Although the concept of Janus particles was raised in the early 1990s, the related research has not attracted considerable interest until recently due to the special properties and applications of these colloidal particles as well as the advances in new fabrications. Janus particles can be divided into three categories: polymeric, inorganic, and polymeric-inorganic, and each kind of Janus particles can be spherical, dumbbell-like, half raspberry-like, cylindrical, disk-like, or any of a variety of other shapes. Different Janus particles may share common preparation principles or require specific fabrication processes, and may have different assembly behaviours and properties. This critical review discusses the main fabrication methods of the three kinds of Janus particles, and then highlights the important properties and applications of these Janus particles developed in recent years, and finally proposes some perspectives on the future of Janus particle research and development.

The fabrication of monodisperse hollow spheres with controllable size and shape is currently one of the fastest growing areas of materials research since the pioneering works of Kowalski et al. and Blankenship at Rohm and Haas. [1,2] The resulting hollow nano-and microspheres are of great technological importance for their potential applications in catalysis, chromatography, protection of biologically active agents, fillers (or pigments/coatings), waste removal, and large bimolecular-release systems. [3][4][5][6][7][8][9][10][11][12][13] As shown in recent studies, a variety of chemical and physicochemical methods, including heterophase polymerization combined with a sol-gel process, [14,15] emulsion/interfacial polymerization strategies, [16][17][18] spray-drying methods, [19,20] self-assembly techniques, [21][22][23] and surface living polymerization processes, [24][25][26] have been employed to prepare hollow spheres that consist of polymeric or ceramic materials. Two of them are particularly interesting and are usually used to fabricate hollow spheres with homogeneous, dense layers. One is templating against colloidal particles (including gold, [27] CdS, [28] Pb, [7] and mesoscale ZnS, [29] or polymer beads [30,31] ). In a typical procedure, template particles are coated in solution either by controlled surface precipitation of inorganic molecule precursors (silica, titania, etc.) or by direct surface reactions that utilize specific functional groups on the cores to create core/shell composites. The template particles are subsequently removed by selective dissolution in an appropriate solvent or by calcination at elevated temperatures in air to generate ceramic hollow spheres. For instance, Bourgeat-Lami and co-workers [15] have synthesized polystyrene (PS) latex particles bearing silanol groups on the surface via emulsion polymerization using 3-(trimethoxysilyl)propyl methacrylate as a functional comonomer; these PS colloids are then transferred into aqueous ethanol solution by exchange of solvent, wherein the co-condensation of the silanol groups with tetraethoxysilane (TEOS) is carried out via an ammonia-catalyzed sol-gel process, which gives rise to composite particles with PS as a core and silica as the shell. Hollow silica spheres are obtained in a following step by thermal degradation of the PS cores at 600°C. Another method, termed the layer-by-layer (LbL) self-assembly technique, is becoming a very attractive topic of investigation since the pioneering work done by Caruso et al. [3,9] The basis of this process is the electrostatic association between alternately deposited, oppositely charged species. Multilayered shells are assembled onto submicrometer-sized colloidal particles by the sequential adsorption of polyelectrolytes and oppositely charged nanoparticles. Upon calcination of the obtained core/shell particles, uniform-sized hollow spheres of various diameters and wall thickness can be generated for a variety of inorganic materials, including silica, iron oxide, titania, zeolite, clay, and ino...

Superhydrophobic coatings that are also self‐healing have drawn much attention in recent years for improved durability in practical applications. Typically, the release of the self‐healing agents is triggered by temperature and moisture change. In this study, UV‐responsive microcapsules are successfully synthesized by Pickering emulsion polymerization using titania (TiO2) and silica (SiO2) nanoparticles as the Pickering agents to fabricate all‐water‐based self‐repairing, superhydrophobic coatings. These coatings are environmentally friendly and can be readily coated on various substrates. Compared to conventional superhydrophobic coatings, these coatings can regenerate superhydrophobicity and self‐cleaning ability under UV light, mimicking the outdoor environment, after they are mechanically damaged or contaminated with organics. They can maintain the superhydrophobicity after multiple cycles of accelerated weathering tests.

Marine biofouling has been plaguing people for thousands of years. While various strategies have been developed for antifouling (including superoleophobic) coatings, none of these exhibits self-healing properties because the bestowal of a zoetic self-repairing function to lifeless artificial water/solid interfacial materials is usually confronted with tremendous challenges. Here, we present a self-repairing underwater superoleophobic and antibiofouling coating through the self-assembly of hydrophilic polymeric chain modified hierarchical microgel spheres. The obtained surface material not only has excellent underwater superoleophobicity but also has very good subaqueous antibiofouling properties. More importantly, this surface material can recover the oil- and biofouling-resistant properties once its surface is mechanically damaged, similar to the skins of some marine organisms such as sharks or whales. This approach is feasible and easily mass-produced and could open a pathway and possibility for the fabrication of other self-healing functional water/solid interfacial materials.

The SiO(2)/polystyrene nanocomposite particles were synthesized through miniemulsion polymerization by using sodium lauryl sulfate surfactant (SLS), hexadecane costabilizer in the presence of silica particles coated with methacryloxy(propyl)trimethoxysilane. Core-shell or other interesting morphology composite particles were obtained depending on the size of the silica particles and the surfactant concentration employed. By adjusting these parameters, it was possible to control the size and morphology of the composite particles.