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ION–SOLVENT INTERACTIONS 191

Fig. 2.77. Ion-exchange resins. a = nafion; b = the Asahi structure similar to nation’s;
c = polyimines; d = polyphosphates; e = polyacrylic acid; f = polymethacrylic acid; g =
polyvinylpyridine; h = polysterene sulphonic acid.
In all 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.
Thus, 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).

2.23.2. Volume of Individual Polyions
To obtain the partial molar volume of a series of poly vinyl acid salts containing
a cation of tetraalkylammonium, one plots the volume V of the total electrolyte against
and obtains the partial molar volume by extrapolating the volume of the anion.
Such volumes are given in Table 2.29.

2.23.3. Hydration of Cross-Linked Polymers (e.g., Polystyrene
Sulfonate)

It is possible to study step-by-step hydration of biomolecules as was first done by
Gluckauf. The hydration is localized and connected to ionic binding. Thus, Gregor et
al. found that the order of adsorption onto polystyrene was