Regensburg 2016 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 23: Charged Soft Matter

CPP 23.4: Vortrag

Dienstag, 8. März 2016, 15:00–15:15, H40

Ion Pairing and Charging at Nanodroplet Surfaces in Oil/Water Emulsions — •Björn Braunschweig¹, Christian Sauerbeck¹, Andreas Krause², Frank R. Beierlein², Timothy Clark², and Wolfgang Peukert¹ — ¹Institute of Particle Technology — ²Computer Chemistry Center, FAU Erlangen-Nürnberg

Molecular structures and interactions at oil/water interfaces are of great importance for emulsions and their properties such as stability or rheology. In our contribution, we demonstrate that not only the emulsifier coverage and structure, but also the solvation at the interface can significantly influence adsorption. Interfacial properties of emulsions were studied as function of sodium dodecyl sulfate (Na⁺DS⁻) and NaCl electrolyte concentrations. Experimental results from second-harmonic light scattering at the surface of nanodroplets with a mean radius of 83 nm were corroborated by extensive molecular dynamics (MD) simulations of hexadecane/water interfaces. We have experimentally determined the maximum surface excess of DS- anions (2.6 µmol/m²) and the Gibbs free energy of adsorption (ΔG) in the presence of Na⁺. Comparing 0 to 5 mM NaCl concentrations we show that ΔG changes from -34 to -41 kJ/mol. This change in ΔG is attributed to a formation of contact ion pairs (CIPs) between DS⁻ anions and Na⁺ cations, which have a higher propensity to adsorb at the hexadecane/water interfaces. MD simulations clearly show that CIPs are formed and thus strongly corroborate conclusions from our experiments. In fact, MD simulations provide a more complete picture of Na⁺, DS⁻ and water molecules at and near the interfacial region.