Melanins are a class of bio-macromolecules that are found throughout the biosphere. They fulfill various functions in human beings, which makes them a long studied substance in medicine and biology. Furthermore they possess a set of rare and special physico-chemical properties which include featureless broad band absorption in the UV-Vis spectrum and condensed phase electrical conduction. Many scientists have interpreted their findings in terms of an amorphous semiconductor model, but this was done under the a priori assumption that charge transport in melanin is electronic. However, a very strong dependence of melanin’s electrical properties on its level of hydration has recently led to speculations that the dominant charge carrier for high hydration is of protonic rather than electronic nature. This thesis will present direct evidence for electronic charge transport, found by investigating the influence of different environmental parameters on the conductivity of melanin. It will furthermore be shown that the hydration dependent conductivity of melanin can be understood in terms of a dielectric response model for an amorphous semiconductor. This establishment of the major charge carrier is an important step in the on-going effort to fully map the structure-property relationship of melanin and will help to understand its function in vivo. With the ultimate goal to make use of melanin’s fascinating properties, thin films, a new class of device has been characterized and investigated. These thin films, while exhibiting melanin’s characteristics, show improved mechanical stability, a very uniform morphology and a much faster response than standard pellet samples. They are furthermore applicable to standard polymer processing techniques which brings technological applications within reach.
| Identifer | oai:union.ndltd.org:ADTP/254066 |
| Creators | Johannes De Boor |
| Source Sets | Australiasian Digital Theses Program |
| Detected Language | English |
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