Berlin 2024 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 4: Interfaces and Thin Films

CPP 4.11: Talk

Monday, March 18, 2024, 12:15–12:30, H 0111

Adaptive Air-Water Interfaces with Spiropyran and Aryl-
azopyrazole Photoswitches — •Michael Hardt and Björn Braunschweig — University of Münster, Center for Soft Nanoscience, 48149 Münster, Germany

Interfaces that can be tuned in their properties by external stimuli such as light or temperature are of great interest to drive macroscopic properties of interface-controlled soft matter materials and offer the possibility to integrate adaptive functions. Using molecular switches that respond to orthogonal triggers, the properties of fluid interfaces can be preconditioned, resulting in a low level of adaptivity that extends the possibilities of soft matter interfaces beyond being purely responsive. In this contribution, we report on air-water interfaces decorated by spiropyran (SP) and arylazopyrazole (AAP) photo-responsive surfactants. The SP surfactants increase their surface activity when irradiated with UV light, which causes a ring-closure reaction. E/Z photo-isomerization of the AAP surfactants causes a substantial decrease in surface activity and, thus, desorption from the interface. At low pH, the short thermal lifetimes of the surfactant isomers offer the use of a thermal dissipative pathway as an alternative trigger to regain the initial properties. The combination of SP and AAP surfactants allows to precondition the interface with UV light and to gain adaptive interfacial properties. This is characterized by surface tensiometry and vibrational sum-frequency generation (SFG) that provide information on interfacial composition as well as on interfacial kinetics.

Keywords: responsive; adaptive; air-water interface; sum-frequency generation; tensiometry