Osmotic pressure of polyelectrolytes without added salt

Abstract

We have applied scaling theory to published data on the osmotic pressure II of solutions of the polyelectrolytes sodium poly(styrenesu1fonate) (NaF'SS) and poly(styrenesu1fonic acid) (HPSS) without added salt. The data cover 4 decades of polymer concentration C; molecular weights M range from 20 to 1060 K. Three different concentration regimes are observed. In the low concentration regime, Jl depends on molecular weight. In the semidilute regime, scaling predictions are accurately obeyed: II is independent of M, and the slope of II vs C is 1.125. In this regime, the dependence of II on C also agrees well with predictions of the Poisson-Boltzmann cylindrical cell model theory, though only if the linear charge spacing used in the calculations is somewhat less than the structural value. A dramatic increase in osmotic pressure is observed in the concentrated regime. The slope of II vs C is close to 2.25, the value predicted from scaling theory for semidilute neutral polymer solutions. This suggests that polyelectrolytes may adopt an expanded random-coil chain conformation in highly concentrated solutions without added salt.

Thermodynamic study of aqueous solutions of polyelectrolytes of low and medium charge density without added salt by direct measurement of osmotic pressure

“…In contrast to the results communicated in that work it was not possible to fit linear functions to our experimental data indicating that the exponent q in the proportionality P $ c q m;2 is not constant but it is dependent on the mass concentration. Its average value (1.12 ± 0.06) was close to the theoretical one (1.125) [31].…”

“…In order to test this concept the osmotic pressure of solutions of all sodium salts and pure PVA as a function of mass concentration are shown in figure 8 in the form of double logarithmic plot. A test of the scaling concept was published earlier for osmotic pressure of salt free aqueous solutions of polystyrene sulfonic acid (HPSS) and its sodium salt (NaPSS) in a wide range of concentration and molar mass [31]. In contrast to the results communicated in that work it was not possible to fit linear functions to our experimental data indicating that the exponent q in the proportionality P $ c q m;2 is not constant but it is dependent on the mass concentration.…”

Ratio of Moduli of Polyelectrolyte Gels in Water With and Without Salt

“…This indicates that the 8 of the ionized polyacrylamide is at most equal to 1.08 for NaAc concentration higher than 2 mol%, or the exponent n is at most equal to 1.4 (assuming m=l/3). This number apparently is approaching the theoretical result of n=1.12 [19]. It is worth pointing out that it takes only a very low concentration of ionic groups on the network to make the network behave like a polyelectrolyte one.…”

“…Recently Wang and Bloomfield [19] have successfully applied the renormalization group theory to study semidilute polyelectrolyte solutions, such as poly(styrene sulfonate). They found that the existing experimental results agree well with theoretical predictions given by equations (22) Given these polyelectrolyte solution results, it is interesting to see how the corresponding polyelectrolyte gels behave.…”

On the nature of influence of polyelectrolyte molecular weight on aniline electropolymerization

“…Indeed, some authors [27][28][29][30] established enhanced counterion condensation by HMW polyelectrolyte. More efficient counterion condensation leads to lower effective charge of macromolecule chain, and as a result, the higher the molecular weight of polyelectrolyte, the more coiled conformation it has [27,31]. Obviously, this difference is eliminated in the presence of strong background electrolyte.…”