-situ dynamic gas bubble templates. As a result, the NMp metallic surface layer comprising of dendritically ordered copper branches is obtained. Since the structure is formed during the evolution of the dynamic bubbles, it is ideal for the bubble generation applications such as boiling. The efficiency of the NMp surfaces for boiling heat transfer was evaluated in pool boiling experiments. At the heat flux of 1 W/cm2, the heat transfer coefficient for the NMp surface is found to be more than 17 times higher than the reference surface. It's estimated that such an effective boiling surface would improve the energy efficiency of many heat pumping machines with 10 - 30 %. The extraordinary enhancement of boiling performance is explained by the structure characteristics, which assist in enhancing nucleation of the gas bubbles, subsequent coalescence, and facilitated departure from the surfaces. / QC 20100924

The use of solid polymer electrolytes in lithium-ion batteries has the advantage in terms of safety and processability, however they often lack in terms of performance. This is of major concern in applications where high current densities or rapidly changing currents are important. Such applications include electrical vehicles and energy storage of the electrical grid to accommodate fluctuations when using renewable energy sources such as wind and solar. In this study, the use of commercial poly(vinyl alcohol) (PVA) as a solid polymer electrolyte for use in lithium-ion batteries has been evaluated. Films were prepared using various lithium salts such as lithium bis(trifluoromethane)sulfonimide (LiTFSI) and casting techniques. Solvent free films were produced by substituting the solvent Dimethyl sulfoxide (DMSO) with water and rigouros drying or by employing a hot-pressing technique. The best performing system studied was PVA-LiTFSI-DMSO, which reached ionic conductivities of 4.5E-5 S/cm at room temperature and 0.45 mS/cm at 60 °C. The solvent free films showed a drop of ionic conductivity by roughly one order of magnitude compared to films with residual DMSO present. High ionic conductivities in PVA-LiTFSI-DMSO electrolytes are thus ascribed to fast lithium ion transport through the liquid domain of DMSO, or by plasticizing effects of salt and solvent on the polymer. Thermal analysis of the films showed a clear plasticizing effect of DMSO by a decrease in the glass transition temperature. FTIR analysis showed complexation of all the lithium salts investigated with the OH-groups of the polymer by a shift in the characteristic frequencies of both salts and polymer. For the first time, prototype battery cells containing PVA electrolytes were manufactured and evaluated by galvanostatic cycling. PVA-LiTFSI-DMSO showed stable cycling performance for 15 cycles. Solvent free electrolytes were also investigated but did not result in any stable cycling performance.

Drug delivery systems (DDS) with multiple functionalities such as environment-sensitive drug release mechanisms and visualization agents have motivated the biomedical community as well as materials chemists for more than a decade. This dissertation is concerned with the development of nanoparticles for multifunctional DDS  to tackle several crucial challenges in these complex systems, including polymeric nanospheres which respond to temperature change, superparamagnetic iron oxide nanoparticles/polymeric composite for magnetic resonance imaging contrast agents and drug carriers, immunoresponse of nanomaterials and injectable magnetic field sensitive ferrogels. The biocompatible and biodegradable polylactide (PLA) was employed as matrix materials for polymeric nanosphere-based DDS. The thermosensitive polymeric nanospheres have been constructed through a “modified double-emulsion method”. The inner shell containing the thermosensitive poly(N-isopropylacrylamide) (PNIPAAm) undergoes a “hydrophilic-to-hydrophobic” phase transition around the human body temperature. The sensitivity of the polymer to the temperature can facilitate drug release at an elevated temperature upon administration. In addition, gold nanoparticles were assembled on the dual-shell structure to form a layer of gold shell. The cell viability was found to be enhanced due to the gold layer. The immunoresponse of the gold nanoparticles has been considered even if no acute cytotoxicity was observed. Imaging is another functionality of multifunctional DDS. This work focuses on magnetic resonance imaging (MRI) and involves synthesis and surface modification of superparamagnetic iron oxide nanoparticles (SPIONs) for contrast agents. The SPIONs have been prepared through a high temperature decomposition method. Surface modification was carried out in different ways. Poly(L,L-lactide) (PLLA) was grafted on SPIONs through surface-initiated ring-opening polymerization. The hydrophobic model drug indomethacin was loaded in the PLLA layer of the composite particles. For biomedical applications, it is essential to modify the hydrophobic particles so that they can be dispersed in physiological solutions. A series of protocols including using small charged molecules and amphiphilic polymers has been established. Pluronic F127 (PF127), a triblock copolymer was applied as a phase transfer reagent. Most interestingly, PF127@SPIONs show remarkable efficacy as T2 contrast agents. The PF127@SPIONs have been successfully applied to image the cochlea in a rat model. As another phase transfer reagent, poly(maleic anhydride-alt-octadecene)-graft-PNIPAAm (PMAO-graft-PNIPAAm) was created for surface modification of SPIONs. This new copolymer provides the modified SPIONs with thermosensitivity together with water-dispersibility. As another form of DDS, ferrogel made of PF127 copolymer and SPIONs was developed. Gelation process depends on the temperature of the SPIONs/PF127 mixture. This property makes it possible to use the ferrogel as an injectable drug carrier. Unlike other ferrogels based on crosslinked polymeric network, the PF127 ferrogel can entrap and release hydrophobic drugs. Application of an external magnetic field is found to enhance the drug release rate. This property can find application in externally stimulated local drug release applications. / QC20100722

