(120a) Stoppers and Skins on Clay Nanotubes Help Stabilize Oil-in-Water Emulsions and Modulate the Release of Encapsulated Surfactants

This work develops the concepts of particle stabilized emulsions by using nano-tubular natural clays known as halloysites to attach to the oil-water interface and stabilize oil-in-water emulsions. Such nanotubular halloysite nanotubes (HNT) serve as reservoirs for surfactants and are able to deliver surfactants to the oil-water interface and thus lower the oil-water interfacial tension. This two-step concept of surfactant delivery and droplet stabilization by particles has significant implications to oil spill remediation. However, to deliver surfactant loaded HNTs in a water based solvent slurry it is important to stopper the nanotubes to prevent premature release of the surfactant. This work focusses on the use of an environmentally benign two-dimensional metal organic framework formed by coordinating Fe (III) with a polyphenolic as a stoppering agent. Such molecularly thin networks form a skin around the HNTs thus providing a way to effectively sequester surfactant cargo for controlled release. Cryo-scanning electron microscopy (Cryo-SEM) shows that these HNTs and HNT bundles attach to the oil-water interface with side-on orientation. Inverted drop tensiometry was used to characterize the dynamic interfacial tension resulting from the release of a model surfactant (Tween 80) from the HNTs and indicates that the stoppers are effective in sequestering the surfactant cargo for extended periods at neutral pH values. Release triggered by framework disassembly at acidic pH values can be effected just prior to delivery to oil spills. The concepts and scalability of this process have significant implications for oil spill remediation, enhanced oil recovery, biomedical and pharmaceutical applications.