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Abstract The dissolution of a polymeric solid typically starts with the absorption of solvent molecules, followed by swelling and volume expansion. Only when the extent of swelling reaches a threshold can the polymer chains be disentangled and then dissolved into the solvent. When the polymeric solid is encapsulated in a rigid shell, the swelling process will be impeded. Despite the widespread use of this process, it is rarely discussed in the literature how the polymeric solid is dissolved from the core for the generation of colloidal hollow particles. Recent studies have started to shed light on the mechanistic details involved in the formation of hollow particles through a template‐directed process. Depending on the nature of the material used for the template, the removal of the template may involve different mechanisms and pathways, leading to the formation of distinct products. Here, a number of examples are used to illustrate this important phenomenon that is largely neglected in the literature. This article also discusses how the swelling of a polymeric template encapsulated in a rigid shell can be leveraged to fabricate new types of functional colloidal particles. 

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‐SiO₂) Janus particles featuring complex shapes and structures is developed by swelling PS@SiO₂core–shell spheroids. When the PS encapsulated in a rigid SiO₂shell is swollen by a good solvent for PS, the swelling‐induced pressure will result in an uneven distribution of stress acting on the SiO₂shell, 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 SiO₂shell to form T‐shaped Janus particles comprised of PS and SiO₂compartments. The size of the PS portion can be controlled by varying the extent of swelling, while the size, shape, and shell thickness of the SiO₂portion are determined by the original PS spheroids and the SiO₂coating. 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.