Hydration of polyions

Most of the ion-exchange resins consist of polyions. A typical one is also the most well known Nafion, the structure of which is shown in Fig. 2.77 the figure also shows the structure of some proteins (these are often polyelectrolytes). 

In aU these structures the interaction of the solvent with the polyelectrolyte is critical for its stability (cf. Fig. 2.4). The ion concerned is usually nonspherical and a more typical configuration is cylindrical, as with the linear polyphosphates. 

the ionizing group in many of these materials is in the side chain, as with polyacrylic acid [Fig. 2.77(e)]. Correspondingly, in the linear polyions there are structures of the kind shown in Fig. 2.77(c) and (d). 

---

Zundel reports on the hydration of thin polyelectrolyte ion-exchange membranes subject to progressive increases in water sorption. Spectroscopic observations of these systems reflect the hydration of polyion charge centers in the membranes but in the presence of associated counterions, which in turn are progressively hydrated. Zundel worked with polysulfonates and found the spectra of unhydrated polymer salts the cation is attached unsymmetrically to the SOj groups. This mode of attachment leads to a loss of degeneracy in the antisymmetric vibrations. 

---