Dresden 2017 – scientific programme
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 47: Fluids and Interfaces I
CPP 47.4: Talk
Wednesday, March 22, 2017, 17:15–17:30, ZEU 255
Influence of Surfactant Chain Length on the Interfacial Structure and Properties of Surfactant/Polyelectrolyte Mixtures — •Felix Schulze-Zachau and Björn Braunschweig — Institut für Physikalische Chemie, Westfälische Wilhelms-Universität Münster, D-48149 Münster, Germany
Mixtures of poly(sodium 4-styrenesulfonate) (NaPSS) polyelectrolytes and 0.1 mM alkyltrimethylammonium bromides C16TAB, C14TAB and C12TAB surfactants were studied at the air/water interface with tensiometry, ellipsometry and vibrational SFG spectroscopy as a function of PSS concentration. In addition, macroscopic foams from these mixtures were studied in order to relate the interfacial molecular structure and its charging state to foam stability. ζ-potential and turbidity measurements were done to investigate charge and equilibrium states of the respective systems in the bulk solution. The chemical potential of the surfactants to bind to PSS increases with their chain length, which results in different interfacial structures. For C16TAB, charge neutralization in the bulk and at the interface is observed close to equimolar concentrations and leads to bulk solutions that are far outside the thermodynamic equilibrium. Here, hydrophobic complexes aggregate and precipitate for C16TAB while binding to PSS is much weaker for C14TAB and C12TAB where no precipitation is observed. In case of C16TAB/PSS mixtures, SFG spectra indicate a phase shift of the water molecules that is indicative for a charge reversal at the interface at 0.09 mM. Complementary methods indicate a depletion of complexes from the interface when this point of zero charge is crossed.