Berlin 2024 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 28: Poster III

CPP 28.47: Poster

Mittwoch, 20. März 2024, 11:30–13:30, Poster C

Light-Driven Charge Regulation at Oil/Water Interfaces in Nanoemulsions — •Dana Glikman and Björn Braunschweig — Institute of Physical Chemistry and Center for Soft Nanoscience, University of Münster, Busso-Peus-Str. 10, 48149 Münster

Understanding oil/water (o/w) interfaces in nanoemulsions and on a molecular level is of great interest, but often impaired by experimental limitations to probe the internal interfaces in situ. In order to study and to tune nanoemulsions we make use of photoswitchable surfactants. For that we apply arylazopyrazole sulfonate (butyl-AAP) surfactants which can be photoisomerized between E and Z isomers by visible and UV light. This causes massive changes in the interface tension at the extended o/w interface and a drastic shift in the surfactants’ CMC, which we apply to control the stability of the macroemulsions through UV irradiation. Nanoemulsions with a droplet radius of 90 nm were, however, not susceptible to E/Z photoisomerization in terms of changes in particle size or in the ζ-potential. However, second-harmonic generation in the scattering mode (SHS) shows that the surfactants’ surface excess at the nanoscopic o/w interface is changed drastically and reversibly by E/Z photoisomerization. The apparent differences in the ζ-potential and the changes in surface excess provide evidence for a fixed charge to particle size ratio and the need for counter ion condensation in order to renormalize the particle charge to a critical charge per particle, which is largely different to extended interfaces.

Keywords: Responsive interfaces; Nanoemulsions