Research Case Studies - Materials Laboratory
Tip-Enhanced Raman Spectroscopy
The characterisation of nano-materials is crucially important for the burgeoning nanotechnology and biomaterials fields and, in particular, where these fields merge. Conventional optical spectroscopy is diffraction limited resulting in, at best, lateral resolutions of 200-400 nm when using visible light sources, while materials are being produced well below that size.
Tip-enhanced Raman scattering spectroscopy (TERS) is an emerging tool for investigating such systems – revealing chemical information with nanoscale spatial resolution.
TERS is a combination of scanning probe microscopy (SPM) and Raman spectroscopy. TERS utilises the surface enhancement of the Raman signal and spatially confines it to an enhancement region around an SPM tip. In the Vibrational Spectroscopy & Chemical Imaging Group laboratories, this is achieved by coating commercially available AFM tips a suitably enhancing metal substrate (typically gold or silver). The metal-coated tip is then brought into close proximity with a sample (by SPM feedback mechanisms) and aligned with a focused laser spot. Thereafter, rastering the sample allows TERS maps to be obtained which reveal spatially resolved chemical information about the system under study.
Using the TERS approach Sergei Kazarian's group has been able to discriminate carbon nanotubes of different types from within a mixture. They have also applied this technique in the “upright mode” to spatially resolve a bundle of carbon nanotubes in a configuration which can be applied to the study of opaque samples. Current research within the group is focused on revealing nanoscale chemical information across a range of nano-patterned surfaces and nanomaterials. TERS is currently also applied to studying nanostructures of graphene in collaboration with the Department of Chemistry.
Bacterial Cellulose Enhanced Natural Fibre-Polymer Matrix Interface
Steadily increasing oil prices and the public’s growing awareness of a sustainable future have sparked and revived the research and development of 'green materials'. Unfortunately, the mechanical performance of these green materials is often inferior compared to traditional materials, as is the case when comparing renewable and petroleum-based polymers. The Polymer and Composite Engineering (PaCE) group has been working on combining natural fibres with these inferior renewable polymers to create fibre-reinforced polymer composites that match or even exceed the performance of commonly used engineering materials.
However, the tendency of natural fibres to expand when heated and shrink when cooled (see figure) often results in poor natural fibre-polymer matrix interface. To overcome this problem, cellulose produced by bacteria (also known as bacterial cellulose) serves as an interesting alternative for the design of renewable composites that overcomes the aforementioned poor fibre-matrix interface. Bacterial cellulose is inherently nano-sized with diameter of approximately 50 nm and several micrometres in length.
By culturing bacteria in the presence of natural fibres, nano-sized bacterial cellulose is preferentially deposited onto the micro-metre sized natural fibres. This approach allows us to manufacture bacterial cellulose-reinforced, natural fibre-reinforced truly green hierarchical composites that overcome the poor fibre-matrix interface via mechanical interlocking.
The PaCE group has also devised a cost-effective method to create hierarchical structures within composites by utilising bacterial cellulose as binder for the otherwise loose natural fibres. This is achieved by using a papermaking process, whereby a dispersion of bacterial cellulose and natural fibres is filtered and the wet filter cake is pressed and dried. The resulting rigid and robust natural fibre preform can be resin infused with a renewable resin to produce randomly oriented bacterial cellulose-reinforced, natural fibre-reinforced hierarchical composites that possess mechanical performance that exceed the neat polymer and conventional fibre-reinforced polymer composites, respectively.