Shrinking of anionic polyacrylate coils induced by Ca2+, Sr2+ and Ba2+: A combined light scattering and ASAXS study
- 196 Downloads
Anionic polyacrylate chains (NaPA) form precipitates if alkaline earth cations are added in stoichiometric amounts. Accordingly, precipitation thresholds were established for three different alkaline earth cations Ca2+, Sr2+ and Ba2+. Close to the precipitation threshold, the NaPA chains significantly decrease in size. This shrinking process was followed by means of combined static and dynamic light scattering. Intermediates were generated by varying the ratio [MCl2]/[NaPA] with M denoting the respective alkaline earth cation. All experiments were performed at an inert salt level of 0.01M NaCl. Similar coil-to-sphere transitions could be observed with all three alkaline earth cations Ca2+, Sr2+ and Ba2+. Based on these findings, supplementary conventional and anomalous small-angle X-ray scattering experiments using selected intermediates close to the precipitation threshold of SrPA were performed. The distribution of Sr counterions around the polyacrylate chains in aqueous solution provided the desired scattering contrast. Energy-dependent scattering experiments enabled successful separation of the pure-resonant terms, which solely stem from the counterions. The Sr2+ scattering roughly reflects the monomer distribution of the polyacrylate chains. Different ratios of the concentrations of [ SrCl2]/[NaPA] revealed dramatic changes in the scattering curves. The scattering curve at the lowest ratio indicated an almost coil-like behaviour, while at the higher ratios the scattering curves supported the model of highly contracted polymer chains. Most of X-ray scattering experiments on intermediate states revealed compact structural elements which were significantly smaller than the respective overall size of the NaPA particles.
PACS.61.10.Eq X-ray scattering (including small-angle scattering) 82.35.Rs Polyelectrolytes 78.35.+c Brillouin and Rayleigh scattering; other light scattering
Unable to display preview. Download preview PDF.
- 2.P. Flory, Principles of Polymer Chemistry (Cornell University Press, Ithaca, 1953).Google Scholar
- 3.A. Takahashi, S. Yamori, I. Kagawa, Kogyo Kagaku Zasshi 83, 11 (1962).Google Scholar
- 40.S.W. Provencher, Comput. Phys. Commun. 27, 213Google Scholar
- 45.O. Glatter, O. Kratky (Editors), Small Angle X-ray Scattering (Academic Press, London, 1982).Google Scholar
- 46.W. Burchard, Adv. Polym. Sci. 48, 1 (1983).Google Scholar
- 50.C. Wu, S. Zhou, Macromolecules 28, 5388Google Scholar
- 51.W. Burchard, M. Schmidt, W.H. Stockmayer, Macromolecules 13, 580Google Scholar
- 52.W. Burchard, M. Frank, E. Michel, Ber. Bunsenges. Phys. Chem. 100, 807 (1996).Google Scholar
- 54.Lord Rayleigh, Proc. R. Soc. London, Ser. A 90, 219 (1914).Google Scholar