Berlin 2018 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 14: Interfaces and Thin Films I

CPP 14.6: Vortrag

Montag, 12. März 2018, 16:15–16:30, C 264

Specific Ion Effects of Nd³⁺ on the Structure and the Charging State of β-Lactoglobulin Adsorption Layers — Manuela Richert and •Björn Braunschweig — Institute of Physical Chemistry, Westfälische Wilhelms-Universität Münster, Corrensstraße 28/30, 48149 Münster, Germany

The influence of Nd³⁺ cations on β-Lactoglobulin (BLG) at air/water interfaces was investigated as a function of NdCl₃ concentration at a constant protein concentration of 15 µM. In addition, we studied the proteins’ bulk charging state with ζ-potential measurements and observe a complete reversal of the ζ-potential from -40 to +25 mV at low and high c(NdCl₃), respectively. The zero net charging in the bulk is observed between 25 and 50 µM NdCl₃, which is linked to a low colloidal stability. At the air/water interface, vibrational sum-frequency generation (SFG) shows a minimum in intensity of O-H stretching bands and a 180^∘ phase change of the latter bands. We attribute these observations to a change in the net orientation of interfacial water molecules. The extreme charge screening of Nd³⁺ ions leads to a reduction of electrostatic repulsive forces and thus to a higher surface excess of BLG. As a result, the equilibrium surface tension decreases from 57 to 50 mN/m when the NdCl₃ concentration is increased to 200 µM. Foams show substantial changes in mean bubble size, stability and foamability as a function of NdCl₃ concentration. We relate these observations to changes in electrostatic disjoining pressure at low and intermediate c(NdCl₃) until interfacial BLG aggregates lead to non-DLVO stabilization of the foams.