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Märstetten-Dorf, Switzerland

Scheu R.,Institute of Bio Engineering IBI | Chen Y.,Institute of Bio Engineering IBI | De Aguiar H.B.,Institute of Bio Engineering IBI | Rankin B.M.,Purdue University | And 2 more authors.
Journal of the American Chemical Society | Year: 2014

Specific ion effects can influence many processes in aqueous solutions: protein folding, enzyme activity, self-assembly, and interface stabilization. Ionic amphiphiles are known to stabilize the oil/water interface, presumably by dipping their hydrophobic tails into the oil phase while sticking their hydrophilic head groups in water. However, we find that anionic and cationic amphiphiles adopt strikingly different structures at liquid hydrophobic/water interfaces, linked to the different specific interactions between water and the amphiphile head groups, both at the interface and in the bulk. Vibrational sum frequency scattering measurements show that dodecylsulfate (DS-) ions do not detectably perturb the oil phase while dodecyltrimethylammonium (DTA+) ions do. Raman solvation shell spectroscopy and second harmonic scattering (SHS) show that the respective hydration-shells and the interfacial water structure are also very different. Our work suggests that specific interactions with water play a key role in driving the anionic head group toward the water phase and the cationic head group toward the oil phase, thus also implying a quite different surface stabilization mechanism. © 2014 American Chemical Society.

De Aguiar H.B.,Institute of Bio Engineering IBI | De Aguiar H.B.,Max Planck Institute for Intelligent Systems (Stuttgart) | Scheu R.,Institute of Bio Engineering IBI | Scheu R.,Max Planck Institute for Intelligent Systems (Stuttgart) | And 5 more authors.
Physical Chemistry Chemical Physics | Year: 2012

We present a comparison between sum frequency scattering (SFS) and reflection mode sum frequency generation (R-SFG). We have used scattering theory to describe both scattering experiments as well as reflection mode experiments. The interfacial vibrational spectrum of nanoscopic oil droplets dispersed in water was probed with SFS as well as with R-SFG. Spectra recorded in phase-matched R-SFG mode and spectra recorded with SFS from the same sample are different, which shows that different interfaces are measured. Scattering spectra at different scattering angles agree with nonlinear light scattering theory. We further present experiments with polymer films aimed at quantifying the comparative strength of R-SFG and SFS experiments. © 2012 the Owner Societies.

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