Responsive Material and Interfacial Properties through Remote Control of Polyelectrolyte-Surfactant Mixtures

Polyelectrolyte/surfactant (P/S) mixtures find many applications but are static in nature and cannot be reversibly reconfigured through the application of external stimuli. Using a new type of photoswitchable surfactants, we use light to trigger property changes in mixtures of an anionic polyelectrolyte with a cationic photoswitch such as electrophoretic mobilities, particle size, as well as their interfacial structure and their ability to stabilize aqueous foam. For that, we show that prevailing hydrophobic intermolecular interactions can be remotely controlled between poly(sodium styrene sulfonate) (PSS) and arylazopyrazole tetraethylammonium bromide (AAP-TB). Shifting the chemical potential for P/S binding with E/Z photoisomerization of the surfactants can reversibly disintegrate even large aggregates (>4 μm) and is accompanied by a substantial change in the net charging state of PSS/AAP-TB complexes, e.g., from negative to positive excess charges upon light irradiation. In addition to the drastic changes in the bulk solution, also at air-water interfaces, the interfacial stoichiometry and structure change drastically on the molecular level with E/Z photoisomerization, which can also drive the stability of aqueous foam on a macroscopic level.