A conductivity study and calorimetric analysis of dried poly(sodium 4-styrene sulfonate)/poly(diallyldimethylammonium chloride) polyelectrolyte complexes

Abstract

Ionically cross-linked polyelectrolyte complexes (PECs) of anionic poly(sodium 4-styrene sulfonate) (PSS) and cationic poly(diallyldimethylammonium chloride) (PDADMAC), xPSS.(1-x)PDADMAC, with molar fractions x ranging from 0.30 to 0.70, were prepared and subsequently dried. The PEC samples were analyzed by differential scanning calorimetry, and the ionic conductivity sigmadc of the samples was measured as a function of temperature by means of impedance spectroscopy. The thermograms display an endothermic peak in the temperature range of 90-143 degrees C, which is attributed to a glass transition of the PEC. The glass transition temperature Tg has a symmetric x dependence with a minimum at x=0.50. The temperature dependence of sigmadcT is not affected by the glass transition. The ionic conductivity of the samples before drying is three orders of magnitude larger than sigmadc after drying; nevertheless, their activation enthalpies are identical. Arrhenius parameters obtained from the systematic study of several PEC compositions are discussed. The ionic conductivity of the PSS-rich samples is significantly higher than sigmadc of PDADMAC-rich samples. This implies a relatively high Na+ mobility as compared to Cl(-) mobility in PEC. In contrast to the symmetric x dependence of Tg, the conductivity of PEC increases and the activation enthalpy decreases with increasing x in the investigated composition range. A strong x dependence of sigmadc is observed for PSS-rich PEC, which is attributed to a significant variation in the mobility of the charge carriers.

Mechanisms of Ion Conduction in Polyelectrolyte Multilayers and Complexes

“…2 of Ref. [31]. During the first scan we observed a large endothermic peak with an onset temperature between 41…”

“…These are summarized in Ref. [31]. This large peak is absent in the following runs and can, therefore, be attributed to the evaporation of water which is still present after freeze-drying of the PEC.…”

“…All complexes were formed from solutions of reagent grade chemicals by precipitation, dialysis and freeze drying; the procedure is described in Ref. [31]. The preparation of CsPSS by ion exchange of freeze-dried NaPSS is explained in Ref.…”

“…The data base contains impedance spectra of different polyanion/polcation combinations in multilayers in dependence on humidity and impedance spectra of PEC as a function of composition and temperature [19,31,32,36]. Analyzing the data, we discuss the relevance of the contributions of different ionic species, such as the alkali cations, anions, or protons to the conductivity.…”

“…Furthermore, systems with mainly one type of counterion can be prepared, when excess salt is removed by dialysis. In this way conductivity data in dependence of the composition can be related to the conductivity contribution of a single type of charge carrier [31,32]. For this purpose solid PEC complexes have to be prepared by drying and pressing.…”