Conductivity of polyelectrolyte solutions containing mono‐and divalent counterions

Abstract

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).

Osmotic pressure in polyelectrolyte solutions: cell-model and bulk simulations

“…The single-chain cell model gives a larger slope at higher concentrations than the corresponding simulation of 8 chains in a periodic box for a 16mer, but the two simulation approaches give more or less the same result for a 256mer, which is beyond the long-chain limit of the simulations (see Section 3.5). Considering this limit, our simulations can be said to confirm the general conclusion that simulations give higher values of the osmotic coefficient than experiments, 6,10,12,16 as discussed in the Introduction.…”

“…19 Comparisons to experimental values have been made for simulations of stiff chains and a general trend is that the simulations give higher values of the osmotic coefficient. 6,10,12,16 The difference is not always large and can sometimes be removed by adjusting the simulation parameters, 12 but Antypov and Holm got significantly higher values, which could not be explained by any known deficiency of the model. 16 Arh et al showed that for various experimentally measured polyelectrolytes, the osmotic coefficient does not approach 1 as the linear charge density goes to zero; i.e., there is a contribution to the non-ideality that is not due to electrostatic interactions.…”

“…5 To gain additional insight, the osmotic pressure of polyelectrolyte solutions have also been calculated by simulations for both flexible and stiff chains. [6][7][8][9][10][11][12][13][14][15][16][17][18][19] Most studies have been for salt-free systems, but some have considered the effects of added salt. 16,18,19 It is generally argued that the counterions give the main contribution to the osmotic pressure from the polyelectrolyte, but Chang and Yethiraj took a different view when they focused on the excess part of the osmotic coefficient and stressed the importance of the polyion-counterion interactions in a salt-free system 14 and also pointed to non-negligible polymerpolymer contributions in a study including salt.…”

Counterion Activity of Highly Charged Strong Polyelectrolytes

“…In addition, most of experimental work has been carried out at concentrations too high to be considered highly diluted, 29,30,36,37,42,45,47,48 hence preventing rigorous model discrimination. Furthermore, the water quality often did not correspond to that required for salt-free conditions.…”

Molecular mass and ionic strength dependence of electrochemical properties of flexible polyelectrolytes

“…However, often the disagreement between experiment and theory results from the fact that the experimental conditions were incompatible with assumptions from theoretical considerations. For example, the concentration region was far from being highly diluted [I1 -181, the water quality did not correspond to "salt free" conditions [13,[18][19][20][21], the samples had high polydispersity with parts of relatively short chains [21, 221, respectively. In principle, the strong increase of the equivalent conductivity and the maximum which was experimentally found in some cases at high dilution [19, 231 are not predicted by the existing theories.…”