Reversible demulsification and emulsification of surfactant emulsions regulated by light-responsive azo functionalized copper nanoclusters

An emulsion system with reversible demulsification/emulsification transition triggered by light irradiation was achieved by azo-modified copper nanoclusters Cu 3 (azopz) 3 ( Cu3 , Hazopz = (3,5-dimethyl-4-(phenyldiazole)-1H-pyrazole)) in the surfactant (APG0810) oil-in-water emulsion. The phase separation behavior of the emulsion is attributed to the fibrous structures self-assembled from Cu3 in the toluene phase under 365 nm UV irradiation, which break the stability of the emulsion, resulting in the demulsification. Further visible light irradiation and homogenization could recover the emulsion. This process is completely reversible under alternating ultraviolet/visible light treatments. This study shows the first application of metal nanoclusters in controlling demulsification/emulsification by a noninvasive stimulus. Further development of sustainable chemical processes such as catalyst recycling, product separation and hydrogenation reaction is highly expected based on this research.