Ion Conduction in Solid Polyelectrolyte Complex Materials

This chapter describes the progressmade in understanding themechanisms of ion conduction in polyelectrolyte complexes (PEC). Understanding of ion dynamics is based on frequency-dependent conductivity data obtained by impedance spectroscopy as a function of temperature, hydration, and composition. In most of the work, strong polyelectrolytes such as poly(alkali 4-styrene sulfonate) (AlkaliPSS) and poly(diallyldimethyl ammoniumchloride) (PDADMAC) are employed, forming complexes of type xAlkaliPSS (1 - x) PDADMAC. The dc conductivity is always determined by the alkali ions, which exhibit a size-dependent mobility. This holds even in PEC with an excess of PDADMAC. The ion dynamics and transport mechanisms are different in PDADMAC-rich and in NaPSS-rich PEC. We review the treatment of the frequency-dependent shape of conductivity spectra by scaling concepts and by models involving forward-backward hopping motions of small ions as well as localized motions of charges. Thus, many quantitative concepts established in other disordered ion conductors can be transferred to PEC. In addition to the well-known time-temperature superposition principle (TTSP), the novel concept of time-humidity superposition (THSP) was established for PEC and describes the dependence of ion dynamics on water content.