Faculty of Natural and Agricultural Sciences
School of Physical Sciences
Department of Physics
Selected Highlights from Research Findings
The brightly metallic-coloured scarab beetle, Gymnpleurus virens, which is mainly found in southern Africa, reflects almost entirely left circularly polarised light – the only known example of this phenomenon in nature. Scientists in the Department of Physics discovered the reason for this asymmetrical preference. The beetle’s shell consists of many layers of microfibrils aligned parallel to each other, with each layer rotated slightly relative to the layer above. This forms a helicoidal stack twisting in the left direction, which then causes left circularly polarised light to be reflected. The colour of the beetle is determined by the thickness of the layers, and defects in the structure broaden the reflectance band. These results may find practical applications in the fabrication of nano-engineered chiral reflectors used in display and laser technologies
Contact person: Prof DJ Brink.
Silk has been used as a textile for more than 3 000 years and as a biomedical suture material for centuries, but in the second half of the 20th century it was replaced by new synthetic fibres with highly reproducible properties. Today there is a renewed interest in natural polymers as biotechnological and biomedical resources because of their unique properties, which include non-toxicity, biodegradability and biological compatibility. In collaboration with the research group of Dr Philippe Colomban in Paris, France, the research group used micro-Raman spectroscopy to study the changes that occur in silk fibres during the application of stress, as structural changes at the molecular level will influence the performance of the fibres in any application. Silk consists of proteins in helical, random coil and anti-parallel b-sheet structures. The properties of the silk (elasticity and strength) depend on the relative amounts of configurations present, as well as the amino acid sequence of the protein backbone. Under stress, helical coils are transformed into b-sheets. If the stress increases, the fibre breaks. The researchers chose to study the silk of the domestic silkworm, Bombyx mori, used for sericulture, the wild South African and Namibian silkworms, Gonometa rufobrunea and Gonometa postica, and the spider silk from Madagascar, Nephila madagascariensis, as this provided them with the opportunity to compare the results of two well-characterised silk fibres, Bombyx mori and Nephila, with unknown silk from the Gonameta species. They found significant differences between degummed and untreated silk fibres of different origins, which will be helpful in choosing between silks for different applications
Contact person: Ms LC Prinsloo.
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