Abstract
For the perfluorocarboxylate polymer membrane-aqueous electrolyte systems, the dependence of the membrane volume on the types of counter ions was investigated. As the counter ions, alkali metal ions (Li+, Na+, K+, Rb+, Cs+) and. H+ ion were used. From the relation of the specific volume of the membrane to the water content, the volume of hydrophilic region in the membrane was estimated. For the membrane of the forms of alkali metal ions, the volume of hydrophilic region in the microheterogeneous membrane structure was found to be in the same order as for the size of the ion cluster for the perfluorosulfonated membrane. Taking into account the microheterogeneous structure of the membrane, the counter ion concentration in the membrane and the molar volume of the counter ion were calculated for each type. It was suggested that the difference in the volumes of hydrophilic region among several counter-ion types was mainly attributed to the volume behavior of counter ions in the hydrophilic region and that ionic molar volume within the membrane is nearly equal to that in the aqueous solution for types of relatively high water content.