The tribo system ice-curling stone was investigated in order to understand the mechanisms behind the stones' behavior on the ice sheet. The problem with non-identical stones should also be addressed.The stone curls, that is, its sliding path deviates from a straight line to the right for a clock-wise rotation and to the left for a anti-clock-wise rotation. Several mechanisms to explain this behavior have been proposed over the years but none has been successful.By carrying out experiments at the local curling rink and studying silicon castings of ice- and stone-surfaces with scanning electron microscopy and vertical scanning interferometry, it has been decided that the curl is not due to dry friction, ice-debris or the difference in friction on the left and right side of the stone. The side force comes from the fact that the friction is higher at the back of the stone than at the front.The contact between stone and ice is never completely dry, nor in the hydrodynamic lubrication regime. It is probably a combination of hydrodynamic lubrication and a contribution from mechanical scratching of the ice. The coefficient of friction depends upon the velocity, from 0.01 for velocities around 1 m/s to higher values for lower velocities. It is not possible to make identical stones, that is identical glide band structures out of Blue Hone granite, since its composition is too inhomogeneous and its grain size is too course. It is recommended to use an amorphous or very fine grained material, at least in the surface of the glideband.

Ferroelectric liquid crystals (FLCs) are being investigated as alternatives to nematic liquid crystals in display applications due to their low power requirements and fast switching times. Commercial FLCs consist of a chiral dopant in an achiral smectic C (SmC) liquid crystal host. A bulk property that arises from the chiral nature of this mixture is a spontaneous polarization (PS), which depends on the polarization power of the chiral dopant (δp). The magnitude of δp reflects the ability of a dopant to induce a polarization in an achiral host. It has been proposed that the magnitude of δp can be enhanced by matching dopant and host structures, which may enhance the propagation of chiral perturbations from the dopant to the host. This is known as the chirality transfer feedback (CTF) model. Previous studies in the Lemieux lab featured 2H NMR to detect chiral perturbations exerted by a dopant on the liquid crystal host based on the observation of pairs of quadrupolar doublets in the 2H NMR spectra. In the work described herein, the contribution of chirality transfer feedback to the difference in quadrupolar splitting between pairs of quadrupolar doublets (ΔΔνQ) was assessed by 2H NMR spectroscopy. These experiments confirmed the results reported by Finden and Yuh by demonstrating the presence of chiral perturbations exerted by a diester substituted 6,6’-spirobiindandione dopant ((RS)-2.6-d4) on the achiral SmC host NCB76, and the absence of those perturbations using the diester substituted 5,5’-spirobiindandione analogue ((RS)-2.3-d4). Subsequent studies explored the effect of modifying the chiral topography of the 2,2’-spirobiindan-1,1’-dione core on the magnitude of δp. Both the 5,5’- and 6,6’-disubstituted cores were reduced to give the corresponding mono-carbonyl derivatives ((R)-3.4-d4 and (R)-3.8-d4), substituted with ether side-chains. Finally, ester side-chains were added to the 6,6’- mono-carbonyl derivative ((R)-3.9-d4) for comparison with previous experiments. The ferroelectric induction properties of these dopants were investigated in NCB76 at mole fractions ranging from xd = 0.03 – 0.10. The mono-carbonyl 5,5’- and 6,6’-diether dopants gave absolute polarization powers of 120 nC/cm2 and 123 nC/cm2 respectively, which are not significantly different. This suggests that a reduction in the chiral topography of the spirobiindandione core greatly affects the polarization power of the dopant and may reduce the contribution from chirality transfer to δp. This was confirmed by a measurement of the polarization power of the 6,6’-diester mono-carbonyl dopant (R)-3.9-d4 in NCB76, which gave a δp value of 117 nC/cm2. / Thesis (Master, Chemistry) -- Queen's University, 2008-07-11 15:10:53.56

