Abstract
AbstractThe adiabatic compressibility of a 1:1 copolymer of styrene and maleic acid and its 50% and 100% neutralized sodium salts in aqueous solution was determined by sound velocity and density measurements at 25°C. Similar to poly(acrylic acid) and its salts, the apparent molal adiabatic compressibility and volume of this poly(dibasic acid) and its two sodium salts were found to be concentration independent. In the 100% neutralized copolymer the electrostrictive effect was highest and accordingly the lowest ΦK (−100,0·104 cm3 bar−1 mol−1) and ΦV (140,3 cm3/mol) values were obtained. By suppression of dissociation of the counter ions in NaCl solution (c = 1 mol/dm3), the magnitude of electrostriction was somewhat reduced and accordingly ΦK and ΦV increased to −46,0·10−4 cm3 bar−1 mol−1 and 161,6 cm3/mol respectively. The ΦK and ΦV values were resolved into their ionic components ΦK and ΦV. It was observed that the ionic volume of the macroions decreased progressively with increase of degree of neutralization. The electrostriction, caused in the copolymer by an increase of negative charge from 0 to −1 and from −1 to −2, produced a decrease of 11 and 182 cm3/mol in ΦV. Contrary to the volume change, the compressibility data showed a considerable decrease in the case of 50% neutralized product, but no further change was observed in 100% neutralized copolymer. The viscosity data also showed a similar behaviour. This was explained as being due to the strong bond of the sodium ions in the nucleus by the highly charged anionic groups reducing the charge effect considerably.
Published Version
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