9 - Experimental Methods

Abstract

This chapter reviews several experimental methods used to characterize perfluorinated ionomers. Polymer precursors, sulfonyl fluoride, and carboxylic ester can be hydrolyzed using solutions of sodium or potassium hydroxide. Fluorinated cation exchange polymers can be stained by cationic dyes. In staining the cross-sections of films, slicing or microtoming must be done before staining. Sulfonyl fluoride precursor form can undergo reactions with many reagents; they include reactions with ammonia or amines. In ion exchange equilibrium, the concentration of ions in the polymer phase requires somewhat arbitrary assumptions of the volume of electrolyte occupying the polymer phase. The Donnan theory describes the distribution of anions and cations between the polymer phase and an external electrolyte. If a cation-selective membrane separates solutions of different compositions, the cations in the two solutions readily exchange within the requirement of electrical neutrality. For instance, trace quantities of cations in a very dilute solution can be extracted and concentrated into a more concentrated acid solution. The effect is driven by the tendency of the hydrogen ions in the more concentrated solution to diffuse into the dilute solution. This creates a Donnan potential that forces the other cations in the opposite direction.