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Dresden 2020 – scientific programme

The DPG Spring Meeting in Dresden had to be cancelled! Read more ...

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 50: Poster Session III

CPP 50.43: Poster

Tuesday, March 17, 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 Braunschweig11Institute 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.

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