Polyaniline: Factors affecting conductivity and mechanical properties

The main objectives of this study were: (a) to study electronic and mechanical properties of films of the conducting polymer, polyaniline, in the doped and undoped emeraldine oxidation state. (b) to study how the electronic and mechanical properties were modified through mechanical stretch-orientation of the films. (c) to study the effect of water vapor on the conductivity of stretched protonic acid doped films. (d) to observe changes in tensile strength and Young\u27s modulus when selected plasticizers were introduced into the films. (e) to observe, using UV/Vis spectroscopy, the effect that neutral salts in the doping media have on the doping level of thin, optically transparent films of polyaniline. (f) to use thin, optically transparent films to spectroscopically study (by UV/Vis) hysteresis in the doping and undoping behavior of polyaniline. The significant results and conclusions are: (a) mechanical stretch-orientation of polyaniline increased the tensile strength of emeraldine base films from $\sim$54 MPa (unstretched) to $\sim$124 MPa (four-fold elongation). (b) the conductivity of doped films of polyaniline was increased approximately two orders of magnitude by stretch-orientation (four-fold elongation) from $\sim$5 S/cm to $\sim$90 S/cm. (c) an increase in the relative percent crystallinity (by x-ray diffraction) upon stretch-orientation of emeraldine base films; this persisted after doping (HCl). (d) the removal of water vapor was found to decrease the conductivity of stretched (four-fold elongation) emeraldine.HCl films from $\sim$204 S/cm at 15 mm to $\sim$22 S/cm at 0 mm of P$\sb{\rm H2O}.$ (e) both tensile strength and Young\u27s modulus are decreased by the introduction of plasticizers and dopant plasticizers into the films. (f) no loss in conductivity was observed due to the addition of plasticizers. (g) the presence of neutral salts in the doping media increased the doping level of thin films of polyaniline; this was attributed to Donnan equilibrium effects at the polymer/solution interface. (h) observed hysteresis upon doping and undoping thin polyaniline films is due to irreversible morphological changes that take place in polyaniline upon doping and undoping