Probing the extent of the Sr{sup 2+} ion condensation to anionic polyacrylate coils: A quantitative anomalous small-angle x-ray scattering study
- Institut fuer Festkoerperforschung, Forschungszentrum Juelich, Postfach 1913, D-52425 Juelich (Germany)
The shrinking process of anionic sodium polyacrylate (NaPA) chains in aqueous solution induced by Sr{sup 2+} counterions was analyzed by anomalous small-angle x-ray scattering. Scattering experiments were performed close to the precipitation threshold of strontium polyacrylate. The pure-resonant scattering contribution, which is related to the structural distribution of the Sr{sup 2+} counterions, was used to analyze the extent of Sr{sup 2+} condensation onto the polyacrylate coils. A series of four samples with different ratios [Sr{sup 2+}]/[NaPA] (between 0.451 and 0.464) has been investigated. From the quantitative analysis of the resonant invariant, the amount of Sr cations localized in the collapsed phase was calculated with concentrations v between 0.94x10{sup 17} and 2.01x10{sup 17} cm{sup -3} corresponding to an amount of Sr cations in the collapsed phase between 9% and 23% of the total Sr{sup 2+} cations in solution. If compared to the concentration of polyacrylate expressed in moles of monomers [NaPA], a degree of site binding of r=[Sr{sup 2+}]/[NaPA] between 0.05 and 0.11 was estimated. These values clearly differ from r=0.25, which was established from former light scattering experiments, indicating that the counterion condensation starts before the phase border is reached and increases rather sharply at the border.
- OSTI ID:
- 21024342
- Journal Information:
- Journal of Chemical Physics, Vol. 127, Issue 15; Other Information: DOI: 10.1063/1.2787008; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-9606
- Country of Publication:
- United States
- Language:
- English
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