Preparation of Janus Titanium Dioxide Particles via Ultraviolet Irradiation of Pickering Emulsions

Pickering emulsions are stabilized by solid particles assembled at an immiscible liquid-liquid interface. In this work, the use of such emulsions to prepare semiconductor Janus particles through UV-irradiation is explored. Titanium dioxide particles that are prefunctionalized with an alkylsilane or a fluoroalkylsilane are employed to obtain wax-in-water emulsion droplets, which consist of the particles partially embedded in the wax core. Different emulsion formation mechanisms are discussed. The emulsified wax droplets are then subjected to ultraviolet irradiation, which photocatalytically degrades the silanes on the exposed portion of the particle surfaces, leading to Janus particles containing partial silane coatings. The particles are finally recovered through dissolution of wax. The Janus particles, which have contrasting wettabilities over their surface, are characterized based on self-assembly behavior and bulk wetting performance in a compact film, as compared with nonfunctionalized and fully-functionalized homogeneous particles. Three different types of Janus particles are created and their characters are explained using the concept of the Janus balance. The method has the potential to produce large scale yields in a relatively short time, and can be potentially applied to other semiconductor particles for the generation of Janus particles.