During energy generation, transportation and usage, large amounts of energy are lost as waste heat. With increasing energy consumption and environmental issues, exploiting this waste heat has drawn extensive attention. Thermoelectric energy conversion is an approach to take advantage of the ability of thermoelectric materials to convert waste heat into electricity. The thermoelectric effect was initially studied in the early 19th century with the discovery of the Seebeck effect. Thermoelectric materials and devices can directly convert thermal energy (temperature gradients) into electric energy (voltage) and vice versa. Thermoelectric devices have been used in space as energy generators and as coolers in small-scale instruments and devices. However, thermoelectrics remain limited in terms of applications. The traditional state-of-the-art thermoelectric materials, such as Bi2Te3, PbTe, and SnTe, exhibit high thermoelectric properties, but their disadvantages of toxicity, extreme rarity of tellurium, and oxidation when exposed to high temperature air restrict them from widespread use in applications. Compared to traditional thermoelectric materials, misfit-layered Ca3Co4O9 not only has the typical advantages of oxides including low cost, being environmentally friendly, and good chemical stability at high temperatures, but also has relatively high thermoelectric properties due to the complex structure which composed of CoO2 conductive layers and rock-salt type Ca2CoO3 insulating layers. Many strategies have been used to enhance the thermoelectric performance of Ca3Co4O9. Compared with bulk materials, thermoelectric thin films can exhibit improved thermoelectric properties and new application in flexible devices and miniaturization. Flexibility can be induced in Ca3Co4O9 by nanostructural tailoring to act as fully inorganic flexible thermoelectrics. In order to explore how to produce Ca3Co4O9 nanoporous thin film and control the porosity in the films, I have investigated the nanoporous Ca3Co4O9 system. Nanoporous Ca3Co4O9 thin films were synthesized using sequential reactive magnetron sputtering and post annealing to determine the key factors of nanoporous Ca3Co4O9 formation and tailoring of the porosity. / Under produktion, transport och användning av energi förloras stora mängder som spillvärme. Med ökande energiförbrukning och miljöfrågor har utnyttjande av spillvärme fått mer uppmärksamhet de senaste åren. Termoelektrisk omvandling av energi är ett tillvägagångssätt som utnyttjar förmågan hos termoelektriska material att omvandla spillvärme till el. Den termoelektriska effekten studerades ursprungligen i början av 1800-talet med upptäckten av Seebeck-effekten. Termoelektriska material och enheter kan direkt omvandla termisk energi (temperaturgradienter) till elektrisk energi (spänning) och vice versa. Termoelektriska komponenter har använts i rymden som energikällor och för kylning i småskaliga instrument och anordningar. Emellertid förblir termoelektriska komponenter begränsade när det gäller breda tillämpningar. Traditionella termoelektriska material som Bi2Te3, PbTe och SnTe, har bra termoelektriska egenskaper, men deras nackdelar med toxicitet och oxidation när de utsätts för luft vid hög temperatur begränsar dem från utbredd användning, liksom det faktum att råmaterialet tellur är mycket sällsynt. Jämfört med traditionella termoelektriska material har Ca3Co4O9 inte bara de typiska fördelarna med oxider som låg kostnad och kemisk stabilitet vid höga temperaturer utan har också relativt goda termoelektriska egenskaper på grund av den komplexa strukturen som består av ledande CoO2-skikt och isolerande Ca2CoO3-skikt. Många strategier har använts för att förbättra dess termoelektriska prestanda. Termoelektriska tunna filmer kan uppvisa förbättrade termoelektriska egenskaper och leda till nya tillämpningar i flexibla enheter och miniatyrisering. Mekanisk flexibilitet kan induceras i Ca3Co4O9 genom att styra nanostrukturen. För att utforska hur man producerar Ca3Co4O9 tunna filmer och kontrollerar porositeten i filmerna har jag undersökt det nanoporösa Ca3Co4O9-systemet. Nanoporösa tunna Ca3Co4O9 filmer syntetiserades med sputtring för att bestämma de viktiga faktorerna som påverkar bildning och porositet i Ca3Co4O9-filmer. / <p>Funding agencies: Chinese Scholarship Council, The Knut and Alice Wallenberg Foundation, The Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linköping University (Faculty Grant SFO-Mat-LiU No. 2009 00971), The Swedish Energy Agency (Project 46519-1)</p>

