In recent years, much attention has been devoted to the synthesis of anisotropic nanoparticles, and in particular of Janus Nanoparticles. In this work, a two-step emulsion based polymerization has been applied to synthesize Janus dumbbell nanoparticles, which size and morphology can be tuned by changing the process parameters. Narrowly distributed polystyrene nanoparticles are used as seeds, covering a wide range of sizes. These seeds are fist coated with a random copolymer of styrene and 3-trimethyloxyxilyl propyl acrylate (MPS), bringing silane groups on the surface of the seeds. The particles are then swollen with a monomer solution before a second polymerization. Due to the hydrophilic shell on the surface of the nanoparticles, the newly formed polymer is bulging out of the seeds, giving birth to dumbbell-like nanoparticles. Depending on the amount of swelling, dumbbells with different aspect ratio can be prepared. The resulting nanoparticles are not only anisotropic in shape, but also in surface chemistry. Only the first bulb is bearing silane groups, which can be functionalized by means of silane chemistry. Positively changed groups have been added to the surface of the nanoparticles, so as to create dipolar particles. Several types of negatively charged nanocrystals can be attached to the positively charged bulb of the dumbbells. Superparamagnetic iron oxide nanoparticles (SPIONS) allow the preparation of magnetic hybrid particles, which align into peculiar chain-structures depending on their size and aspect-ratio. The same approach has been used for platinum nanocrystals, leading to particles that can be used as Janus nanomotors in H2O2 solution. Additionally, silica shell can be grown on top of the silane functionalized bulb, followed by polymer removal, finally leading to silica nanobowls.
marco.lattuada@unifr.ch
