Berlin 2015 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 52: Focus: Electrolytes at Interfaces - Stern Layer (joint session with CPP, BP)
CPP 52.7: Vortrag
Mittwoch, 18. März 2015, 17:15–17:30, C 130
Breaking the Symmetry of Ions at the Air-Water Interface — •Eva Brandes1, Peter Karageorgiev1, Padmanabhan Viswanath2, and Hubert Motschmann1 — 1Institute of Physical and Theoretical Chemistry, University of Regensburg, D-93040 Regensburg, Germany — 2Centre for Nano and Soft Matter Sciences, Jalahalli, Bangalore 560013, India
The air-water interface is a widely discussed system. Controversial opinions exist especially for the arrangement of dissolved ions close to the interface; while the classical picture predicts depletion, more recent investigations suggest a nonmonotonous concentration profile with an enrichment layer followed by a depletion layer. A sophisticated method to investigate the air-water interface is the IR-vis sum frequency generation (SFG) spectroscopy, because this method is intrinsically surface specific for soft media.
In this contribution we investigated the behavior of octahedral metal complex ions close to the air-water interface. No SFG signal is expected for octahedrons unless there is a reduction in symmetry. This distortion can only take place close to the interface because only there is a non-isotropic environment. We got SFG responses from the octahedrons, revealing that they are close to the interface. Furthermore we measured the surface excess via a surface tension isotherm, which turns out to be negative. The combined measurements suggest a nonmonotonous concentration profile.