Bioinspired polydopamine coating as a versatile platform for synthesizing asymmetric Janus particles at an air-water interface

Janus particles with controlled asymmetries and functionalities represent promising building blocks and functional materials due to their unique anisotropic features. Herein, we show a facile and general approach towards preparing colloidal Janus particles with adjustable surface asymmetries and functionalities based on monolayer colloidal crystal (MCC) templates combined with mussel-inspired polydopamine (PDA) chemistry at an air-water interface. First, monodisperse colloidal polystyrene/polydopamine (PS/PDA) Janus particles with tunable asymmetrical geometries are synthesized by polymerizing dopamine onto two-dimensional (2D) polystyrene (PS) monolayer colloidal crystals formed at the air-water interface. Moreover, the good chemical reactivity of the PDA coating makes it a versatile platform to introduce a variety of functional materials, e.g., metal nanoparticles and organic molecules, producing colloidal Janus particles with adjustable functionalities. Finally, we demonstrate this synthetic strategy not only provides a controllable method for the fabrication of monodisperse colloidal Janus particles but also opens up a new Janus platform for artificially designed Janus particles with tunable asymmetries and functionalities.