Effect of the polymer characteristics on ion binding

The extent of ion binding depends on a number of characteristics of the polyion degree of dissodation, acid strength, conformation, distribution of ionizable groups and cooperative action between these groups (Wilson Crisp, 1977 Oosawa, 1971 Harris Rice, 1954, 1957). The hydration state of the macromolecule, which is in turn dependent on conformation, also affects ion binding (Begala, 1971). 

The strength of ion binding is enhanced when the arrangements of the functional groups permit chelate formation (Begala Strauss, 1972). Thus, magnesium is more firmly bound to poly(vinyl methyl ether-maleic acid) than to either poly(acrylic acid) or poly(ethylene maleic add). 

When the degree of neutralization is small the charge on the polyion and the number of counterions will also be small and the majority of counterions will be free. As the degree of neutralization, a, increases, the polyion charge, Q, will increase. This observation follows from the following equations  

The solvation (hydration) and desolvation of ions is important to the gelation process in AB cement chemistry. The large dipole moment of ion-pairs causes them to interact with polar molecules, including those of the solvent. This interaction can be appreciable. Much depends on whether the solvent molecule or molecules can intrude themselves between the two ions of the ion-pair. Thus, hydration states can affect the magnitude of the interaction. The process leading to separation of ions by solvent molecules was perceived by Winstein et al. (1954) and Grunwald (1954). 

Consider two ions in contact. As they are pulled apart the potential energy of the two ions increases. At some critical point the separation becomes sufficient for a polar solvent molecule to occupy the space between them, which reduces the energy of the system. Further separation increases the energy of the system again. These changes demonstrate that two types of ion-pair exist contact and solvent-separated. 

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