Temperature-Responsive Janus Particles as Microsurfactants for On-Demand Coalescence of Emulsions.

A new strategy that utilizes temperature-responsive wax-based Janus particles as microsurfactants to simultaneously achieve enhanced emulsion stability, as well as, on-demand coalescence of emulsion droplets is presented. The dumbbell structure with different surface wetting properties on each side of the Janus particle enables the particles to strongly adsorb at the liquid-liquid interface, leading to excellent stability against coalescence for both water-in-oil (W/O) and oil-in-water (O/W) emulsions. Moreover, these Janus microparticles are composed of a hydrophilic acrylate resin and a hydrophobic wax compartment which transitions from a frozen to an oil-soluble molten state above the melting point. This allows the particle-adsorbed droplets to coalesce above a designated temperature, depending on the type of wax material used. It is envisioned that the excellent emulsion stability and the tunable and rapid response to local temperature enabled by the wax-based Janus particle offers new and exciting opportunities in the advancing technologies including micro-reactors and drug delivery systems to name a few.

Biocompatible amphiphilic Janus nanoparticles with enhanced interfacial properties for colloidal surfactants.

Emulsions in which water droplets are dispersed in fluorocarbon oil phase (W/F emulsions) serve as effective means to encapsulate bioactives and precisely execute reactions in confined space due to the gas permeability, chemical inertness, and biocompatibility offered by the continuous phase. While molecular surfactants consisting of perfluorinated polyether (PFPE) and polyethylene glycol (PEG) have been used to stabilize these emulsions, these surfactants cannot effectively prevent coalescence and cross-contamination between the neighboring droplets. Herein, we present Janus nanoparticles (F-SiO2-PEG) as biocompatible colloidal surfactants to achieve excellent stability in W/F emulsions. By utilizing monolayered wax colloidosomes as templates, we show that Janus silica nanoparticles with two distinctive surface wetting properties can be synthesized in high purity. Moreover, we demonstrate that additional PEGylation of these Janus particles allows these colloidal surfactants to strongly adhere at the W/F interface, granting excellent emulsion stability compared to the equivalent randomly functionalized nanoparticles and prevent non-specific adsorption of proteins. As the strategy outlined in this work is general, we anticipate that it can be further extended to prepare Janus particles with tailored interfacial properties for biomedical, cosmetics, and pharmaceutical applications involving emulsions.

Biocompatible Wax-Based Microcapsules with Hermetic Sealing for Thermally Triggered Release of Actives.

We present a microfluidic approach that utilizes temperature-responsive and biocompatible palm oil as the shell material in microcapsules to simultaneously achieve hermetic sealing as well as on-demand temperature-triggered release of the encapsulated actives. Unlike common paraffin waxes (e.g., eicosane), microcapsule shells comprising palm oil do not form pores or cracks during freezing and provide a hermetic seal, a nearly perfect seal that separates the core containing the actives from the surrounding environment over a prolonged period of time. This allows effective isolation and protection of complex cargoes such as small molecules with high diffusivity, strong acids, and cosmetic actives including niacinamide. Moreover, the palm oil shell melts above the defined melting temperature, allowing the on-demand release of the encapsulated actives. Furthermore, palm oil is biocompatible, is edible, and leaves a minimal footprint when used in personal care and cosmetic products, offering new perspectives in the design of microcapsules for cosmetic applications.