Fabrication and applications of fluorescent polymer fibres
This thesis studies the manufacture, and properties, of semiconducting polymers in fibrous (cylindrical) geometries and their use in applications such as explosives sensing and as luminescent concentrators. The main method of fabrication used in this thesis is electrospinning. A method was developed to manufacture ordered arrays of nanofibers through the use of a static parallel plate system alongside a top plate. This method was found to produce fibres with greatly increased order parameters compared to those from a flat collection plate. Narrower gaps between the plates resulted in higher order parameters due to increased anisotropy in the transverse electric field. A custom substrate was also developed to collect ordered arrays of suspended nanofibers. Fibres produced through electrospinning have been used as fluorescent explosives sensors. Polystyrene fibres containing m-MTDATA were found to improve sensing efficiencies over films with thinner fibres producing the highest efficiencies due to an improved surface-area-to-volume ratio. Furthermore, the least dense samples were found to give the highest sensitivities. Intrinsic semiconducting fibres of ADS125GE and F8BT supported these findings but their sensing efficiency demonstrated a strong dependence on PLQY. The development of electrospinning recipes for a range of materials are detailed in this thesis. Polystyrene fibres, doped with either Rhodamine B or polyfluorene, have been produced; Rhodamine B doped fibres were successfully deposited from DMF while the polymer blends required mixed solvents. Suspended PVK fibres have been collected through the use of a custom substrate from mixed DMF:toluene solutions. Superyellow fibres with secondary structures have been collected from chlorobenzene and TBAH solutions. Luminescent concentrators have been developed with cylindrical geometries filled with dye or polymer solutions. Two propagation loss mechanisms have been identified; with a fast initial loss attributed to untrapped light, then a slower decay due to self-absorption and other loss processes. These structures exhibited concentration ratios in the region of 20-50.
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