Ion-Exchange Resin Swelling

The real swelling behavior of cross-linked ion-exchange resins immersed in electrolyte solutions of varying concentrations denote that these systems can be considered as a charged 

The Physical Chemistry of Materials Energy and Environmental Applications 

Swelling can also be understood as the internal solution of the ion-exchange resin, and then the system can be treated as a concentrated solution (the polymeric resin) in osmotic equilibrium with a more diluted solution (the exchange solution) [4], 

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Ion-exchange resins swell in water to an extent which depends on the amount of crosslinking in the polymer, so that columns should be prepared from the wet material by adding it as a suspension in water to a tube already partially filled with water. (This also avoids trapping air bubbles.) The exchange capacity of a resin is commonly expressed as mg equiv./mL of wet resin. This quantity is pH-dependent for weak-acid or weak-base resins but is constant at about 0.6-2 for most strong-acid or strong-base types. 

Dry ion exchange resins swell when they are added to water, and the volume of the beads is further dependent upon the nature of the cation present. The equilibrium state represents a minimization of... 

As already indicated, ion exchange resins are osmotic systems which swell owing to solvent being drawn into the resin. Where mixed solvent systems are used the possibility of preferential osmosis occurs and it has been shown that strongly acid cation and strongly basic anion resin phases tend to be predominantly aqueous with the ambient solution predominantly organic. This effect (preferential water sorption by the resin) increases as the dielectric constant of the organic solvent decreases. 

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