The electrospinning of blended polyaniline nano-fibres and their application in an ion-selective electrode

Polyaniline (PAni) is a conducting polymer that has shown promise in the field of composite sensors, including ion-selective and biomedical sensors. Sub-micron fibres of PAni/poly(vinyl chloride) (PVC) and PAni/poly(acrylonitrile) (PAN) have been electrospun from THF/DMF and DMSO/DMF respectively. Quaternary ammonium salts (QAS) were incorporated into these polymer blends in an attempt to produce electrospun solid-state conducting polymer ion-selective electrodes for the detection of nitrate in aqueous solutions. The electrospinning process relies on a number of different parameters for successful fibre production, including solution viscosity, solution surface tension and solution conductivity. The role of these parameters on the electrospinning of PVC from THF/DMF solution and PAN from DMSO/DMF solution, both with and without the addition of PAni and QAS, was studied. In addition to this study, the morphology of the resultant fibres was determined by Scanning Electron Microscopy (SEM). SEM morphology and fibre-sizing analysis revealed significant changes in the morphological properties of the electrospun fibres, including bead formation and alteration of the fibre diameters with varying solution viscosity, solution surface tension and solution conductivity. It is believed this is the first time that the influences of the conducting properties of PAni on these essential electrospinning parameters have been documented. Electrospun fibrous mats of conducting and non-conducting blends, in addition to blends incorporating QAS were analysed by Raman spectroscopy to determine the degree of doping of PAni, the influence of QAS on the chemical properties of the electrospun fibres and also the degree of dispersion of PAni throughout the electrospun fibres. PAni was found to be relatively well dispersed throughout the underlying fibre mat. Raman spectra of PAni/PAN electrospun fibres indicated that PAN influenced the doping of PAni significantly. It produced characteristic peaks similar to those observed in the 'secondary doping' of PAni associated with increases in free-charge carriers and changes in the PAni chain conformation. This phenomenon also occurred for PAni/PVC electrospun fibres in the presence of the QAS, tetradodecylammonium bromide (TDAB) and triallylethylammonium bromide (TAEAB). It is believed that this is the first time that 'secondary doping' of PAni was induced by the normally electro-inactive species PAN or TDAB. If this is so, it indicates a strong interaction between PAni and these species which is not based on the use of dopant solvents for 'secondary doping'. Mechanical strength measurements of electrospun fibres of these polymer blends were also carried out, indicating that the support polymer, the degree of orientation and also the components of the polymer blend significantly influence the tensile strength of these materials. However the overall tensile strength of these samples was relatively low compared with literature values for other electrospun fibres. Cyclic voltammetry (CV) analysis of electrospun composite PAni fibres showed that PAni retains its electroactivity and produced the characteristic oxidation/reduction responses expected of PAni. It is believed that this is the first time electrochemical responses have been recorded for fibres electrospun from PAni/PVC and PAni/PAN blends. Amperometric responses for nitrate, chloride and tetrafluoroborate were observed, indicating that whilst these fibre mat electrodes were sensitive to changes in solution composition, they were not selective towards nitrate in solution, regardless of the QAS employed.