School of Chemistry - Theses
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ItemSolid-state thin films solar cells on polymer substrates( 2015)To meet the world’s ever-growing energy needs while facing current environmental challenges, solid-state thin film solar cells offer a low-cost renewable alternative for generating electricity. Polymer substrates give thin films lightweight and flexibility, broadening their potential applications to consumer electronics and power-generating textiles. The use of solution processable materials on flexible substrates paves the way towards roll-to-roll printing of photovoltaics, taking advantage of available, low-cost manufacturing technologies. However, constructing efficient solar devices on plastic substrates remains difficult due to the substrate’s intrinsic low-temperature limitation. Furthermore, the stability of thin films needs to be addressed in order for them to become viable candidates for commercial applications. In the first research Chapter, volatile liquid electrolytes were replaced with composite polymer electrolytes to improve the stability of dye-sensitized solar cells (DSCs). On one hand, the infiltration of viscous electrolytes through the TiO2 working electrode was suspected to constitute a major limitation to producing efficient flexible devices. On the other hand, the temperature restriction of polymer substrates prevented the sintering of mesoporous TiO2 directly onto these substrates. Therefore, submicrometer-sized mesoporous TiO2 beads, that can be treated prior to the device fabrication, were investigated as a potential route to overcome the aforementioned issues. Efficient quasi-solid-state DSCs were successfully fabricated on plastic substrates, and studies on the infiltration of the electrolyte through the electrode were conducted. Then, efforts were focused on photovoltaics utilizing inorganic-organic perovskites, an emerging technology with reported efficiencies rivalling existing commercial solar cell technologies. Solution processed, these hybrid materials can be prepared at low temperature, thus becoming a potential candidate for application to polymer substrates. Nevertheless, the majority of these solid-state devices constructed on glass employ a high temperature processed inorganic hole blocking layer (≥450 °C), non-compatible with flexible applications. In this regard, efforts were directed towards the development of methods to fabricate efficient flexible solid-state perovskite devices on polymer substrates with a range of low-temperature processed hole blocking layers. As a result of the moisture and temperature sensitivity of these hybrid perovskites, a perovskite deposition method was developed and optimized, in order to improve the reproducibility of these devices. In Chapter 4, power conversion efficiencies (PCEs) over 13 % were attained for TiO2-based flexible planar perovskite devices, with an average efficiency of 11.8 ± 1.8 %. In Chapter 5, ZnO was chosen as an electron selective material given its advantages for printing, and PCEs over 10 % were achieved for spin-coated ZnO-based perovskite solar cells on polymer substrates. Exacerbated degradation of CH3NH3PbI3 was observed when deposited on ZnO, therefore the correlation between the annealing conditions and the decomposition of the perovskite film was examined. In Chapter 6, practical industrial concerns such as the stability and the manufacturing processability of these devices were considered. PCEs over 10 % were obtained for flexible perovskite devices with a printed TiO2 layer, but the device reproducibility was affected by the fabrication protocol. Finally, the stability of TiO2-based perovskite devices on polymer substrates was assessed, and encapsulation of flexible devices was performed to extend the device lifetime. To understand the origins of the degradation of CH3NH3PbI3-based solar devices, a range of storage conditions was used, and their impacts on the perovskite film were investigated. The following research questions will be addressed throughout the thesis: -Is the infiltration of the electrolyte through the TiO2 film critical? -Can the low temperature processing restriction on polymer substrates be overcome by developing a low temperature inorganic blocking layer synthesis? -Can solid-state solar cells on polymer substrates be made commercially viable? -What are the parameters that affect the degradation of CH3NH3PbI3-based perovskite solar cells?
