Janus nanoparticles synthesis

Fig. 20 Synthesis of Janus nanoparticles using a combination of polymer single-crystal templating with SI-ATRP. Reprinted with permission from Zhou et al. [205]...

Janus micelles are non-centrosymmetric, surface-compartmentalized nanoparticles, in which a cross-linked core is surrounded by two different corona hemispheres. Their intrinsic amphiphilicity leads to the collapse of one hemisphere in a selective solvent, followed by self-assembly into higher ordered superstructures. Recently, the synthesis of such structures was achieved by crosslinking of the center block of ABC triblock copolymers in the bulk state, using a morphology where the B block forms spheres between lamellae of the A and C blocks [95, 96]. In solution, Janus micelles with polystyrene (PS) and poly(methyl methacrylate) (PMMA) half-coronas around a crosslinked polybutadiene (PB) core aggregate to larger entities with a sharp size distribution, which can be considered as supermicelles (Fig. 20). They coexist with single Janus micelles (unimers) both in THF solution and on silicon and water surfaces [95, 97]. 

Perro A et al (2005) Design and synthesis of Janus micro- and nanoparticles. J Mater Chem 15(35-36) 3745-3760... 

Muller and coworkers prepared disc-like polymer Janus particles from assembled films of the triblock copolymer SBM and, after hydrolysis of the ester groups into methacrylic acid units, used these as Pickering stabilizer in the soap-free emulsion polymerization of styrene and butyl acrylate [111]. Armes and coworkers described the synthesis of PMMA/siUca nanocomposite particles in aqueous alcoholic media using silica nanoparticles as stabilizer [112], extending this method to operate in water with a glycerol-modified silica sol [113, 114]. Sacanna showed that methacryloxypropyltrimethoxysilane [115] in the presence of nanosized silica led to spontaneous emulsification in water, which upon a two-step polymerization procedure afforded armored particles with an outer shell of PMMA [116]. Bon and coworkers demonstrated the preparation of armored hybrid polymer latex particles via emulsion polymerization of methyl methacrylate and ethyl methacrylate stabilized by unmodified silica nanoparticles (Ludox TM O) [117]. Performance of an additional conventional seeded emulsion polymerization step provided a straightforward route to more complex multilayered nanocomposite polymer colloids (see Fig. 14). 

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