Berlin 2018 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 20: Poster Session I

CPP 20.61: Poster

Monday, March 12, 2018, 17:30–19:30, Poster A

Quantifying surface potentials at liquid-gas interfaces from vibrational SFG spectroscopy — Eric Weißenborn, Felix Schulze-Zachau, Georgi Gochev, •Natalia García Rey, and Björn Braunschweig — Institute of Physical Chemistry, Westfälische Wilhelms-Universität Münster, Corrensstrasse 28/30, 48149 Münster, Germany

Knowing the double layer potential (ψ₀) of the liquid-gas surface is essential to analyze the mechanisms of foam stabilization. However, no straightforward method is available to measure ψ₀. The intrinsic negative charging of pure water surface is significantly modified by adsorbing ionic surfactants while non-ionic surfactants change only slightly the ψ₀-magnitude. Adsorption of cationic surfactants will first neutralize the surface negative charge and further will cause charge reversal. By mixing non-ionic and cationic surfactants, we can tune the negative/zero/positive ψ₀ at the air-water surface. On charged interfaces, the SFG intensity depends not only on the 2^nd-order of susceptibility (χ⁽²⁾) but also on the 3^rd-order (χ⁽³⁾) due to impact of ψ₀. SFG spectroscopy used to quantifying the ψ₀ requires first its calibration to untangle the χ⁽²⁾ and χ⁽³⁾ from the spectra. ψ₀ is estimated from theoretical (DLVO) analysis of the disjoining pressure isotherm for a foam film as measured with the thin-film pressure balance (TFPB) technique. These experiments will allow for validation of data form OH-SFG spectra taken for isolated surface that can be applied to extract ψ₀-values. This is the first study to our knowledge that combines TFPB and SFG experiments for studying soft interfaces.