Authors
Odile Carrier
Ellen H G Backus
Noushine Shahidzadeh
Johannes Franz
Manfred Wagner
Yuki Nagata
Mischa Bonn
Daniel Bonn
Date (dd-mm-yyyy)
2016-03-03
Title
Oppositely Charged Ions at Water-Air and Water-Oil Interfaces
Subtitle
Contrasting the Molecular Picture with Thermodynamics
Journal
The Journal of Physical Chemistry Letters
Volume
7
Publication Year
2016-03-03
Pages
825-830
Issue number
5
Document type
Article
Faculty
Faculty of Science (FNWI)
Institute
Van der Waals-Zeeman Institute (WZI)
Institute for High Energy Physics (IHEF)
Institute of Physics (IoP)
Abstract

The surface-active ions tetraphenylarsonium (Ph4As+) and tetraphenylboron (Ph4B-) have a similar structure but opposite charge. At the solution-air interface, the two ions affect the surface tension in an identical manner, yet sum-frequency generation (SFG) spectra reveal an enhanced surface propensity for Ph4As+ compared with Ph4B-, in addition to opposite alignment of interfacial water molecules. At the water-oil interface, the interfacial tension is 7 mN/m lower for Ph4As+ than for Ph4B- salts, but this can be fully accounted for by the different bulk solubility of these ions in the hydrophobic phase, rather than inherently different surface activities. The different solubility can be accounted for by differences in electronic structure, as evidenced by quantum chemical calculations and NMR studies. Our results show that the surface propensity concluded from SFG spectroscopy does not necessarily correlate with interfacial adsorption concluded from thermodynamic measurements.

URL
go to publisher's site
Permalink
https://hdl.handle.net/11245.1/e657ba83-8c1c-47bc-a523-579e8d768196