Hierarchical Oil–Water–Oil Pickering Double Emulsions Stabilized by Tubular Nanoparticles

Pickering emulsions stabilized by a small fraction of submicrometer-size clay tubes provide stable and tunable soft-matter systems with relevance across multiple fields. We here introduce a novel oil-in-water-in-oil Pickering double emulsion system stabilized by selectively functionalized halloysite nanotubes. The stability of the double emulsions was achieved through the combined use of pristine and surface-modified halloysite nanotubes, which selectively stabilized the oil-in-water and water-in-oil interfaces in the two separately prepared colloids. After these two samples were mixed and stirred, a hierarchical structure of oil microdroplets inside water droplets dispersed in bulk oil was obtained. Fluorescent microscopy and particle-tracking analyses confirmed that oil droplets confined within the double emulsion exhibit Brownian motion with decreased diffusion coefficients. The resulting dual-compartment structure enables the simultaneous encapsulation of hydrophilic and hydrophobic species, promising applications in controlled delivery and multifunctional formulations.