Stretchable and Reactive Membranes of Metal???Organic Framework Nanosurfactants on Liquid Droplets Enable Dynamic Control of Self???Propulsion, Cargo Pick???Up, and Drop???Off

Sub???micrometer metal???organic framework (MOF) particles form sturdy yet dynamic???that is, structurally reconfigurable and chemically active???coatings at the interface between an aqueous droplet and the surrounding organic phase. Upon an external stimulus, the MOF particles change their interfacial orientation/packing, allowing the membranes to stretch, open, and close. At the same time, these MOF particles catalytically decompose hydrogen peroxide fuel to provide the gas???bubble recoil needed to propel the droplets; when the droplets are covered with only patches of the ZIF???67 MOFs, the recoil and self???propulsion are directional. A combination of all these effects underlies the construction of a chemical system in which the external objects are engulfed by the droplet opening up and closing its MOF membrane, are subject to chemical processing inside of the droplet, are transported to another location, and are ultimately expelled into the surrounding solvent, in effect realizing a primitive chemical mimic of phagocytosis