Supramolecular Microgel Disassembly to Control Pickering Emulsion Stabilization and Destabilization

Abstract Microgel-stabilized Pickering emulsions are of great interest both in fundamental science and in applications for their long-term stability and their possible on-demand destabilization by microgel stimulation. In previous studies, the microgel structure has been proven to be a key parameter in the emulsion stabilization mechanism. Here, we take advantage of the on-demand controlled degradation of PNIPAM-based supramolecular microgels to modify in situ their structure and thus study the role of this parameter in both the emulsion stabilization and destabilization mechanisms. First, the study of microgels with different architectures confirms that, at a given microgel concentration, microgels with a more pronounced core–shell structure and/or a smaller cross-linker content more efficiently limit droplet coalescence and thus lead to smaller surface coverage and smaller droplet sizes. This result is attributed to the lower cross-linker concentration in the microgel shell that can entangle more efficiently at the droplet interface. Second, the partial cleavage by chemical oxidation of the supramolecular cross-linkers, based on an Fe(II)/bis-terpyridine complex, allows us to modify in situ the shell cross-linker content before emulsification and thus to confirm its key role in the emulsion stabilization mechanism. Third, the control of the complete microgel degradation kinetics, directly linked to the initial supramolecular cross-linker distribution and content, permits to finely tune the emulsion destabilization time. Therefore, the use of a cleavable supramolecular cross-linker not only permits us to elucidate the complex mechanisms governing the stabilization and destabilization of microgel-stabilized emulsions but also opens possibilities for the development of responsive emulsion systems with well-controlled properties.