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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 50: Poster Session III

CPP 50.43: Poster

Dienstag, 17. März 2020, 14:00–16:00, P1C

Spiropyran Sulfonates for Photo and pH Responsive Air-Water Interfaces and Aqueous Foam — •Marco Schnurbus¹, Malgorzata Kabat², Ewelina Jarek², Marcel Krzan², Piotr Warszynski², and Björn Braunschweig¹ — ¹Institute of Physical Chemistry, WWU Münster — ²IKiFP PAN, Krakow

The photochromic reaction of a spiropyran sulfonate surfactant was used to render interfacial and foaming properties active to light stimuli. We have applied sum-frequency generation (SFG) spectroscopy which has provided information on the surface excess and the interfacial charging state as a function of light irradiation and solution pH. Under blue light irradiation, the surfactant forms a closed ring, spiro form (SP), whereas under dark conditions the ring opens and the merocyanine (MC) form is generated. The MC surfactants O-H group can be deprotonated as a function of pH, which is used to tune the molecules net charge at the interface. SFG spectroscopy shows that with increasing pH the intensity of O-H stretching band from interfacial water molecules increases, which we associate to an increase in surface net charge. At a pH of 5.3, irradiation with blue light leads to a reversible decrease of O-H intensities, whereas the C-H intensities were unchanged compared to the corresponding intensities under dark conditions. Measurements of the foam stabilities showed a higher foam stability under dark light conditions. At pH 2.7 this behavior is reversed as far as the surface tension and charging as well as the foam stability are concerned. The light-triggered changes at both pH values can be used to control foams and interfaces on a molecular level.