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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 88: Responsive and Adaptive Systems

CPP 88.3: Vortrag

Donnerstag, 19. März 2020, 10:00–10:15, ZEU 114

Photo-switchable surfactants for responsive air-water interfaces: Azo vs AAP amphiphiles — •Marco Schnurbus¹, Richard Campbell², Jörn Droste¹, Christian Honnigfort¹, Philipp Gutfreund³, Michael Hansen¹, and Björn Braunschweig¹ — ¹Institute of Physical Chemistry, WWU Münster — ²Division of Pharmacy & Optometry, Manchester — ³ILL, Grenoble

Two photo-switchable ammonium bromide surfactants (Azo-TB and AAP-TB) were compared with respect to their switching ability. Both surfactants were studied with UV/Vis and NMR spectroscopy in the bulk and with sum-frequency generation (SFG), neutron reflectometry (NR) and tensiometry at the air-water interface. The surfactants undergo photo-isomerization reactions from their Z and E conformation when irradiated with 365 nm UV and 520 nm green light. NMR spectroscopy showed a higher photostationary state (PSS) for the E-isomer under green light irradiation for the AAP-TB, whereas the Z-isomer under UV light had a higher PSS for the Azo-TB. Tensiometry demonstrates the surfactants ability to reversibly change the surface tension with light irradiation, which yields a maximum change in surface tension of 12 mN/m and 8 mN/m for AAP-TB and Azo-TB surfactants, respectively. Furthermore, the surface excess from NR as well as the aromatic C-H band and the nonresonant contribution to the SFG spectra demonstrate higher switching abilities for the AAP-TB surfactant. In addition, analysis of SFG spectra from O-H and C-H stretching bands of Azo-TB and AAP-TB surfactants indicate surfactant desorption from the air-water interface when irradiated with UV light.