Sugar-responsive Pickering emulsions mediated by switching hydrophobicity in microgels

International audienceHypothesis: Pickering emulsions stabilized by soft and responsive microgels can demulsify on demandupon microgel collapse. The concept has been explored with simple model microgels such as poly(Nisopropylacrylamide)(pNIPAM) and their derivatives, but the role of functionalization is largely unexplored.Experiments: Saccharide-responsive phenylboronic-modified microgels are used as Pickering emulsionstabilizers. Emulsion stability and microgel organization at drop surface are studied as a function of saccharideconcentration. Better insight into their behavior at interfaces is gained through adsorption kineticsand Langmuir film studies at air-water interface.Findings: The functionalization of water-swollen microgels by phenylboronic functions imparts somehydrophobicity to the structure, at the origin of additional internal cross-links analogous which rigidifythe structure compared to non-functionalized microgels, as proved by their slow adsorption kinetics andpoor interfacial compressibility. Upon boronate ester formation with diol groups of the saccharide, thehydrophobic character of the phenylboronic acid decreases, increasing the adsorption kinetics and theirinterfacial compressibility. Emulsions are stable in the presence of saccharide, given the high deformabilityof the yet-hydrophilic microgels, and mechanically unstable with less deformable particles in lo