(732b) Forced Nanoparticle Desorption From Oil-Water Interfaces: a Route to Particle Recovery and Recycling

Nanoparticle-stabilized emulsions are exploited in energy-related applications such as phase-transfer catalysis and mobility control in enhanced oil recovery. These applications rely on a significant energy barrier that precludes spontaneous desorption of nanoparticles from the fluid interface during the processes that exploit them. On the other hand, this interfacial trapping poses significant challenges to nanoparticle recovery and recycling. In this work, we explore mechanically forced desorption of nanoparticles from oil-water interfaces as a route to nanoparticle recovery.

We study gold nanoparticles capped with an uncharged amphiphilic ligand, which spontaneously adsorb from an aqueous solution onto a pendant oil drop. Using pendant drop tensiometry, we measure the evolution of the surface pressure of the nanoparticle monolayer during adsorption and upon subsequent compression. Concomitantly, we use absorbance measurements to monitor in real time the surface coverage of the monolayer. This quantity is typically not directly measurable in systems where nanoparticles spontaneously adsorb to an interface from solution. From these data, we construct pressure-surface concentration isotherms, which display signatures of ligand-mediated repulsive interactions.

Upon strong compression beyond maximum coverage, the nanoparticles are forced out of the interface; ligand-mediated repulsion prevents aggregation and allows the particles to desorb and re-disperse in solution. This opens avenues to engineering nanoparticles to promote desorption under strong compression as opposed to monolayer buckling.