Berlin 2018 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 62: Charged Soft Matter, Polyelectrolytes and Ionic Liquids III

CPP 62.12: Vortrag

Donnerstag, 15. März 2018, 12:30–12:45, C 243

Interfacial Water Structure and Properties of Non-Equilibrium CTAB/Polyelectrolyte Mixtures with different Molecular Weights — •Felix Schulze-Zachau and Björn Braunschweig — Institute of Physical Chemistry, Westfälische Wilhelms-Universität Münster, 48149 Münster, Germany

Mixtures of CTAB and 0.1 mM poly(sodium 4-styrenesulfonate) (NaPSS) with different molecular weights (MWs) from 10 kDa to 1 MDa were studied in the bulk with turbidity and ζ-potential measurements, while vibrational SFG spectroscopy and tensiometry provided information on the molecular structure of air/water interfaces. We also relate the molecular structure and the charging state of the interface to the stability and the structure of macroscopic foam. We propose that mostly negatively charged and well-solvated complexes are formed in the bulk at CTAB concentrations below 75 µM. This is corroborated by the negligible turbidity and the ζ-potential of the mixtures. Increasing the CTAB concentration to stoichiometric bulk mixing ratio yields complexes with negligible net charges. These complexes tend to aggregate and adsorb at the interface. The turbidity maximum is indicative to bulk aggregation and shifts with increasing MW to higher CTAB concentrations. The non-equilibrium nature of these mixtures is obvious from the surface tension kinetics which show two adsorption processes of free CTAB and aggregates. Above a threshold concentration, interfaces are dominated by free CTAB while positively charged complexes are well solvated in the bulk. This yields wet foams and is confirmed by measurements with deuterated CTAB.