Dresden 2017 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 15: Solid-Liquid Interfaces: Structure, Spectroscopy II

O 15.2: Vortrag

Montag, 20. März 2017, 15:15–15:30, WIL B321

Unraveling water structuring on Nafion-like sulfonate-based model surfaces with increasingly hydrophobic character using force spectroscopy — •Laila Moreno Ostertag1, Xiao Ling2, Thomas Utzig1, Philipp Stock1, Sapun Parekh2, Katrin Domke2, and Markus Valtiner1,31Max-Planck-Institut für Eisenforschung, Max-Planck-Str. 1, 40237 Düsseldorf - Germany — 2Max-Planck-Institut für Polymerforschung, Ackermannweg 10, 55128 Mainz - Germany — 3Institut für Physikalische Chemie der TU Bergakademie Freiberg, 09599 Freiberg - Germany

Nafion membranes are an essential component of fuel cells, providing an effective medium to separate cathode and anode while facilitating proton conduction. Specifically, Nafion is a porous material with 1-2 nm pore diameters. The way water is structured across a pore is essential to understand the mechanism of proton transport. Here, we used atomic force microscopy to measure interaction forces between Nafion-like model surfaces emulated via self-assembled monolayers (SAM) where SO3- groups were gradually substituted by hydrophobic groups. The resulting interaction force profiles can be fitted to extended DLVO models depending on hydrophobic or charged content, in order to gain insight into the molecular surface structure that gives rise to the measured forces. Our data indicates a non-linear trend of the solvent structure at the surface as a function of the hydrophobic-to-sulfonate group ratio, indicating that small changes in stoichiometry can significantly alter water layering. We will discuss how our results relate to proton conductivity and how they may help to optimize membrane properties.

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