Berlin 2018 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 11: Responsive and Adaptive Systems
CPP 11.3: Vortrag
Montag, 12. März 2018, 11:45–12:00, C 230
Smart Air/Water Interfaces with Arylazopyrazol Surfactants and their Role in Responsive Aqueous Foam — •Marco Schnurbus1, Lucas Stricker2, Bart Jan Ravoo2, and Björn Braunschweig1 — 1Institute of Physical Chemistry — 2Organic Chemistry Institute, WWU Münster, 48149 Münster, Germany
A new light-switchable azo-surfactant arylazopyrazol tetraethylen glycol carboxylic acid (AAP-E4) was used as a building block to functionalize macroscopic foams. AAP-E4 was studied in the bulk with UV/Vis spectroscopy and at the interface with sum frequency generation as well as tensiometry. Foaming experiments were done with a dynamic foam analyzer in order to study the role of AAP-E4 surfactants within macroscopic foam. In the bulk, it is possible to switch the AAP-E4 surfactant reversibly from trans to cis configurations and vice versa using 380 nm UV and 520 nm green light. At the interface, we demonstrate excellent switching ability of AAP-E4 surfactants. We show that the responsiveness of the interface is strongly influenced by lateral electrostatic interactions. Consequently, the disjoining pressure and thus the foam stability are highly dependent on the bulk pH and the charging state of the interface. For that reason, we have studied both the surface net charge and the surface excess as important parameters that determine foam stability in this system and show that neutral pH conditions lead to the best compromise between switching ability, surface excess and surface charging. Measurements on the foam stability demonstrated that foams under illumination with green light are more stable compared to foams illuminated with UV light.