Transport properties and ion binding in aqueous solutions of alkali metal salts of poly(thiophen-3-ylacetic acid)

Abstract

Aqueous solutions of poly(thiophen-3-ylacetic acid) neutralized with LiOH, NaOH, and CsOH were for the first time investigated using conductivity measurements (in concentrations, c, ranging from 2·10−5 to 8·10−2mol/dm3 and temperatures from 278.15 to 313.15K), transport number measurements (at 298.15K) and osmotic coefficient measurements using vapor pressure osmometry (at 313.15K) and cryoscopy, in order to identify essential electrochemical characteristics of this conjugated polyelectrolyte. The measurements of the polyion constituent transport number data suggested that a fraction of counterions traveled associated with polyions. The fraction of “free” counterions, determined from the transport measurements by the association theory of Huizenga, Grieger, and Wall was around 0.5, which is in good agreement with the osmotic coefficient data. Neither the fraction of “free” counterions, nor the osmotic coefficient significantly depends on the nature of the counterion species. The results obtained were analyzed in terms of the Poisson–Boltzmann theory, Manning's condensation approach, and modern scaling theory. Good agreement between the theoretical results and the fraction of “free” counterions, determined from the combination of the transport number and conductivity measurements, was obtained. The osmotic coefficients were well reproduced by the Poisson–Boltzmann cell model theory.