Polystyrene‐Silica Colloidal Janus Particles with Uniform Shapes and Complex Structures

Abstract Colloidal Janus particles with well‐controlled parameters are sought for a range of applications in mesoscale self‐assembly, stabilization of Pickering emulsion, and development of multifunctional devices, among others. Herein, a versatile method for fabricating polystyrene‐silica (PS‐SiO 2 ) Janus particles featuring complex shapes and structures is developed by swelling PS@SiO 2 core–shell spheroids. When the PS encapsulated in a rigid SiO 2 shell is swollen by a good solvent for PS, the swelling‐induced pressure will result in an uneven distribution of stress acting on the SiO 2 shell, as determined by the intrinsic symmetry of a spheroid. When the stress reaches a threshold value, the swollen PS will preferentially poke out from equatorial sites on the SiO 2 shell to form T‐shaped Janus particles comprised of PS and SiO 2 compartments. The size of the PS portion can be controlled by varying the extent of swelling, while the size, shape, and shell thickness of the SiO 2 portion are determined by the original PS spheroids and the SiO 2 coating. This solution‐phase method holds promise to produce Janus particles with diverse shapes, structures, and compositions for various applications. The T‐shaped Janus particles can serve as an emulsifier to effectively stabilize an oil‐in‐water (O/W) Pickering emulsion for at least 35 days.