Cyclic temperature dependence of electrical conductivity in polyanilines as a function of the dopant and synthesis method

Abstract

Most of the studies dealing with polyanilines (PANIs) are focused on electrochemical polymerization; however, chemical polymerization is more suitable for large–scale production. In order to develop commercially viable, clean, effective materials for thermal sensor devices, temperature dependent electrical response has been studied in PANIs obtained by simple, low-cost synthesis conditions, transferable to industrial processing. PANIs doped with HCl, dodecylbenzene sulfonic acid (DBSA) and sodio-5-sulfoisophtalic acid (NaSIPA) were prepared by chemical oxidative polymerization, through direct and indirect routes of synthesis. TEM images disclosed formation of nanorods and microfibrils. Microstructural analysis confirmed differences in doping level and crystallinity which were related with the PANI conductivity.

Two PANI-DBSA synthesized by direct and indirect methods, exhibit the best conductivity retention up to 150 °C. In cyclic tests, they show excellent performance after 4 heating-cooling cycles up to 70 °C. The amplitude of electrical response for PANI-DBSA obtained by direct synthesis is twice the value of PANI-DBSA prepared by indirect route. Conversely, the latter displays slightly better repeatability due to its lower moisture content. This study suggests that both PANI-DBSA are suitable for use in electronic applications, under ambient conditions below 150 °C, and are promising materials for temperature sensor applications.