Scanning Electron Microscopy for Nano-morphology Characterisation of Complex Hierarchical Polymer Structures

This thesis presents novel and innovative ways of imaging and analysing natural hierarchical polymers using low-voltage scanning electron microscopy and secondary electron energies. Materials such as plant fibres, feathers and silk, have received increased societal and scientific interest recently, while the plastic industry is faced with growing public concerns over its generation of waste, and use of petrochemical precursors. In nature, materials are produced sustainably and they furthermore exhibit inspiring mechanical performance. One such material is spider silk, which is spun at room temperature from a water-based protein gel to form a thread, which even with diameters as small as 5 μm easily suspends the weight of a palm-sized spider. It is known that the secret to spider silk’s remarkable properties lies within its nanoscale structures. However, the direct observation of these nanostructures has remained difficult due to their small size and their sensitivity to chemical and mechanical alteration. This work presents novel sample preparation protocols and demonstrates their use in accessing size and location information of key nanostructures within spider silk through nanoscale observation in the scanning electron microscope. As the secondary electron spectroscopy technique employed here is relatively new, new workflows from sample preparation, over optimal imaging and spectral acquisition and novel multivariate data analysis techniques are innovated and described in detail. The rigorous consideration of the material and method are exemplified on a feather section, to show that the secondary electron energy signal in the scanning electron microscope may generate molecular composition maps on a proteinaceous structural polymer. This work lays out all requirements for unlocking the vast potential for nanoscale chemical mapping which lies in the nanoscale secondary electron signal, to further inspire ground-breaking studies into the nanostructures of complex hierarchical polymers.