Thermodynamic Characterization of Rare Earth Salts of Strong Polyacid Copolymers
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- 作者：Judit Horvá ; th ; Mikló ; s Nagy
- 刊名：Journal of Physical Chemistry B
- 出版年：2007
- 出版时间：May 17, 2007
- 年：2007
- 卷：111
- 期：19
- 页码：5140 - 5148
- 全文大小：196K
- 年卷期：v.111,no.19(May 17, 2007)
- ISSN：1520-5207
文摘
Stoichiometric La3+, Ce3+, and Nd3+ salts of poly[(vinyl alcohol)-co-(vinyl sulfate)] (PVAS) copolymerpolyacids have been studied in aqueous solution without added salt. All LnPVAS salts were entirely water-soluble in the composition and concentration range investigated. Ratios of the vinyl sulfate and vinyl alcoholunits in the copolymers were between 1:5 and 1:107, leading to structural charge densities both above andunder the critical value needed for counterion condensation of trivalent counterions. Solvent activity, a1, hasbeen measured by the gel deswelling method in the concentration range of 5 × 10-4 to 1 × 10-1 mol ofcounterion/kg of water (0.2-9 w/w% of the polyelectrolyte). Results are unusually high for polyelectrolytes(-2 × 10-6 > ln a1 > -3 × 10-4), and they are comparable with values determined in solutions of unchargedpolymers. Nevertheless, the different copolymers can be clearly distinguished; the water activity is loweredin the order of the vinyl sulfate content of the polyelectrolytes, except for the one above the critical chargedensity. No observable difference was caused in the thermodynamic properties by the different lanthanidecounterions. Reduced osmotic pressure curves and Flory-Huggins pair interaction parameters have beencalculated; both of them were used to estimate degrees of dissociation at zero as well as at finite concentrations.Degrees of dissociation are decreasing with increasing concentration or vinyl sulfate content of the copolymer.They take values between 8-36% at zero polymer concentration and they reach zero value simultaneouslyat ~1 × 10-3 mol of polymer chains/kg of water. The average number of released counterions per polymerchain (DPn = 1005) approaches to a limit of about 4.4 with increasing vinyl sulfate content. This correspondsto average charge distances of b 
19 nm and charge density parameters of 
0.037. The latter is, however,a very low value and indicates a 1/9 contraction compared to the rod-like assumption.
19 nm and charge density parameters of 0.037. The latter is, however,a very low value and indicates a 1/9 contraction compared to the rod-like assumption.