Determination of the relative sensitivity of polyaniline inks and films to deprotonation by ammonia using UV–Vis spectroscopy

Abstract

The deprotonation behavior of conducting polymers such as polyaniline (PANI) is an important functional parameter in the design of novel printed electronic devices, particularly for sensors and energy storage. PANI can be fabricated into films from precursor liquid-processable ‘ink’ formulations. The effective determination and comparison of the deprotonation behavior of such inks is critical to understanding their subsequent functional performance. While protonation can be measured by titration with protonating and deprotonating agents using UV–vis spectroscopy, comparative analysis has proven challenging due to complexities in the measurement of polymer concentration and consequent lack of comparability. This work introduced a coherent approach to establishing the arbitrary concentration of PANI ink formulations. Dodecylbenzene sulfonic acid (DBSA)-micellar doped PANI nanoparticles suspended in sodium dodecyl sulfate were prepared using various monomer, oxidant, and dopant ratios, titrated with ammonia and analyzed using UV–vis spectroscopy. Isosbestic points unaffected by doping or protonation state were used to establish arbitrary polymer concentration. Similar titrations on films prepared from these formulations were performed using ammonia in the gas phase and were based on calculations of deposited mass. Parameters such as a ‘doping capacity’, and their relative sensitivity to ammonia could be determined, which could in turn be related to the physical and chemical compositions of the resulting inks and films. The developed methodology has the potential to be a simple and convenient means with which to compare and optimize the functional deprotonation behavior of conducting polymer inks and films for device development and production optimization.