Anisotropic Janus Particles with Variable Morphology via Controllable Polymerization-Induced Phase Separation of Core–Shell Structure

Janus particle enables multifunctional integration through distinct partitioning of different compositions and functions. However, the precise modulation of its morphology remains a challenge. Here, a phase separation-induced strategy was demonstrated to fabricate Janus particles with variable morphologies. Taking different monomers to swell the polymeric core of the core–shell structural polystyrene@silica (PS@SiO2) seeds, isotropic and anisotropic cores were achieved with different compatibility between the seed polymer and the as-formed one. When styrene/divinylbenzene (St/DVB) was employed to swell the core–shell seeds, the isotropic PS/poly(divinylbenzene) (PDVB) core formed in the polymerization process. Then, pistachio-shaped Janus particles were achieved after the swollen core broke the shell into two halves. Interestingly, when methyl methacrylate (MMA) was used, the anisotropic PS/poly(methyl methacrylate) (PMMA) core formed, and then snowman-shaped Janus particles were achieved because the swollen core ruptured the shell to form a hole and extruded from it. It is a general method to adjust the anisotropic structural modulation of Janus particles, resulting in pistachio or snowman shapes. In this general way, thermo-stimulated pistachio-shaped Janus particles were also fabricated and were used as temperature-responsive solid surfactants to adaptively adjust the as-stabilized Pickering emulsion.