The concentration dependence of the self-diffusion coefficients of strontium ion in aqueous polystyrenesulfonic acid solutions

The diffusion coefficients of strontium in 10−4M aqueous solutions of polystyrenesulfonic acid were measured at 26°C. The coefficients were low, about 0.15 X 10−5 cm.2/sec., until strontium equivalent to one‐fifth of the sulfonates had been added. They then increased relatively rapidly, to about 0.7 X 10−5 cm.2/sec., as the concentration of strontium was increased to 10−4M. These results are interpreted to mean either that the binding of counterions to a polyelectrolyte is limited to parts of a chain and is not related to the chain as a whole, or else that there is a recurring regularity of structure in the atactic polystyrene sulfonic acid which limits binding of counterions to a fraction of the total charged sites.