Dumbbell-shaped 3-APF@SiO2 Janus particles constructed by oil-water interface growth for acidic/basic dual pH-responsive stabilizer of Pickering emulsions.

Dumbbell-shaped Janus particles with asymmetric morphology, completely separated hydrophilic and lipophilic regions, and acidic/basic dual pH-responsive functional groups (DHL-ABR JPs) are in high demand because they can endow Pickering emulsions with excellent stability and flexible switching ability between emulsification and demulsification by simply changing pH value of the system. Herein, we propose a novel "oil-water interface growth" strategy to directly access 3-aminophenol-co-formaldehyde@SiO2 (3-APF@SiO2) DHL-ABR JPs with average particle size of ∼250 nm and size distribution index of 0.012. The formation mechanism was systematically investigated. Interestingly, the particle morphology could be precisely tuned from dumbbell to hamburger, and then to popcorn by simply changing the dropping time of tetraethyl orthosilicate. Additionally, the snowman-shaped particles, consisting of SiO2 and poly (acrylic acid-co-butyl acrylate) at two ends respectively, were prepared via this method. Remarkably, the Pickering emulsion stabilized by 3-APF@SiO2 DHL-ABR JPs showed excellent emulsification effect, i.e. the oil droplet diameter and emulsification index of the Pickering emulsion remained almost unchanged even after storage for one year and sensitive dual pH-response characteristics, i.e., emulsified at pH = 7, and demulsified at pH = 4 and 10. It is believed that this work paves a new avenue for synthesis and application of various asymmetric nanoparticles.