This thesis explores the use of X-ray photoelectron spectroscopy (XPS) for characterising the bio-stability of polyaniline (PANI) films in biomedical applications. PANI has gained increasing interest in the literature due to its tuneable conductivity and variable oxidation states.
There exist significant challenges for PANI. It is required to remain stable a high pHin order to avoid the loss of conductivity, due to the dopant leaching out from the polymer backbone. The first aspect of the thesis utilised XPS as an analytical technique to elucidate this phenomenon. Two types of dopant were selected to chemically dope the polyaniline-emeraldinebase (PANI-EB), followed by thin film fabrication by the spincoating technique. Results from XPS reveal that deprotonation occurs in response to the incubation in physiological conditions. The loss of dopant was observed, and is in agreement with previous findings. Additional methods of characterisation such as ToF-SIMS and UV-Vis were conducted, which support the findings of the XPS measurements.
Since instability could lead to the impaired conductive function of PANI in biomedical applications, a suitable dopant ought to be explored. In the second project, a patch comprising of a bilayer film was fabricated. During the manufacturing process, a polymerised PANI was grown on a chitosan layer, with phytic acid (PA) as a dopant. XPS was again used to characterise the surface stability. The patch was found to be stable for up to 14 days, as the dopant signals remained detectable. Depth profile analysis showed that the PA not only works as the dopant, but also crosslinked the PANI and chitosan layers.
High pressure XPS (HPXPS) has been performed as an advanced technique to reveal the surface chemistry of PANI film at elevated pressure, in a water environment, in an attempt to measure surface chemistry under realistic conditions. To the best of our knowledge this is the first report of a conducting polymer film specifically PANI, measured using HPXPS.
Collectively, XPS has been used as a primary tool in understanding the surface chemistry of the PANI surfaces and the designated bilayer system.