Regensburg 2025 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 32: Poster Session II

CPP 32.7: Poster

Thursday, March 20, 2025, 09:30–12:00, P3

Adaptive Air-Water Interfaces with Spiropyrans and Arylazopyrazoles — •Michael Hardt¹, Javier Carrascosa-Tejedor², Philipp Gutfreund², Richard A. Campbell³, and Björn Braunschweig¹ — ¹University of Münster (Germany) — ²Institut Laue-Langevin (France) — ³University of Manchester (UK)

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. Using molecular switches that respond to orthogonal triggers, the properties of fluid interfaces can be preconditioned, and a low level of adaptivity can be integrated, extending the possibilities of soft matter interfaces beyond responsive functions. We explore the adaptive behaviour of air-water interfaces decorated by spiropyran (SP) and arylazopyrazole (AAP) photo-responsive surfactants. When exposed to UV light, the SP surfactants become more surface active, while the AAP surfactants undergo E/Z photoisomerization, significantly reducing their surface activity. By adjusting the intensity and duration of the UV exposure, the interfacial properties can be shifted from a simple responsive state (upon weak UV irradiation) to a more complex conditioned response (upon intense UV irradiation), accompanied by a dramatic alteration in interfacial chemistry. Vibrational sum-frequency generation (SFG) and neutron reflectometry suggest that prolonged UV exposure induces SP and AAP surfactant aggregation at the air-water interface, driving the conditioned response where thick SP layers up to 5 nm form in the presence of Z-AAP.

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