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ItemInterfacial effects on aqueous sonochemistry and sonoluminescence( 1999-06)The dissolution of quantum sized CdS and MnO2 particles in water was conducted using 20 kHz ultrasound. CdS particles were found to dissolve chemically via an oxidation process while MnO2 particles dissolved via a reductive process. It was found that the dissolution of the colloids could be controlled via the addition of surface active chemicals to solution and by varying the saturation gas type. In the presence of Na2S or propan-2-ol and argon gas, the dissolution of CdS was inhibited, whereas the addition of alcohols (methanol, ethanol, propan-2-ol, butan-1-ol and pentan-1-ol) to the MnO2 system led to an increase in the amount of dissolution for a given time of sonication. This increase in dissolution was found to be dependent on the ability of the surface active radical scavenger to accumulate around the bubble interface during the cavitation process. Eventually, at higher alcohol concentration there was a plateau or a limiting value reached for the efficiency of colloid dissolution which was common for each alcohol. (For complete abstract open document)
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ItemInterfacial tension study and rheological characterisation of water-in-oil emulsion explosives( 2007)Highly concentrated emulsion explosives are complex colloidal systems that remain robust for very many years after production. In this work a poly-isobutyl succinic anhydride (PIBSA) derived emulsions have been studied to understand the extraordinary nature of the stability and flow of these emulsions. In this study a model sodium oleate emulsion system is developed to further confirmation of the nature emulsion explosives. Two PIBSA based emulsifiers were used to prepare the emulsions. The main emulsifier of interest was comprised of an amide, ester and imide head group attached to a PIBSA chain, the second was entirely comprised of an imide head group attached to a PIBSA chain. The pendant drop method was used to obtain dynamic interfacial tension measurements for an interface between of paraffin oil/PIBSA-imide and ammonium nitrate, and dodecane/sodium oleate and sodium nitrate. The IsoFit-WardTordai computer package that incorporated Langmuir, Frumkin, Reorientation and Aggregation adsorption isotherms was used to calculate diffusion coefficients for total time adsorption. Diffusion coefficients for short time adsorption with Langmuir and Frumkin isotherms were determined and long time adsorption with the Langmuir isotherm were calculated. All of the diffusion coefficients results suggested that direct diffusion controlled adsorption was not the mechanism these surface active agents employed, rather, the results suggested that an activation barrier controlled adsorption process dominated the kinetics of the interfacial adsorption. There is much evidence to suggest that rheological properties of highly concentrated emulsions have not been characterised correctly for some time. This is mainly due to wall depletion or wall slip effect phenomenon inherent to rheological investigations performed on smooth stainless steel surfaces. The effect of wall slip was eliminated through physical means by performing rheological investigations with a sand blasted cone and plate, and the use of the vane geometry as a rheomter. Another method to eliminate wall slip effects in steady shear for highly concentrated emulsions was formulated and established in this investigation. A two-stage Tikhonov regularisation procedure that converts steady shear data into rheological property functions has been developed. The two-stage method is able to obtain not only the shear-stress shear-rate function but also the slip velocity as a function of wall shear- stress. The method is such that it obtains the rheological functions over the maximum range of shear-rate covered by the data. The results obtained using the new method were compared to those obtained using the sand blasted cone and plate and vane geometry with good agreement being observed. Over a 17 month period, a PIBSA based emulsion was observed in order to determine if any dramatic rheological changes were taking place with time, the results obtained in both shear and dynamic analysis effectively concluded that the PIBSA emulsion explosive was extremely stable and the minor changes observed were within experimental uncertainty of the measurements. Various microscopy techniques were used to determine the droplet structure and size distribution within various emulsions. Optical microscopy, Qualitative Phase Imaging, Differential Interference Contrast imaging were employed, and it was found that the PIBSA and PIBSA-imide emulsions had a spherical shape rather than a hexagonal close packed structure that was previously assumed for these emulsion explosives. Images of the sodium oleate emulsion indicated that there were obvious destabilising mechanisms at work, affecting the longevity of the emulsion.
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ItemCubic phase lipids as novel biosensing surfaces( 2011)Sub-micron particles, called cubosomes, formed from the fragmentation and steric stabilization of inverse bicontinuous cubic phases (QII) of lipids have a microenvironment reminiscent of biological lipid bilayers, making them promising class of material for a number of applications. The phase behaviour of the amphiphile phytantriol (3,7,11,15-tetramethyl-1,2,3-hexadecanetriol) is well characterised and we describe studies of cubosomes formed from the QII phase of phytantriol/water systems. Cubosomes tailored for specific applications require additional components, which can alter the structure and phase behaviour of the system, for example the incorporation of ligands such as a receptor lipid or protein for biomedical applications. Hence, a study of the effect of additives on the phase behaviour of cubosomes was undertaken. Data obtained using the small-angle X-ray scattering (SAXS) beam line at the Australian Synchrotron showed that addition of non-functional amphiphiles to the matrix of phytantriol/water cubosomes affected the lattice parameter of the cubosomes and, hence, the cubosome microstructure. Oleic acid and monoolein stabilized the Pn3m cubic phase of the cubosomes, whilst CTAB and SDS caused a loss of structure at lower temperatures/molar concentrations of additive. Synchrotron SAXS was also used to investigate the effect of functional additives, the ganglioside receptor, GM1, and the biotinylated phospholipid, bDSPE, on the matrix of the phytantriol/water cubosomes. The results of these studies indicated that both systems would yield stable double diamond Pn3m cubosomes at low – medium molar concentrations of additive. To further investigate the viability of these systems for biomedical and biosensing applications we screened their binding capacity against their natural ligands. Using a combination of enzyme-linked immunosorbent assay (ELISA), surface plasmon resonance (SPR), and quartz crystal microbalance (QCM) techniques, we showed that GM1 containing cubosomes specifically bind to cholera toxin (CT) with an IC50 of 1.6 nM, which is more potent than any currently available inhibitor. Specific targeting of bDSPE containing cubosomes to avidin-modified surfaces was visualised using cryogenic transmission electron microscopy (cryo-TEM), as was the ability of surface-bound bDSPE cubosomes to specifically bind ligands from solution. Further QCM results demonstrated how bi-functionalised cubosomes, containing GM1 and bDSPE, could be targeted to a surface via one functionality, then sense a secondary ligand via a separate functionality. The results presented in this thesis provide insight into the effect of additives on the phase behaviour of cubosome systems and factors, which affect their potential biomedical and biosensor applications.