A reversible transformation of overall shape and internal structure as well as surface composition of nanostructured block copolymer particles is demonstrated by solvent-adsorption annealing. Polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) pupa-like particles with PS and P4VP lamellar domains alternatively stacked can be obtained by self-assembly of the block copolymer under 3D soft confinement. Chloroform, a good solvent for both blocks, is selected to swell and anneal the pupa-like particles suspended in aqueous media. Reversible transformation between pupa-like and onion-like structures of the particles can be readily tuned by simply adjusting the particle/aqueous solution interfacial property. Interestingly, poly(vinyl alcohol) (PVA) concentration in the aqueous media plays a critical role in determining the particle morphology. High level of PVA concentration is favorable for pupa-like morphology, while extremely low concentration of PVA is favorable for the formation of onion-like particles. Moreover, the stimuli-response behavior of the particles can be highly suppressed through selective growth of Au nanoparticles within the P4VP domains. This strategy provides a new concept for the reversible transformation of nanostructured polymer particles, which will find potential applications in the field of sensing, detection, optical devices, drug delivery, and smart materials fabrication.

Another face to Janus particles: Silica Janus nanosheets were synthesized by crushing Janus hollow spheres formed by self‐assembled materialization of an amphiphilic emulsion interface. The Janus nanosheets serve as solid surfactants and can be used collecting oil or hazardous chemical spills.

Janus nanodiscs of diblock copolymers are prepared by stepwise disassembly of PS-b-P4VP disc-stacked particles. The Janus nanodiscs are uniform in thickness and regular in contour. By preferential growth of functional materials at the positively charged P4VP side, the composition, microstructure, and performance of the Janus nanodiscs are tunable.

Janus composites with two different components divided on the same object have gained growing interest in many fields, such as solid emulsion stabilizers, sensors, optical probes and self-propellers. Over the past twenty years, various synthesis methods have been developed including Pickering emulsion interfacial modification, block copolymer self-assembly, microfluidics, electro co-jetting, and swelling emulsion polymerization. Anisotropic shape and asymmetric spatial distribution of compositions and functionalities determine their unique performances. Rational design and large scale synthesis of functional Janus materials are crucial for the systematical characterization of performance and exploitation of practical applications.

Janus hollow silica spheres with an asymmetric shell are synthesized by self-assembled sol-gel process at an emulsion interface, and desired materials can be preferentially laden inside the cavities from their surroundings.

Nano-objects are generated through 3D confined supramolecular assembly, followed by a sequential disintegration by rupturing the hydrogen bonding. The shape of the nano-objects is tunable, ranging from nano-disc, nano-cup, to nano-toroid. The nano-objects are pH-responsive. Functional materials for example inorganic or metal nanoparticles are easily complexed onto the external surface, to extend both composition and microstructure of the nano-objects.

Janus colloidal particles with hierarchical structures are generated by phase separation of diblock copolymer polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) and homopolymer poly(methyl methacrylate) (PMMA) binary blends in confined geometry. The dependence of their morphology on the copolymer composition, solvent selectivity, particle size, and polymer/aqueous solution interfacial property was investigated. By varying the particle/ aqueous solution interfacial property alternately, the Janus particles exhibited a reversible morphological transformation under solvent-adsorption annealing process. In addition, by introducing 3-n-pentadecyphenol (PDP) which can hydrogen bond with P4VP to form supramolecules, the structure of the Janus particles can be well tuned. Furthermore, due to the complexation of pyridine unit with Au precursor, composite Janus particles with Au nanoparticles selectively incorporated in P4VP microdomains can be easily manipulated.

We present with experiments and computer simulations that colloidal molecules with tunable geometry can be generated through 3D confined assembly of diblock copolymers. This unique self-assembly can be attributed to the slight solvent selectivity, nearly neutral confined interface, deformable soft confinement space, and strong confinement degree. We show that the symmetric geometry of the colloidal molecules originates from the free energy minimization. Moreover, these colloidal molecules with soft nature and directional interaction can further self-assemble into hierarchical superstructures without any modification. We anticipate that these new findings are helpful to extend the scope of our knowledge for the diblock copolymer self-assembly, and the colloidal molecules with new composition and performance will bring new opportunities to this emerging field.