Colloidal cluster phases and solar cells

The arrangement of soft materials through solution processing techniques is a topic of profound importance for next generation solar cells; the resulting morphology has a major influence on construction, performance and lifetime. This thesis investigates the connections between the soft matter physics of colloidal systems and solid state dye sensitised (SSDS) and bulk heterojunction (BHJ) solar cells. A study of aqueous titanium dioxide nanoparticulate suspensions was carried out in order to observe how suspension structure can be controlled by altering the inter-colloid potential via pH-induced electrostatic charging. Measurements were performed at volume fractions between 0.025% and 8.2% with the solution pH set to 3.1, 3.5 or 4.5 before mixing. Suspensions with a volume fraction above 4% formed self-supporting gels regardless of the set pre-mix pH. These gels displayed shear thinning behaviour with a power law exponent of 0.8, a yield stress of 11(1) Pa and rheological response consistent with an aggregated fractal network. At lower volume fractions, suspensions exhibited consolidation interpreted as the collapse of a gel of fractal clusters with a fractal dimension of 2.36. The velocity of the suspension/supernatant interface exhibited delayed sedimentation behaviour, as well as further fractal-based power law scalings with volume fraction. Lower volume fraction suspensions were explored using dynamic light scattering. Limited aggregation of ‘stable’ suspensions was observed when compared to primary aggregate radii measured from electron microscopy images. To connect suspension structure and cell manufacture, the behaviour of more concentrated suspensions was observed during the drying of thin films, a process which forms an essential part of a SSDS solar cell. Lowering the pH of the suspension after mixing from 4 to 3 resulted in an ordering of observed crack domains. An increase in film delamination was also observed. Rates of mass loss during drying followed the expected three phase process, although there was an unexpected increase in rate during the initial phase (where rate is usually constant in time). Dynamic light scattering was found to be a useful but demanding technique for studying cluster formation in titanium dioxide suspensions. A non-linear fitting technique utilising the method of moments was thoroughly explored using computer simulated datasets. The algorithm reduced the systematic error in fitted parameters for moderately polydisperse (0:2 < < 0:4) datasets as compared to the commonly applied linear algorithm. The fitting algorithm was also robust to bad initial estimates of parameters. Finally, test solar cells have been built using blends of titanium dioxide and poly-3-hexylthiophene. Device performance was reduced with blend standing time after mixing but could be improved by remixing the blend before spin coating, implicating a reversible process (e.g. aggregation of titanium dioxide or crystallisation of P3HT) in the loss of performance. Addition of a titanium dioxide hole blocking layer before spin coating reduced cell performance. Combining the above studies and these device designs provides a future platform for continuation of this work in the context of real devices

Thermochronology, landscape evolution and hydrogeology of the Katonga Valley in south west Uganda

The reversed river systems of south west Uganda attracted geoscientists to study the geomorphology of the region in the mid 20th century. During the succeeding fifty years the population and GDP per capita have both risen between five and six fold with a consequent increase in water demand. This thesis aims to apply modern quantitative techniques and theoretical developments to improve our understanding of the landscape evolution of the Katonga Valley and contribute to the groundwater resource assessment of associated alluvial deposits. Karoo-age glaciogenic strata were discovered filling the western valley. Subsequent apatite fission track analyses reveal that the currently exposed rocks were reheated to a temperature consistent with over 2 km of burial during the Mesozoic. Therefore, it is inferred that the western River Katonga has preferentially eroded a Gondwanan paleovalley exhumed from beneath the former sedimentary cover. Electrical resistivity tomography of the valley fill has identified three broad cycles of erosion and deposition, including: 1) The Gondwanan palaeovalley with indurated glaciogenic strata; 2) The Neogene relict valley with fluviolacustrine sediments; and, 3) The late Quaternary channel and with recent wetland deposits. Downwarping of the Victoria Basin in the east produced the first drainage divide on the originally westward flowing River Katonga during the middle Pleistocene. Downthrow of the George Basin in the west led to rejuvenation of the western landscape prior to the formation of a second drainage divide due to rift flank uplift. Sand and gravel associated with an old denuded landscape survives in terraces above the water table in the central valley. Variable climate and fluctuating lake levels led to the deposition of fluviolacustrine deposits in the eastern valley. Pumping tests in this silty sand indicate that the transmissivity is almost always adequate for village water use and is sometimes commensurate with town water supplies

Nutritional quality and digestibility of maize hybrid plants for silage. Life sciences in dialogue of generations: connections between universities, academia and business

In order to assess the silage potential of maize hybrids, the nutritional quality and the enzymatic in vitro digestibility of five local maize hybrids (ZP 707, ZP 7357, ZP 7072, ZP 7777, and ZP 6263) was tested in the laboratory of the Group for Food Technology and Biochemistry of the Maize Research Institute "Zemun Polje". The hybrids were grown at a total of four locations, one in Srem (Autonomous Province of Vojvodina) and three in Central Serbia. The hybrid 7001 was used as a standard. The selection of hybrids for this research was made on the basis of the actuality of individual hybrids and the market orientation of the Maize Research Institute. The following properties were investigated: dry matter content, lignocellulose fiber content, and in vitro dry matter digestibility of the whole plant. According to the achieved results, it can be concluded that hybrids ZP 707, ZP 7357, followed by ZP 7777 proved to be the maize genotypes highly preferable for the production of silage. All tested hybrids achieved better results than the standard in most locations. Hybrid ZP 707 on average had the highest in vitro dry matter digestibility (61.43 ± 1.86%), as well as the lowest content of all lignocellulosic fibers (NDF-52.76%, ADF-24.40%, ADL-2.58, hemicellulose-28.36, and cellulose-21.82%), which all indicates its potential as a silage maize form suitable for cultivation in different agro-ecological conditions. In terms of digestibility and dry matter content, the ZP 707 hybrid can be singled out as the most stable, i.e. it is appropriate for growing both in lowland areas and at higher altitudes. ZP 6263 proved to be the most inferior hybrid at most locations, while based on in vitro digestibility and dry matter content, ZP 7072 hybrid varied the most. The digestibility of the whole plant was negatively affected by the higher content of primarily lignin (ADL), followed by ADF and cellulose fraction share. Although it is optimal to harvest silage maize in the waxy maturity stage of grain ripeness, when the dry matter content of the whole plant is in the range between 30 and 35%, the harvest time in some hybrids in some locations was significantly exceeded, which affected the results of dry matter digestibility. The findings obtained in this study can be highly useful for future breeding programs directed toward creating new and improved silage maize hybrids

Southern Accent September 2001 - May 2002

Southern Adventist University\u27s newspaper, Southern Accent, for the academic year of 2001-2002.https://knowledge.e.southern.edu/southern_accent/1079/thumbnail.jp