Mask-less preparation of Janus particles through ultraviolet irradiation on hydrophobic particles assembled at the air-water interface

Abstract

Janus particles are a class of materials that exhibit two contrasting properties. They possess unique properties, such as the ability to self-assemble at dissimilar liquid interfaces. Achieving high production yields remains a challenge to the practical application of Janus particles, as existing methods are generally tedious in the preparation procedures. The aim of this work is to prepare Janus particles using a process that is simple to facilitate scaling up. Semiconductor titanium dioxide (TiO2) and cuprous oxide (Cu2O) particles, pre-functionalized with hydrophobic coatings, were assembled at an air-water interface. The particles were then subjected to ultraviolet irradiation, which degraded the hydrophobic coating on the exposed side, and subsequently recovered through the removal of water. Janus particles that contained contrasting wettability over their surfaces were successfully obtained; the particle surfaces were demonstrated to be partially functionalized through comparison in the self-assembly behavior with fully-functionalized and non-functionalized particles. The obtained TiO2 Janus particles have demonstrated a Janus balance factor close to 1, and remained attached to the oil/water interface with long-term stability. The presence of a photocatalytic substrate was found to be necessary to accelerate the degradation of the coating. Different alkylsilane coatings, particle types, and irradiation durations were examined, leading to different types of Janus particles. The method can be potentially extended to other semiconductor metal oxide particles to generate Janus-like properties.