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The work presented in this thesis focuses on how to utilize epitaxially grown graphene on SiC as a basis for ultra-sensitive gas sensor. Several approaches have been tested and evaluated to increase the sensitivity, selectivity, speed of response and stability and of the graphene based gas sensors with a focus on air quality monitoring applications. The graphene surfaces have been functionalized with different metal oxide nanoparticles and nanolayers using hollow-cathode sputtering and pulsed laser deposition. The modified surface was investigated towards its topography, integrity and chemical composition with characterization methods such as AFM, Raman and XPS. Moreover, the binding energy was calculated with density functional theory for benzene and formaldehyde when reacting with pristine epitaxial graphene and iron oxide nanoparticle decorated graphene to verify the usefulness of this approach. The impact of environmental influences such as operating temperature, relative humidity and UV irradiation towards sensing properties was investigated as well. To further decrease time constants, the first-order time-derivative of the sensor’s resistance is introduced as an alternative sensor signal and evaluated towards its applicability. Applying these methods in laboratory conditions, sensors with a quantitative readout of single ppb benzene and formaldehyde were developed and time constants of less than one minute could be achieved with the first-order time-derivative signal. These results show promise to fill the existing gap of low-cost but highly sensitive and fast gas sensors for air quality monitoring.

Epoxy resins are used in a number of different industries and therefore have application-specific material requirements, from satellites that require materials that operate in space, to paints and coatings that require high scratch resistance and mechanical durability, to medical devices, designed to be in continuous contact with biological fluids. Commercial epoxy products come with manufacturer’s information explaining the epoxy properties and recommended preparation processing conditions, which may include epoxy resin to curing agent mix ratio (Part A : Part B), cure time, and cure temperature, for example. Due to proprietary reasons, it can be difficult to understand why these values are provided, and more importantly, the consequences when deviating from the prescribed recommendations. When manufacturing bioprocessing products for the medical field, a company is under a limited capacity to change materials of construct. Determining how to modify the processing conditions in order to control the material properties of an epoxy would benefit bioprocessing product manufacturers as it would allow them to use the same epoxy that meets the different application-specific requirements of different products. Five different epoxy systems that were designed for medical applications were characterized to determine how variations in preparation and processing conditions, such as mix ratio (by weight) and cure conditions, affect the final properties of the cured epoxy, including: glass transition temperature, chemical resistance, and coefficient of thermal expansion. For each system, it was found that one mix ratio would produce a material with a maximum glass transition temperature, while changing the mix ratio with either excess Part A epoxy resin or excess Part B amine curing agent would result in a decrease in the glass transition temperature. A higher glass transition temperature indicates higher crosslink density, as a more tightly crosslinked network requires more thermal energy to reach the “rubbery” phase. This mix ratio did not always coincide with the manufacturer’s specifications, suggesting that these recommendations are potentially application specific. While variations in the curing agent’s chemical composition impacted the final material properties of epoxy, as expected, it was also found that varying the mix ratio and annealing conditions resulted in changes in epoxy material properties. A wide range of experiments provided critical data that supported the idea that a single epoxy formulation can be used to produce epoxy materials with varied performance properties through modifications in the preparation and processing conditions, while still remaining usable to manufacture products.