Janus Nanoparticles with Tunable Amphiphilicity for Stabilizing Pickering-Emulsion Droplets via Assembly Behavior at Oil–Water Interfaces

Janus particles (JNPs) with controlled anisotropies are regarded as promising materials for sophisticated building blocks and assembly. Herein a straightforward method was proposed for the synthesis of uniformly distributed JNPs with controllable anisotropies, showing two compartmental bulbs with different surface wettability. The synthetic strategy is based on the phase separation-induced styrene liquid protrusion on seed poly(styrene-co-acrylic acid) (CPSAA) nanoparticles via controlled swelling, with the formed polystyrene (PS) and CPSAA compartments corresponding to the amount of monomers. The size (lateral length) ratio of formed PS and CPSAA bulbs, D_PS/D_CPSAA, defined as "Janusity", has been precisely tuned in the range of 0-0.91 by controlling the mass ratio of two monomers. Obtained JNPs with tunable amphiphilicity are utilized as colloid surfactants to prepare Pickering-emulsions of both water-in-oil (W/O) and oil-in-water (O/W) with proper Janusity. The stability of achieved W/O and O/W Pickering-emulsions is dependent on the adhesion energy of a JNP at the water-oil interfaces. Prepared JNPs have also being utilized to prepare and stabilize monodisperse droplets in microfluidic devices, demonstrating their high potential for fundamental research and practical applications.