Hansch, M.

2017
UB-PAD - Paderborn University Library Paderborn

Abstract: Interactions between polyelectrolytes (PE) and specifically interacting cations (SIC) in dilute aqueous solutions were investigated in the present work by various scattering methods and isothermal titration calorimetry. The focus lies on the combination of Al3+-polystyrene sulfonate (AlPSS) and Ba2+-polystyrene sulfonate (BaPSS).It could be shown that the phase diagram of polystyrenesulfonate in the presence of Al3+ exhibits a phase boundary, which shows a linear correlation between the amount of salt necessary to precipitate the polyelectrolyte and the molar concentration of the negative residues of the polyelectrolyte. Below the threshold the AlPSS samples are stable, while precipitation of the AlPSS chains can be observed at states located beyond the threshold. The phase diagram of polystyrenesulfonate in the presence of Ba2+ exhibits also a stable regime at low barium and an instable regime at higher Ba2+ concentrations. Both regimes are separated from each other by an unusual horizontal threshold. In both combinations a shrinking of the PSS chains can be observed with an increasing concentration of Al3+ or Ba2+. The structure of AlPSS stays coil-like even at points close to the phase boundary, while the BaPSS chains become more compact, but without collapsing to a compact sphere. An implementation or an increase of an inert salt concentration, leads to a shift of the threshold to higher SIC concentrations. ITC measurements on various SIC-PE combinations underlines that the binding of the SICs to the PE is in nearly all cases, which were investigated, an entropically driven process. Just in case of BaPSS it can be concluded that the binding process is exothermic.The present results on AlPSS and BaPSS make available a detailed comparison with corresponding studies performed with complexes of SIC-polyacrylates.

Keyword(s): Chemical Reactions and Advanced Materials (1st) ; Chemistry (2nd)

1. EDV
2. JCNS-FRM-II (JCNS (München) ; Jülich Centre for Neutron Science JCNS (München) ; JCNS-FRM-II)

1. KWS-3: Very small angle scattering diffractometer with focusing mirror (NL3auS)