The activity and mobility of the counterions in strong polyelectrolyte solutions are considerably smaller than in simple electrolyte solutions of the same concentration in basemol dm-3, a fraction of the counterions being apparently bound to the highly charged polyions l). The theoretical studies of polyelectrolyte solutions containing a mixture of mono-and divalent counterions2-4) give rise to the conclusion that the fraction of bound counterions is higher for divalent counterions, and that the extent of binding of both ionic species increases with increasing the fraction of monovalent ions. This conclusion seems to be verified by several experimental investigations -8) of various thermodynamic properties. In this work an attempt has been made to examine the influence of counterion binding on the apparent ionic mobility and conductivity of such solutions. For this purpose the electrical conductivity of mixed solutions containing poly(styrene-p-sulfonic acid), (HPSS)c), or poly(ethy1enesulfonic acid), (HPES)d, and the corresponding magnesium salt was measured as a function of the degree of neutralization at constant concentration of the polymer. The results are interpreted in the light of the cell model of polyelectrolyte solutions l). Experimental PartPoly(sodium styrene-p-sulfonate), (NaPSS)C), having an average molecular weight of about 4. 104 was kindly supplied by the Dow Chemical Co., while the poly(sodium ethylenesulfonate), (NaPES)C), was prepared in this laboratory according to the procedure of Breslow and Kutner9). With both polymers the degree of substitution was found to be l,O. The polyelectrolyte was purified by dialysis and converted to the acid and to its magnesium salt by ion exchange. The conductivity of (H/Mg)PSS solutions at concentrations 0,0075, 0,02, and 0,05 basemol . dm-3 and of (H/Mg)PES at 0,005 and 0,Ol basemol . dm-3 with the degree of neutralization, NMp+ + = 1 -N H + , equal to O,O, 0,2, 0,4, 0,6, 0,8 and 1,0 was measured by a Jones conductivity bridge (Leeds & Northrup Co.). Distilled water of electrolytic conductivity below a) Presented at the 27th International Symposium on Macromolecules, Strasbourg 1981. b, Permanent address: Faculty of Natural Sciences, University of Brno, 61137 Brno, Czechoslovakia. ' ) Systematic IUPAC nomenclature: HPSS: poly[l-(4-sulfophenyl)ethylene]; HPES: poly(1sulfoethylene); NaPSS: poly[sodium 1-(4-sulfonatophenyl)ethylene]; NaPES: poly(sodium 1 -sulfonatoethylene).
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